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Heartbeat perception and panic disorder: possible explanations for discrepant findings
Behat'. Res. Ther. Vol. 33, No. I, pp. 69-76, 1995
Pergamon
0005-7967(94)E0002-Z
Copyright © 1994 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0005-7967/95 $7.00 + 0.00
Heartbeat perception and panic disorder: possible explanations for discrepant findings ANKE EHLERSL3, PETER BREUER2, DIRK DOHN 3 a n d WOLFGANG FIEGENBAUM3
IDepartment of Psychiatry, University of Oxford, U.K. 'Department of Psychology, University of Gdttingen, and 3Christoph Dornier Foundation of Clinical Psychology, Marburg, German)' (Received 30 September 1993; received for publication 7 January 1994) Summary--Results on cardiac awareness in panic disorder are inconsistent. The present study attempted to clarify whether differences in instructions or the inclusion of patients taking antidepressant medication could account for these inconsistencies. 112 patients with panic disorder with agoraphobia were compared to 40 normal controls on the heartbeat perception task developed by Schandry (1981) [Schandry, R., Psychophysiology, 18, 483-488] using a standard instruction ("count all heartbeats you feel in your body") and a strict instruction ("count only those heartbeats about which you are sure"). Superior heartbeat perception for patients was only found with the standard instruction. Similarly, only with the standard instruction, patients taking medication affecting the cardiovascular system performed worse than patients without medication, as expected based on the relationship between stroke volume and heartbeat perception. The pattern of group differences indicates that agoraphobic patients have a better feeling for how fast their heart is beating than controls although these differences may be due to a tendency to interpret weak sensations as heartbeats. Furthermore, we tested in a subgroup of 40 patients whether cardiac awareness changes with exposure treatment. No changes in heartbeat perception were observed.
INTRODUCTION Palpitations are among the most common symptoms of panic attacks (Barlow, 1988; Margraf, Taylor, Ehlers, Roth & Agras, 1987). This has led researchers to raise the question of whether patients with panic disorder are better at perceiving their heartbeats than other people (see Ehlers, 1993, for a review). As Ehlers, Margraf and Roth (1988a) have hypothesized, such an increased cardiac awareness would be neither a necessary nor sufficient cause for panic attacks but--for those patients with good heartbeat perception--this factor could be involved in the development or maintenance of the disorder by increasing the probability of cardiac sensations which may trigger panic attacks if interpreted as threatening or by motivating the patient to avoid situations in which these sensations occur. Empirical studies on heartbeat perception in panic disorder have given inconsistent results. While some studies found greater cardiac awareness in patients with panic disorder (Ehlers & Breuer, 1992; Harbauer-Raum, 1987), the majority have yielded negative findings (e.g. Ehlers, Margraf, Roth, Taylor & Birbaumer, 1988b; Hartl, 1992). The purpose of the present paper is, first, to investigate whether methodological differences could have contributed to these inconsistencies, and second, to investigate whether cardiac awareness changes with treatment. Several studies have required the Ss to compare an external signal (series of tones) with the rhythm of their heartbeats. All these studies failed to find differences between panic disorder patients and controls no matter whether Ss had to adjust the rate of the stream of tones to their heart rate (Ehlers et al., 1988b) or had to distinguish between accurate and false feedback according to the discrimination paradigms of Katkin (Katkin, 1985; Ehlers, 1988) or Whitehead (Whitehead, Drescher, Heiman & Blackwell, 1977; Asmundson, Sandler, Wilson & Norton, 1993). One possible explanation for the lack of group differences with these paradigms is that the external signal may have distracted Ss from their internal cues (Pennebaker, 1982). Fur:hermore, the comparison of an external and internal signal may be much more difficult than the perception of an internal signal. This is in line with the fact that untrained Ss perform at chance levels in discrimination paradigms of heartbeat perception (Katkin, 1985). In the study of Asmundson et al. (1993), only male nonpanickers performed better than chance. Ehlers and Breuer (1992) have argued that the major question of interest to the study of panic disorder is how well patients can perceive whether their heart is beating fast or slow and whether they can detect arrhythmias, as these events may trigger panic attacks or motivate patients to avoid situations in which these sensations occur. This question cannot be answered with discrimination paradigms because these paradigms involve feedback on the rhythm of heartbeats. Increased accuracy in heartbeat perception in cardiac neurotics (Harbauer-Raum, 1987) and patients with panic disorder (Ehlers & Breuer, 1992) compared to normal controls was found with the mental-tracking paradigm developed by Schandry (1981). Subjects are required to count their heartbeats silently during signaled intervals without taking their pulse. This paradigm has a high face validity for the clinically important question of whether panic disorder patients have a good feeling for how fast their heart is beating. However, this paradigm has been criticized on the grounds that Ss may give spuriously correct answers without feeling their heartbeats if they estimate the time interval correctly and calculate the number of heartbeats from general knowledge of their heart rate (Montgomery & Jones, 1984). According to results of *To whom all correspondence should be addressed at: Department of Psychiatry, University of Oxford, Warneford Hospital, Oxford OX3 7JX, U.K. 69
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CASEHISTORIESAND SHORTERCOMMUNICATIONS
Ehlers and Breuer (1992, study 2), this interpretation is unlikely, because Ss performed much worse in a time estimation task than in the heartbeat perception task. Time intervals were usually overestimated, whereas the number of heartbeats was underestimated by the vast majority of Ss. Underestimation is to be expected if Ss are actually counting their heartbeats but miss a few beats because of inaccurate perception. Whereas Knoll, Folten and Hodapp (1991) reported a small marginally significant correlation between time estimation and performance in the mental-tracking task in non-anxious women (r = 0.20, P < 0.06), Ehlers and Breuer (1992) did not find such correlation. Antony, Meadows, Brown and Barlow (1993b) found a negative correlation (r = -0.48, P = 0.07). Overall, these results suggest that Ss do not simply estimate time intervals during the mental-tracking task. Two recent studies, however, did not replicate the superior performance of panic disorder patients in the mental-tracking paradigm (Antony, Brown, Craske, Barlow, Mitchell & Meadows, 1993a; Hartl, 1992). Several details of methodology may have contributed to these discrepant findings. One possibility concerns sample differences. First, differences in sample size may have resulted in different statistical power. Means in the Antony et al. (1993a, b) study pointed in the same direction as in the Ehlers and Breuer (1992) studies, but the group differences were not significant. However, the means in the Hartl (1992) study pointed in the opposite direction. One possible explanation for this result is that Hartl's controls had a lower body mass index than the patients and that slightly (nonsignificantly) more men were included in the control sample (45%) than in the patient sample (38%). Previous research has shown that female sex and obesity are associated with poorer heartbeat perception (see Ehlers & Breuer, 1992, for a summary). In the Ehlers and Breuer (1992) and Antony et al. (1993a) studies, patient and control groups were matched for sex, body mass index, and physical activity. In addition, the studies differed in the proportion of agoraphobic Ss included. Ehlers and Breuer (1992) found that patients with agoraphobia show a better heartbeat perception than patients with no avoidance. The Ehlers and Breuer sample included only 13.8% of patients without agoraphobic avoidance, compared to 24% in the Hartl (1992) sample. The Antony et al. (1993a, b) sample did not include any Ss with severe agoraphobia compared to 13.8% in the Ehlers and Breuer (1992) sample. It is possible that increased cardiac awareness is restricted to those patients with agoraphobic avoidance. Another difference between the studies that is of interest to the present paper is the inclusion of Ss taking medication. While Ehlers and Breuer (1992) excluded all S s who took medication affecting the cardiovascular system including tricyclic antidepressants, the panic disorder sample of Antony et al. (1993a, b) included 10% Ss on antidepressants. Hartl (1992) instructed patients not to take any medication on the test day. However, 24% had been regularly taking antidepressants on previous days. The inclusion of Ss on antidepressants is problematic because these drugs increase mean heart rates by about 15 bpm (Roth, Margraf, Ehlers, Haddad, Maddock, Davies, Agras & Taylor, 1992). Subjects with higher heart rates show a larger error in Schandry's heartbeat perception paradigm. Ehlers and Breuer found a correlation of r = 0.23 (P < 0.001) and Antony et al. (1993a, b) a correlation of r = 0.39 (P < 0.01) between heart rate and error scores. This relationship is probably mediated by the fact that accuracy in heartbeat perception depends on cardiac output. Schandry, Bestler and Montoya (1993) found a correlation of r = 0.59 between stroke volume and performance in the heartbeat perception task. Although not explicitly mentioned by Hartl (I 992), her instructions differed from those used by Ehlers and Breuer (1992; Hartl, personal communication, 1989). While Ehlers and Breuer told Ss to count the number of heartbeats they felt in their body, Hartl (1992) gave a stricter instruction and emphasized that the Ss should not make any guesses but should only count heartbeats they had really felt. This difference in instruction may have influenced the results in that it made Ss less likely to report a heartbeat in the Hartl study, resulting in much higher average error scores (for patients, sitting condition: approximately 58%, for controls approximately 44%--compared to 22 and 30% in the Ehlers and Breuer study, respectively). Hartl (1992) found that panic patients were more often unable to feel any heartbeat during a trial than controls. They were also less confident about their judgements than controls. However, the patient group showed a higher correlation between subjective confidence of perception and error in the heartbeat perception task (r = -0.76) than controls (r = -0.37) which would indicate a more realistic heartbeat perception in the patient group. It is possible that Hartl's patients experienced more performance anxiety than controls because Ss were tested in a clinical setting as a part of several heartbeat monitoring procedures run by a physician (Dr Hartl). Tests of their heart have a high relevance to panic disorder patients. This might have negatively affected their performance in this study. Also, the strict instruction may have made them more worried about erroneously reporting a beat that did not occur which would result in underreporting of heartbeats. In contrast, the Ss in the Ehlers and Breuer study were not tested in a clinical setting and this--together with the less strict instructions--possibly affected their state anxiety levels. Compared to patients' mean trait anxiety levels of 43.8 on the STAI-scale, the state anxiety levels of 49.4 in Hartl's study are high. This compares to a mean trait anxiety level of 51.7 in the Ehlers and Breuer study and a mean state anxiety of 44.6. Hartl (1992) found a correlation between state anxiety and poor heartbeat perception in panic patients (r = 0.26, < 0.10) whereas Ehlers and Breuer (1992) did not find such a correlation. The present study was designed to investigate the possible contribution of these methodological differences to the discrepant results. First, we wanted to clarify the influence o f instructions on comparisons between panic disorder patients and controls on Schandry's heartbeat perception paradigm. We compared the performance of agoraphobic patients and controls when using the instructions previously used by Ehlers and Breuer (1992) and when using a very strict instruction asking the Ss not to count any heartbeats about which they were not absolutely sure. Furthermore, we explored whether patients taking medication affecting their cardiovascular system differ in their heartbeat perception from patients without medication. These differences might be expected based on the correlations between stroke volume and heartbeat perception. In addition, we were interested in whether heartbeat perception changes with treatment. If heightened cardiac awareness is primarily a function of heightened anxiety, as Antony et al. (1993b) have suggested, patients' performance in the heartbeat perception test should deteriorate with successful treatment. The same result would be expected if superior heartbeat perception in panic disorder patients is primarily due to increased attention to internal cues based on their interoceptive fears. On the other hand, exposure therapy may enhance cardiac awareness because exposure induces cardiac sensations such as palpitations and thus might train Ss in heartbeat perception. Finally, heartbeat perception may be a relatively stable individual characteristic which is not influenced by treatment. Ehlers and Breuer (1992) did not find any differences in heartbeat perception between patients with current panic attacks and those in remission.
CASE HISTORIES AND SHORTER COMMUNICATIONS
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METHOD
Subjects Comparison of patients and controls. Patients with the DSM-III-R diagnosis of panic disorder with agoraphobia (N = 112) were recruited through the outpatient clinic o f the Christoph Dornier Foundation o f Clinical Psychology, Marburg, Germany. The clinic specializes on exposure therapy for anxiety disorders. Patients were interviewed by trained psychologists using the German version of the Anxiety Disorders Interview Schedule-Revised (ADIS, DiNardo & Barlow, 1988; German version: Diagnostisches Interview bei psychischen Sttrungen, DIPS, Margraf, Schneider, Ehlers, DiNardo & Barlow, 1991). Patients on medication affecting the cardiovascular system (e.g. tricyclic antidepressants, beta-blockers, or hypertensive medication) were excluded. Controls (N = 40) were recruited through advertisements in local newspapers and received 10 German Marks for their participation. They were matched to the patient group for sex and were to be comparable in age and body mass index, and had never experienced panic attacks or suffered from any psychiatric disorder according to the DIPS. Table I gives a description of the groups in terms of sex, age, body mass index, trait anxiety, as measured by the State-Trait-Anxiety Inventory (STAI-trait and STAI-state, Spielberger, Gorsuch & Lushene, 1970; German version, Laux, Glanzmann, Schaffner & Spielberger, 1981); depression, as measured by the Beck Depression Inventory (BDI, German version: Beck, Rush, Shaw & Emery, 1981); and degree of agoraphobic avoidance behavior, as measured by the Mobility Inventory (MI) scales Alone for avoidance when alone and Accompanied for avoidance when accompanied by a trusted companion (Chambless, Caputo, Jasin, Gracely & Williams, 1985; German version: Ehlers, Margraf & Chambless, 1993). Patients and controls did not differ in their sex, age, or body mass index. Patients had significantly higher trait and state anxiety, depression, and agoraphobic avoidance than controls. Comparison of patients with and without medication. Twenty-four additional patients (17 women, 7 men) were tested. They met DSM-III-R criteria for panic disorder with agoraphobia according to the DIPS. These patients had to be excluded from the patient group described above because they were taking medication affecting the cardiovascular system. To explore the possible effects of medication on performance in the heartbeat perception test, 107 patients (77 women, 30 men) who were not taking medication affecting the cardiovascular system were matched to the 24 patients on medication based on their sex and body mass index. Patients with and without medication did not differ in terms of age [t (129) = 1.16, P > 0.25], sex [12(l) = 0.01, P > 0.91], body mass index [t(129) = 0.27, P > 0.78], trait anxiety [t(104) = 0.24, P > 0.81], state anxiety [t(106) = 0.48, P > 0.63], depression [t(112) = 0.36, P > 0.72] or avoidance [MI-alone: t(112) = 0.44, P > 0.65; MI-accompanied: t(112) = 0.54, P > 0.58]. Patients before and after therapy. Forty of the agoraphobic patients (27 women, 13 men) who were not taking medication affecting the cardiovascular system were tested again after the end of treatment. This sample had a mean age of 36.1 years (SD = 9.5) and a mean body mass index of 23.0 (SD = 2.9). The treatment involved massed therapist-assisted and self-guided exposure to feared situations. Details of the treatment program are found in Fiegenbaum (1988). Mean duration of treatment was 32 h (SD: 7.5 h), including initial interviews and assessment. As shown in Table 2, treatment led to significant reductions in agoraphobic avoidance, anxiety and depression. Number of panic attacks also decreased during therapy. Note that the number of panic attacks at the end of treatment includes those occurring during the last month of treatment.
Heartbeat perception paradigm Heartbeat perception was assessed with the mental-tracking paradigm developed by Schandry (1981). Subjects were instructed to silently count their heart beats during signaled intervals of 35, 25 and 45 sec without taking their pulse or using any other strategies such as holding their breath. During each of the trials, Ss were first presented with a warning stimulus (800 Hz, 65 dB, 100 msec) preparing them for the trial. The warning stimulus was given 500 msec after a R-wave of the S's electrocardiogram. The start signal (1000 Hz, 65 dB, 50 msec) was triggered immediately after the third R-wave following the warning stimulus. The tone signaling the end of the counting period (1000 Hz, 65 dB, 50 msec) was given when the interval of 35, 25, or 45 sec was up and 300 msec after the last R-wave had elapsed. The computer program determined the number of R-waves occurring during the counting interval. Three blocks of three trials o f the mental tracking paradigm were run. For the first two blocks, Ss received the standard instruction used by Ehlers and Breuer (1992) to count all the heartbeats they felt in their body. During one of the blocks, a distracting series of tones was given while Ss were counting their heartbeats. The tones had a volume of 70 dB and frequencies between 80 and 170 Hz. Frequencies were randomly given with the restriction of a minimum difference of 10 Hz between consecutive tones. The inter-tone-interval was 600 msec. This block was run to investigate the possible effects of distracting external signals on Ss' performance in the mental tracking paradigm. The two trials with the standard instruction with and without distracting tones were presented in balanced order. In the third block, Ss were given the very strict instruction to only count the heartbeats that they had really felt in their body.They were asked to refrain from counting any heartbeats about which they were not sure and which would represent an estimated heartbeat rather than one really felt. After each trial, Ss were asked to rate the confidence with which they had felt their heartbeats on a scale between 0 "totally uncertain" to 10 "totally certain". Table 1. Patient and control samples
Age (years) Sex Women Men Body Mass Index STAI-trait -state BDI MI-alone -accompanied
Patients (N = 112)
Controls (N = 40)
36.3 (7.7) N = 76 (67.9%) N = 36 (32.1%) 23.7 (3.0) 53.9 (9.9) 51.9 (12.4) 16.6 (8.5) 3.23 (I.01) 2.26 (0.87)
36.4 (9.1) N = 27 (67.5%) N = 13 (32.5%) 22.6 (3.8) 32.8 (7.1) 31.7 ( 7 . 8 ) 2.7 ( 2 . 9 ) 1.17 (0.24) 1.06 (0.15)
T-test or ;(2-test t(150) = 0.12, NS ~2(1) = 0.002, NS t(55.51) = t(87.05) = t(107.15)= t(130.13)= t(117.93)~ t(108.59)=
If not indicated otherwise, the table shows means (standard deviations). BRT 331--F
1.63, NS 13.28, P < 0.001 11.14, P < 0.001 14.09, P < 0.001 18.68, P < 0.001 13.02, P < 0.001
72
CASE HISTORIESAND SHORTERCOMMUNICATIONS Table 2. Questionnaire scores of 40 patients before and after treatment
STAl-trait -state BDI Ml-alone -accompanied Panic attacks/ month
Before treatment
After treatment
52.4 (9.6) 50.4 (10.0) 15.0 (8.4) 3.25 (1.14) 2.33 (0.97)
44.3 (9.4) 40.0 (9.5) 7.1 (5.9) 1.63 (0.61) 1.27 (0.28)
I 1.1 (18.2)
4.0 (8.0)
t -Test t(21) t(21) t(23) t(35) t(35)
= ~ = = =
4.59, 4.55, 6.26, 9.83, 6.83,
P P P P P
< < < < <
0.001 0.001 0.001 0.001 0.001
t(28) = 2.06, P < 0.05
Protocol Patients o f the Christoph Dornier Foundation of Clinical Psychology were diagnosed with the DIPS (Margraf et aL, 1991). During the baseline assessment before treatment they answered questionnaires, received a medical cheek-up and participated in the heartbeat perception test. For the test day, S s were instructed to abstain from alcohol, to eat just a light meal, not to smoke more than usual and not to drink more caffeine-containing beverages than usual. After electrodes had been attached, S s were asked to take off their watches for the duration of the test. For each of the blocks of the heartbeat perception paradigm, S s received written instructions. The experimenter answered possible questions, and then demonstrated the different signals. A short test trial of 12 see was run to check whether Ss had understood the task. Each block consisted of three trials of the mental tracking paradigm lasting 35, 25, and 45 see. During the tasks, Ss sat alone in a comfortable arm chair. They could not see the experimenter, but could communicate with her or him via intercom. T h r o u g h a one-way mirror, the experimenter checked whether Ss complied with the instruction not to take their pulse during the heartbeat perception task. A subgroup of 40 patients was tested again with the same protocol after the end of exposure treatment. Assessment Degree of inaccuracy in heart beat perception was defined as the modulus o f actual number of heart beats minus counted heart beats, divided by actual heart beats and multiplied by I00 to express as a percentage i.e. lAB -
-
CBI
-
x
AB
100
where AB = actual beats and CB = counted beats. Mean error scores were obtained from the average of the three trials for each of the three blocks. Schandry (1985) argued that percent error scores are superior to simple difference scores as Ss with higher heart rates have a greater chance of missing heart beats during the counting interval. For example, if Ss A and B both feel every second heart beat, and subject A has a heart rate of 50 while subject B has a heart rate o f I00, the difference between the n u m b e r of counted beats and the number of real heart beats is 100% higher in S B than in S A whereas their performance is regarded equivalent according to Schandry's analysis. All significance levels are two-tailed. RESULTS
Comparison o f patients and controls The results of the three blocks of the heartbeat perception test are found in Table 3. Table 3 also shows the Ss' mean heart rates for each of the blocks. Based on the results of the previous studies of Ehlers and Breuer (1992) and Hartl (1992), the following hypotheses for the mean error in heartbeat perception were evaluated by planned comparisons. Table 3. Heart rates and heartbeat perception of patients and controls means (standard deviations)
Heart rate (bpm) Experimental condition Standard instruction Standard instuction with distraction Strict instruction
Patients (N = 112)
Controls (N = 40)
t-Test
79.8 (13.7)
71.3 (11.5)
t(150) ffi 3.54, P < 0.001
73.2 (12.8) 77.7 (11.8)
65.1 (9.9) 70.5 (9.9)
t(150) = 3.64, P < 0.001 t(150) = 3.45, P < 0.001
Error in heartbeat perception (% heart rate) Experimental Patients Controls condition (N = 112) (N = 40) Standard instruction 27.6 (21.6) 35.1 (25.0) Standard instruction with distraction 30.1 (20.4) 38.9 (29.5) Strict instruction 62.0 (32.6) 67.6 (30.7) Confidence rating (0-10) Experimental Patients Controls condition (N = 94) (N = 37) Standard instruction Standard instruction with distraction Strict instruction NS = nonsignificant.
ANCOVA F(I,149) = 4.43, P < 0.05 F(I,149) = 5.73, P < 0.05 F(I, 149) = 1.07, NS
t-Test
5.62 (2.32)
5.89 (2.49)
t(129) =0.59, NS
4.61 (2.34) 5.92 (2.49)
6.00 (2.44) 7.05 (2.44)
t(129) = 3.04, P < 0.01 t(129) = 2.35, P < 0.05
CASE HISTORIESAND SHORTERCOMMUNICATIONS
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Table 4. Percentage of subjects who could not feel any heartbeat Experimental condition
Trial
Standard instruction
Patients Controls (N = 112) (N = 40)
I 2 3 1 2 3 I 2 3
Standard instruction with distraction Strict instruction
0.9 2.7 1.8 0.9 0.9 1.8 22.3 16.1 18.0
10.0 7.5 10.0 7.5 10.0 12.5 30.0 22.5 25.0
Fisher's exact/~2tests P < 0.05 NS P < 0.05 P < 0.06 P < 0.05 P < 0.05 NS NS NS
NS = nonsignificant.
• Patients show a higher accuracy of heartbeat perception (lower error score) than controls if the standard instruction is used (Ehlers & Breuer, 1992). • No group differences are found if a very strict instruction is used (Hartl, 1992). Since the patient group showed significantly higher heart rates and since heart rate and error in heartbeat perception are positively correlated, we used ANCOVAs with heart rate as the covariate to evaluate group differences. The results are in line with the hypotheses. Patients showed a lower error score in the mental tracking paradigm only with the standard instruction, not with the very strict instruction. The two standard instruction blocks with and without distraction both showed differences between the groups. Hartl's (1992) observation that panic disorder patients may be less certain about their heartbeats was evaluated first by comparing the mean confidence ratings for each of the blocks (t-tests) and by calculating the number of Ss for each trial who could not feel any heartbeats (Table 4). For the standard instruction block without distraction (equivalent to the protocol of Ehlers & Breuer, 1992) patients and controls did not differ in their confidence of heartbeat perception. In the other two blocks (standard instruction with distraction, strict instruction) patients were less certain about their heartbeats as also reported by Hartl (1992). Patients with better heartbeat perception gave higher confidence ratings for standard instruction conditions (without distraction: r = -0.21, P < 0.05; with distraction: r = -0.25, P < 0.05). For controls, these correlations were in the opposite direction (without distraction: r =0.15, NS; with distraction: r =0.30, P <0.10). Differences in correlation between patients and controls tended to be significant (without distraction: P <0.10; with distraction: P < 0.001). No correlation between performance and confidence was found for the strict instruction condition in either group. Hartl's observation that panic disorder patients are more likely than controls not to feel any heartbeat at all was not replicated. On the contrary, for the standard instruction trials more controls than patients tended to be unable to feel their heartbeats.
Comparison o f patients with and without medication Table 5 presents the comparisons of patients who were and those who were not taking medication affecting the cardiovascular system. In the standard instruction block without distraction, patients on medication had higher error scores in heartbeat perception than those without medication. A similar trend was observed in the standard instruction block with distracting tones. The strict instruction condition did not yield group differences. No group differences were observed for confidence ratings or heart rates.
Table 5. Comparison of patients with and without medication means (standard deviations)
Heart rate (bpm) Experimental condition Standard instruction Standard instruction with distraction Strict instruction
Without medication (N = 107)
With medication (N = 24)
t-Test
80.4 (13.7)
82.9 (14.4)
t(129) = 0.81, NS
73.7 (13.0) 78.1 (11.9)
76.0 (12.6) 80.8 (13.8)
t(129) = 0.80, NS t(129) = 0.96, NS
Error in heartbeat perception (% heart rate) Experimental condition Standard instruction Standard instruction with distraction Strict instruction
Without medication (N = 107)
With medication (N = 24)
28.7 (21.7)
39.9 (29.8)
t(129) = 2.12, P <0.05
30.6 (20.4) 63.2 (33.0)
40.0 (28.8) 68.4 (30.9)
t(129) = 1.88, P < 0.07 t(129) = 0.71, NS
Without medication (N = 107)
With medication (N = 24)
t -Test
5.73 (2.47)
6.46 (2.09)
t(ll0) = 1.26, NS
4.63 (2.40) 6.06 (2.64)
5.59 (2.33) 6.35 (2.97)
t(ll0) = 1.65, NS t(110) = 0.44, NS
t-Test
Confidence rating (0-10) Experimental condition Standard instruction Standard instruction with distraction Strict instruction NS = nonsignificant.
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CASE HISTORIES A N D SHORTER COMMUNICATIONS
Table 6. Comparison of 40 patients before and after exposure treatment means (standard deviations) Heart rate (bpm) Experimental Before After condition treatment treatment t-Test Standard instruction Standard instruction with distraction Strict instruction
81.8 (14.7)
83.2 (16.9)
t(39) = -0.51, NS
75.6 (13.8) 80.4 (13.6)
76.3 (15.7) 82.7 (15.8)
t(39) = -0.25, NS t(39) = -0.80, NS
Error in heartbeat perception (% heart rate) Experimental Before condition treatment
After treatment
t-Test
Standard instruction Standard instruction with distraction Strict instruction
27.9 (21.1)
32.0 (22.0)
t(39) = -1.30, NS
29.1 (20.3) 62.4 (31.8)
30.2 (24.1) 63.6 (32.7)
t(39) = -0.35, NS t(39) = -0.25, NS
Confidence rating (0-10) Experimental condition
Before treatment
After treatment
5.32 (2.43)
5.47 (2.34)
t(26) = -0.32, NS
4.73 (2.08) 6.05 (2.28)
4.47 (2.36) 5.80 (2.49)
t(26) = 0.77, NS t(26) = 0.53, NS
Standard instruction Standard instruction with distraction Strict instruction
t-Test
NS = nonsignificant.
Patients before and after therapy
Table 6 gives the results o f the heartbeat perception tests before and after treatment. No changes in heartbeat perception, heart rate, or confidence ratings were observed. Correlations between the two tests were r = 0.58, r = 0.57, and r = 0.64 for the standard instruction conditions without and with distraction, and the strict instruction condition, respectively (all P's < 0.001).
DISCUSSION The study replicated the apparently contradictory pattern of group differences between panic patients and normal controls previously reported by Ehlers and Breuer (1992) and Hartl (1992): When the instruction "count the heartbeats you feel in your body" was used, panic disorder patients with agoraphobia showed a better heartbeat perception than controls and had the same level of confidence in their perceptions. When the instruction "count the heartbeats that you really feel and about which you are sure" was used, no group differences in accuracy were found, but patients were less certain about their perception than controls. This pattern of results indicates that agoraphobic patients have a better general feeling for how fast their heart is beating than controls. Group differences in correlations between performance in the mental-tracking task and confidence ratings found in Hartrs (1992) and the present study further indicate that patients tend to have more realistic perceptions of their accuracy than controls. On the other hand, confidence ratings showed that patients can be more easily made uncertain by distraction or strict instructions than controls. The latter could be related to the fact that patients are more worried about their heart and probably attach more significance to the test results than controls, This is especially the case if Ss are tested in a clinical setting like in Hartrs (1992) or the present study. The difference o f patients taking medication and those not taking medication in the standard instruction conditions underscores the validity of the group differences found with this paradigm. Patients taking medication affecting the cardiovascular system were less accurate in perceiving their heartbeats than those without medication. The strict instruction condition probably yields floor effects and is not sensitive enough to show group differences in cardiac perception. The effect of medication on heartbeat perception needs to be confirmed with different designs such as studying patients before and after they start taking medication. We cannot rule out that effects of self-selection contributed to the present finding. Patients with poor interoception may tolerate the side effects o f medication such as tricyclic antidepressants better than patients with good interoception. The present results also show limitations of the heartbeat tracking paradigm in assessing Ss' ability to perceive their heartbeats. Instructional sets had large effects on the number of heartbeats which Ss counted. However, it is highly unlikely that Ss in the standard instruction condition reported heartbeats without any corresponding sensation (false alarms). The vast majority o f Ss, patients as well as controls, reported fewer heartbeats than had actually occurred. This pattern is to be expected if Ss count their heartbeats but miss a few because of inaccurate perception. In the rare cases that Ss overestimated the number of heartbeats only very few additional heartbeats were reported. Further findings support the validity o f the standard instruction paradigm: The differences between patients taking medication affecting the cardiovascular system and those without medication, the high correlations between stroke volume and test results reported by Schandry et al. (1993), and the lack o f correlations between accuracy of time estimation and performance in the heartbeat perception task reported by Ehlers and Breuer (1992), and relationship of good heartbeat perception and maintenance of panic attacks in a prospective one year follow-up study (Ehlers, in press). Therefore it is highly unlikely that Ss just guess the number of heartbeats during the standard instruction paradigm. However, it is possible that panic disorder patients and controls differ in their tendency to think that a heartbeat has occurred when the corresponding sensation is rather weak. Both a tendency to interpret weak sensations as heartbeats as well as differences in ability to discriminate heartbeats would have the effect that panic patients tend to feel more of their heartbeats than controls. This could feed into the vicious cycle culminating in a panic attack (Clark, 1986; Ehlers et al., 1988a) or motivate the patient to
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75
avoid exciting, anxiety-provoking or strenuous activities and situations. This interpretation is supported by our finding that heartbeat perception measured with the standard instruction predicts relapse in panic patients in remission and maintenance of panic attacks in infrequent panickers and treated panic patients (Ehlers, in press). The lack of differences and relatively high correlations of heartbeat perception scores before and after treatment indicates that heartbeat perception is a relatively stable individual characteristic which is not influenced in a systematic way by exposure treatment. Similar results were recently reported by Antony et al. (1993b). This group compared 15 patients with panic disorder before and after cognitive-behavioral treatment. This lack of changes with treatment is in line with our previous finding that patients with current panic attacks do not differ from those in remission (Ehlers & Breuer, 1992). Therefore, it is unlikely that increased cardiac awareness is a function of heightened anxiety per se.
Acknowledgements--The research described in this paper was supported by a grant from the Deutsche Forschungsgemeinschaft (Eh 97/1-4). We would like to thank Kathrin Kluwe and Monika Freitag for their help. Anke Ehlers is supported by a Wellcome Principal Fellowship.
REFERENCES
American Psychiatric Association (1980). Diagnostic and Statistical Manual of Mental Disorders, Third Edition (DSM-III). Washington, D.C.: American Psychiatric Press. American Psychiatric Association (1987). Diagnostic and Statistical Manual of Mental Disorders, Third Edition-Revised (DSM-III-R). Washington, D.C.: American Psychiatric Press. Antony, M. M., Brown, T. A., Craske, M. G., Barlow, D. H., Mitchell, W. B. & Meadows, E. A. (1993a). Accuracy of heart beat perception in panic disorder, social phobia, and non-anxious subjects. Submitted. Antony, M. M., Meadows, E. A., Brown, T. A. & Barlow, D. H. (1993b). Cardiac awareness before and after cognitive-behavioral treatment for panic disorder. Submitted. Asmundson, G. J. G., Sandier, L. S., Wilson, K. G. & Norton, G. R. (1993). Panic attacks and interoceptive acuity for cardiac sensations. Behaviour Research and Therapy, 31, 193-197. Barlow, D. H. (1988). Anxiety and its disorders. New York: Guilford Press. Beck, A. T., Rush, A. J., Shaw, B. F. & Emery, G. (1981). Kognitive Therapie der Depression. Miinchen: Urban & Schwarzenberg. Brener, J. & Kluvitse, C. (1988). Heartbeat detection: Judgements of the simultaneity of external stimuli and heart beats. Psychophysiology, 25, 554-561. Chambless, D. L., Caputo, G. C., Jasin, S. E., Gracely, E. J. & Williams, C. (1985). The Mobility Inventory for agoraphobia. Behaviour Research and Therapy, 23, 35-44. Clark, D. M. (1986). A cognitive approach to panic. Behaviour Research and Therapy, 24, 461-470. DiNardo, P. A. & Barlow, D. H. (1988). Anxiety Disorders Schedule--Revised (ADIS-R). Albany, N.Y.: Graywind. Ehlers, A. (1988). Interozeption and selektive Aufmerksamkeit bei Personen mit Panikanfiillen. Unpublished research report, German Research Foundation. Ehlers, A. (1993). Interoception and panic disorder. Advances of Behaviour Research and Therapy, 15, 3-21. Ehlers, A. (in press). Factors associated with the maintenance of panic attacks: a one-year prospective study. Journal of Abnormal Psychology. Ehlers, A. & Breuer, P. (1992). Increased cardiac awareness in panic disorder. Journal of Abnormal Psychology, 101, 371-382. Ehlers, A., Margraf, J. & Chambless, D. L. (1993). Fragebogen zu k6rperbezogenen Angsten, Kognitionen und Vermeidung. Weinheim: Beltz. Ehlers, A., Margraf, J. & Roth, W. T. (1988a). Selective information processing, interoception, and panic attacks. In Hand, I. & Wittchen, H. U. (Eds), Panic and phobias 2 (pp. 129-148). Berlin: Springer. Ehlers, A., Margraf, J., Roth, W. T., Taylor, C. B. & Birbaumer, N. (1988b). Anxiety induced by false heart rate feedback in patients with panic disorder. Behaviour Research and Therapy, 26, l-I 1. Fiegenbaum, W. (1988). Long-term efficacy of ungraded versus graded massed exposure in agoraphobia. In Hand, I. & Wittchen, H. U. (Eds.), Panic and phobias 2 (pp. 83-88). Berlin: Springer. Harbauer-Raum, U. (1987). Wahrnehmung von Herzschlag und Herzarrhythmien--Eine Labor-Feldstudie an Patienten mit Herzphobie. In Nutzinger, D. O., Pfersmann, D., Welan, T. & Zapotoczky, H. G. (Eds), Herzphobie (pp. 84-91). Stuttgart: Enke. Hartl, L. A. (1992). Die Panikstb'rung. Eine Untersuchung zur Rolle der Wahrnehmung yon K6rperprozessen. Frankfurt: Peter Lang. Katkin, E. S. (1985). Blood, sweat, and tears: Individual differences in autonomic self-perception. Psychophysiology, 22, 125-137. Knoll, J. F., Folten, A. & Hodapp, V. (1991). Heart rate perception ability: A comparison of two methods. Journal of Psychophysiology, 5, 113. Laux, L., Glanzmann, P., Schaffner, P. & Spielberger, C. D. (1981). Das State-Trait Angstinventar. Weinheim: Beltz. Margraf, J., Schneider, S., Ehlers, A., DiNardo, P. & Barlow, D. H. (1991). Diagnostisches Interview bei psychischen Stdrungen (DIPS). Berlin: Springer. Margraf, J., Taylor, C. B., Ehlers, A., Roth, W. T. & Agras, W. S. (1987). Panic attacks in the natural environment. Journal of Nervous and Mental Disease, 175, 558-565. Montgomery, W. A. & Jones, G. E. (1984). Laterality, emotionality, and heartbeat perception. Psychophysiology, 21, 459-465. Pennebaker, J. W. (1982). The psychology of physical symptoms. New York: Springer. Roth, W. T., Margraf, J., Ehlers, A., Haddad, J. M., Maddock, R. J., Davies, S., Agras, W. S. & Taylor, C. B. (1992). Imipramine and alprazolam effects on stress reactivity in panic disorder. Biological Psychiatry, 27, 1231-1243. Schandry, R. (1981). Heart beat perception and emotional experience. Psychophysiology, 18, 483-488.
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Schandry, R., Bestler, M. & Montoya, P. (1993). On the relationship between cardiodynamics and heartbeat perception. Psychophysiology, 30, 467-475. Spielberger, C. D., Gorsuch, R. L. & Lushene, R. E. (1970). State-trait anxiety inventory. Palo Alto, CA: Consulting Psychologists Press. Whitehead, W. E., Drescher, V. M., Heiman, P. & Blackwell, B. (1977). Relation of heart rate control to heartbeat perception. Biofeedback and Self-Regulation, 2, 371-392.
Pergamon
0005-7967(94)E0002-Z
Copyright © 1994 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0005-7967/95 $7.00 + 0.00
Heartbeat perception and panic disorder: possible explanations for discrepant findings ANKE EHLERSL3, PETER BREUER2, DIRK DOHN 3 a n d WOLFGANG FIEGENBAUM3
IDepartment of Psychiatry, University of Oxford, U.K. 'Department of Psychology, University of Gdttingen, and 3Christoph Dornier Foundation of Clinical Psychology, Marburg, German)' (Received 30 September 1993; received for publication 7 January 1994) Summary--Results on cardiac awareness in panic disorder are inconsistent. The present study attempted to clarify whether differences in instructions or the inclusion of patients taking antidepressant medication could account for these inconsistencies. 112 patients with panic disorder with agoraphobia were compared to 40 normal controls on the heartbeat perception task developed by Schandry (1981) [Schandry, R., Psychophysiology, 18, 483-488] using a standard instruction ("count all heartbeats you feel in your body") and a strict instruction ("count only those heartbeats about which you are sure"). Superior heartbeat perception for patients was only found with the standard instruction. Similarly, only with the standard instruction, patients taking medication affecting the cardiovascular system performed worse than patients without medication, as expected based on the relationship between stroke volume and heartbeat perception. The pattern of group differences indicates that agoraphobic patients have a better feeling for how fast their heart is beating than controls although these differences may be due to a tendency to interpret weak sensations as heartbeats. Furthermore, we tested in a subgroup of 40 patients whether cardiac awareness changes with exposure treatment. No changes in heartbeat perception were observed.
INTRODUCTION Palpitations are among the most common symptoms of panic attacks (Barlow, 1988; Margraf, Taylor, Ehlers, Roth & Agras, 1987). This has led researchers to raise the question of whether patients with panic disorder are better at perceiving their heartbeats than other people (see Ehlers, 1993, for a review). As Ehlers, Margraf and Roth (1988a) have hypothesized, such an increased cardiac awareness would be neither a necessary nor sufficient cause for panic attacks but--for those patients with good heartbeat perception--this factor could be involved in the development or maintenance of the disorder by increasing the probability of cardiac sensations which may trigger panic attacks if interpreted as threatening or by motivating the patient to avoid situations in which these sensations occur. Empirical studies on heartbeat perception in panic disorder have given inconsistent results. While some studies found greater cardiac awareness in patients with panic disorder (Ehlers & Breuer, 1992; Harbauer-Raum, 1987), the majority have yielded negative findings (e.g. Ehlers, Margraf, Roth, Taylor & Birbaumer, 1988b; Hartl, 1992). The purpose of the present paper is, first, to investigate whether methodological differences could have contributed to these inconsistencies, and second, to investigate whether cardiac awareness changes with treatment. Several studies have required the Ss to compare an external signal (series of tones) with the rhythm of their heartbeats. All these studies failed to find differences between panic disorder patients and controls no matter whether Ss had to adjust the rate of the stream of tones to their heart rate (Ehlers et al., 1988b) or had to distinguish between accurate and false feedback according to the discrimination paradigms of Katkin (Katkin, 1985; Ehlers, 1988) or Whitehead (Whitehead, Drescher, Heiman & Blackwell, 1977; Asmundson, Sandler, Wilson & Norton, 1993). One possible explanation for the lack of group differences with these paradigms is that the external signal may have distracted Ss from their internal cues (Pennebaker, 1982). Fur:hermore, the comparison of an external and internal signal may be much more difficult than the perception of an internal signal. This is in line with the fact that untrained Ss perform at chance levels in discrimination paradigms of heartbeat perception (Katkin, 1985). In the study of Asmundson et al. (1993), only male nonpanickers performed better than chance. Ehlers and Breuer (1992) have argued that the major question of interest to the study of panic disorder is how well patients can perceive whether their heart is beating fast or slow and whether they can detect arrhythmias, as these events may trigger panic attacks or motivate patients to avoid situations in which these sensations occur. This question cannot be answered with discrimination paradigms because these paradigms involve feedback on the rhythm of heartbeats. Increased accuracy in heartbeat perception in cardiac neurotics (Harbauer-Raum, 1987) and patients with panic disorder (Ehlers & Breuer, 1992) compared to normal controls was found with the mental-tracking paradigm developed by Schandry (1981). Subjects are required to count their heartbeats silently during signaled intervals without taking their pulse. This paradigm has a high face validity for the clinically important question of whether panic disorder patients have a good feeling for how fast their heart is beating. However, this paradigm has been criticized on the grounds that Ss may give spuriously correct answers without feeling their heartbeats if they estimate the time interval correctly and calculate the number of heartbeats from general knowledge of their heart rate (Montgomery & Jones, 1984). According to results of *To whom all correspondence should be addressed at: Department of Psychiatry, University of Oxford, Warneford Hospital, Oxford OX3 7JX, U.K. 69
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CASEHISTORIESAND SHORTERCOMMUNICATIONS
Ehlers and Breuer (1992, study 2), this interpretation is unlikely, because Ss performed much worse in a time estimation task than in the heartbeat perception task. Time intervals were usually overestimated, whereas the number of heartbeats was underestimated by the vast majority of Ss. Underestimation is to be expected if Ss are actually counting their heartbeats but miss a few beats because of inaccurate perception. Whereas Knoll, Folten and Hodapp (1991) reported a small marginally significant correlation between time estimation and performance in the mental-tracking task in non-anxious women (r = 0.20, P < 0.06), Ehlers and Breuer (1992) did not find such correlation. Antony, Meadows, Brown and Barlow (1993b) found a negative correlation (r = -0.48, P = 0.07). Overall, these results suggest that Ss do not simply estimate time intervals during the mental-tracking task. Two recent studies, however, did not replicate the superior performance of panic disorder patients in the mental-tracking paradigm (Antony, Brown, Craske, Barlow, Mitchell & Meadows, 1993a; Hartl, 1992). Several details of methodology may have contributed to these discrepant findings. One possibility concerns sample differences. First, differences in sample size may have resulted in different statistical power. Means in the Antony et al. (1993a, b) study pointed in the same direction as in the Ehlers and Breuer (1992) studies, but the group differences were not significant. However, the means in the Hartl (1992) study pointed in the opposite direction. One possible explanation for this result is that Hartl's controls had a lower body mass index than the patients and that slightly (nonsignificantly) more men were included in the control sample (45%) than in the patient sample (38%). Previous research has shown that female sex and obesity are associated with poorer heartbeat perception (see Ehlers & Breuer, 1992, for a summary). In the Ehlers and Breuer (1992) and Antony et al. (1993a) studies, patient and control groups were matched for sex, body mass index, and physical activity. In addition, the studies differed in the proportion of agoraphobic Ss included. Ehlers and Breuer (1992) found that patients with agoraphobia show a better heartbeat perception than patients with no avoidance. The Ehlers and Breuer sample included only 13.8% of patients without agoraphobic avoidance, compared to 24% in the Hartl (1992) sample. The Antony et al. (1993a, b) sample did not include any Ss with severe agoraphobia compared to 13.8% in the Ehlers and Breuer (1992) sample. It is possible that increased cardiac awareness is restricted to those patients with agoraphobic avoidance. Another difference between the studies that is of interest to the present paper is the inclusion of Ss taking medication. While Ehlers and Breuer (1992) excluded all S s who took medication affecting the cardiovascular system including tricyclic antidepressants, the panic disorder sample of Antony et al. (1993a, b) included 10% Ss on antidepressants. Hartl (1992) instructed patients not to take any medication on the test day. However, 24% had been regularly taking antidepressants on previous days. The inclusion of Ss on antidepressants is problematic because these drugs increase mean heart rates by about 15 bpm (Roth, Margraf, Ehlers, Haddad, Maddock, Davies, Agras & Taylor, 1992). Subjects with higher heart rates show a larger error in Schandry's heartbeat perception paradigm. Ehlers and Breuer found a correlation of r = 0.23 (P < 0.001) and Antony et al. (1993a, b) a correlation of r = 0.39 (P < 0.01) between heart rate and error scores. This relationship is probably mediated by the fact that accuracy in heartbeat perception depends on cardiac output. Schandry, Bestler and Montoya (1993) found a correlation of r = 0.59 between stroke volume and performance in the heartbeat perception task. Although not explicitly mentioned by Hartl (I 992), her instructions differed from those used by Ehlers and Breuer (1992; Hartl, personal communication, 1989). While Ehlers and Breuer told Ss to count the number of heartbeats they felt in their body, Hartl (1992) gave a stricter instruction and emphasized that the Ss should not make any guesses but should only count heartbeats they had really felt. This difference in instruction may have influenced the results in that it made Ss less likely to report a heartbeat in the Hartl study, resulting in much higher average error scores (for patients, sitting condition: approximately 58%, for controls approximately 44%--compared to 22 and 30% in the Ehlers and Breuer study, respectively). Hartl (1992) found that panic patients were more often unable to feel any heartbeat during a trial than controls. They were also less confident about their judgements than controls. However, the patient group showed a higher correlation between subjective confidence of perception and error in the heartbeat perception task (r = -0.76) than controls (r = -0.37) which would indicate a more realistic heartbeat perception in the patient group. It is possible that Hartl's patients experienced more performance anxiety than controls because Ss were tested in a clinical setting as a part of several heartbeat monitoring procedures run by a physician (Dr Hartl). Tests of their heart have a high relevance to panic disorder patients. This might have negatively affected their performance in this study. Also, the strict instruction may have made them more worried about erroneously reporting a beat that did not occur which would result in underreporting of heartbeats. In contrast, the Ss in the Ehlers and Breuer study were not tested in a clinical setting and this--together with the less strict instructions--possibly affected their state anxiety levels. Compared to patients' mean trait anxiety levels of 43.8 on the STAI-scale, the state anxiety levels of 49.4 in Hartl's study are high. This compares to a mean trait anxiety level of 51.7 in the Ehlers and Breuer study and a mean state anxiety of 44.6. Hartl (1992) found a correlation between state anxiety and poor heartbeat perception in panic patients (r = 0.26, < 0.10) whereas Ehlers and Breuer (1992) did not find such a correlation. The present study was designed to investigate the possible contribution of these methodological differences to the discrepant results. First, we wanted to clarify the influence o f instructions on comparisons between panic disorder patients and controls on Schandry's heartbeat perception paradigm. We compared the performance of agoraphobic patients and controls when using the instructions previously used by Ehlers and Breuer (1992) and when using a very strict instruction asking the Ss not to count any heartbeats about which they were not absolutely sure. Furthermore, we explored whether patients taking medication affecting their cardiovascular system differ in their heartbeat perception from patients without medication. These differences might be expected based on the correlations between stroke volume and heartbeat perception. In addition, we were interested in whether heartbeat perception changes with treatment. If heightened cardiac awareness is primarily a function of heightened anxiety, as Antony et al. (1993b) have suggested, patients' performance in the heartbeat perception test should deteriorate with successful treatment. The same result would be expected if superior heartbeat perception in panic disorder patients is primarily due to increased attention to internal cues based on their interoceptive fears. On the other hand, exposure therapy may enhance cardiac awareness because exposure induces cardiac sensations such as palpitations and thus might train Ss in heartbeat perception. Finally, heartbeat perception may be a relatively stable individual characteristic which is not influenced by treatment. Ehlers and Breuer (1992) did not find any differences in heartbeat perception between patients with current panic attacks and those in remission.
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METHOD
Subjects Comparison of patients and controls. Patients with the DSM-III-R diagnosis of panic disorder with agoraphobia (N = 112) were recruited through the outpatient clinic o f the Christoph Dornier Foundation o f Clinical Psychology, Marburg, Germany. The clinic specializes on exposure therapy for anxiety disorders. Patients were interviewed by trained psychologists using the German version of the Anxiety Disorders Interview Schedule-Revised (ADIS, DiNardo & Barlow, 1988; German version: Diagnostisches Interview bei psychischen Sttrungen, DIPS, Margraf, Schneider, Ehlers, DiNardo & Barlow, 1991). Patients on medication affecting the cardiovascular system (e.g. tricyclic antidepressants, beta-blockers, or hypertensive medication) were excluded. Controls (N = 40) were recruited through advertisements in local newspapers and received 10 German Marks for their participation. They were matched to the patient group for sex and were to be comparable in age and body mass index, and had never experienced panic attacks or suffered from any psychiatric disorder according to the DIPS. Table I gives a description of the groups in terms of sex, age, body mass index, trait anxiety, as measured by the State-Trait-Anxiety Inventory (STAI-trait and STAI-state, Spielberger, Gorsuch & Lushene, 1970; German version, Laux, Glanzmann, Schaffner & Spielberger, 1981); depression, as measured by the Beck Depression Inventory (BDI, German version: Beck, Rush, Shaw & Emery, 1981); and degree of agoraphobic avoidance behavior, as measured by the Mobility Inventory (MI) scales Alone for avoidance when alone and Accompanied for avoidance when accompanied by a trusted companion (Chambless, Caputo, Jasin, Gracely & Williams, 1985; German version: Ehlers, Margraf & Chambless, 1993). Patients and controls did not differ in their sex, age, or body mass index. Patients had significantly higher trait and state anxiety, depression, and agoraphobic avoidance than controls. Comparison of patients with and without medication. Twenty-four additional patients (17 women, 7 men) were tested. They met DSM-III-R criteria for panic disorder with agoraphobia according to the DIPS. These patients had to be excluded from the patient group described above because they were taking medication affecting the cardiovascular system. To explore the possible effects of medication on performance in the heartbeat perception test, 107 patients (77 women, 30 men) who were not taking medication affecting the cardiovascular system were matched to the 24 patients on medication based on their sex and body mass index. Patients with and without medication did not differ in terms of age [t (129) = 1.16, P > 0.25], sex [12(l) = 0.01, P > 0.91], body mass index [t(129) = 0.27, P > 0.78], trait anxiety [t(104) = 0.24, P > 0.81], state anxiety [t(106) = 0.48, P > 0.63], depression [t(112) = 0.36, P > 0.72] or avoidance [MI-alone: t(112) = 0.44, P > 0.65; MI-accompanied: t(112) = 0.54, P > 0.58]. Patients before and after therapy. Forty of the agoraphobic patients (27 women, 13 men) who were not taking medication affecting the cardiovascular system were tested again after the end of treatment. This sample had a mean age of 36.1 years (SD = 9.5) and a mean body mass index of 23.0 (SD = 2.9). The treatment involved massed therapist-assisted and self-guided exposure to feared situations. Details of the treatment program are found in Fiegenbaum (1988). Mean duration of treatment was 32 h (SD: 7.5 h), including initial interviews and assessment. As shown in Table 2, treatment led to significant reductions in agoraphobic avoidance, anxiety and depression. Number of panic attacks also decreased during therapy. Note that the number of panic attacks at the end of treatment includes those occurring during the last month of treatment.
Heartbeat perception paradigm Heartbeat perception was assessed with the mental-tracking paradigm developed by Schandry (1981). Subjects were instructed to silently count their heart beats during signaled intervals of 35, 25 and 45 sec without taking their pulse or using any other strategies such as holding their breath. During each of the trials, Ss were first presented with a warning stimulus (800 Hz, 65 dB, 100 msec) preparing them for the trial. The warning stimulus was given 500 msec after a R-wave of the S's electrocardiogram. The start signal (1000 Hz, 65 dB, 50 msec) was triggered immediately after the third R-wave following the warning stimulus. The tone signaling the end of the counting period (1000 Hz, 65 dB, 50 msec) was given when the interval of 35, 25, or 45 sec was up and 300 msec after the last R-wave had elapsed. The computer program determined the number of R-waves occurring during the counting interval. Three blocks of three trials o f the mental tracking paradigm were run. For the first two blocks, Ss received the standard instruction used by Ehlers and Breuer (1992) to count all the heartbeats they felt in their body. During one of the blocks, a distracting series of tones was given while Ss were counting their heartbeats. The tones had a volume of 70 dB and frequencies between 80 and 170 Hz. Frequencies were randomly given with the restriction of a minimum difference of 10 Hz between consecutive tones. The inter-tone-interval was 600 msec. This block was run to investigate the possible effects of distracting external signals on Ss' performance in the mental tracking paradigm. The two trials with the standard instruction with and without distracting tones were presented in balanced order. In the third block, Ss were given the very strict instruction to only count the heartbeats that they had really felt in their body.They were asked to refrain from counting any heartbeats about which they were not sure and which would represent an estimated heartbeat rather than one really felt. After each trial, Ss were asked to rate the confidence with which they had felt their heartbeats on a scale between 0 "totally uncertain" to 10 "totally certain". Table 1. Patient and control samples
Age (years) Sex Women Men Body Mass Index STAI-trait -state BDI MI-alone -accompanied
Patients (N = 112)
Controls (N = 40)
36.3 (7.7) N = 76 (67.9%) N = 36 (32.1%) 23.7 (3.0) 53.9 (9.9) 51.9 (12.4) 16.6 (8.5) 3.23 (I.01) 2.26 (0.87)
36.4 (9.1) N = 27 (67.5%) N = 13 (32.5%) 22.6 (3.8) 32.8 (7.1) 31.7 ( 7 . 8 ) 2.7 ( 2 . 9 ) 1.17 (0.24) 1.06 (0.15)
T-test or ;(2-test t(150) = 0.12, NS ~2(1) = 0.002, NS t(55.51) = t(87.05) = t(107.15)= t(130.13)= t(117.93)~ t(108.59)=
If not indicated otherwise, the table shows means (standard deviations). BRT 331--F
1.63, NS 13.28, P < 0.001 11.14, P < 0.001 14.09, P < 0.001 18.68, P < 0.001 13.02, P < 0.001
72
CASE HISTORIESAND SHORTERCOMMUNICATIONS Table 2. Questionnaire scores of 40 patients before and after treatment
STAl-trait -state BDI Ml-alone -accompanied Panic attacks/ month
Before treatment
After treatment
52.4 (9.6) 50.4 (10.0) 15.0 (8.4) 3.25 (1.14) 2.33 (0.97)
44.3 (9.4) 40.0 (9.5) 7.1 (5.9) 1.63 (0.61) 1.27 (0.28)
I 1.1 (18.2)
4.0 (8.0)
t -Test t(21) t(21) t(23) t(35) t(35)
= ~ = = =
4.59, 4.55, 6.26, 9.83, 6.83,
P P P P P
< < < < <
0.001 0.001 0.001 0.001 0.001
t(28) = 2.06, P < 0.05
Protocol Patients o f the Christoph Dornier Foundation of Clinical Psychology were diagnosed with the DIPS (Margraf et aL, 1991). During the baseline assessment before treatment they answered questionnaires, received a medical cheek-up and participated in the heartbeat perception test. For the test day, S s were instructed to abstain from alcohol, to eat just a light meal, not to smoke more than usual and not to drink more caffeine-containing beverages than usual. After electrodes had been attached, S s were asked to take off their watches for the duration of the test. For each of the blocks of the heartbeat perception paradigm, S s received written instructions. The experimenter answered possible questions, and then demonstrated the different signals. A short test trial of 12 see was run to check whether Ss had understood the task. Each block consisted of three trials of the mental tracking paradigm lasting 35, 25, and 45 see. During the tasks, Ss sat alone in a comfortable arm chair. They could not see the experimenter, but could communicate with her or him via intercom. T h r o u g h a one-way mirror, the experimenter checked whether Ss complied with the instruction not to take their pulse during the heartbeat perception task. A subgroup of 40 patients was tested again with the same protocol after the end of exposure treatment. Assessment Degree of inaccuracy in heart beat perception was defined as the modulus o f actual number of heart beats minus counted heart beats, divided by actual heart beats and multiplied by I00 to express as a percentage i.e. lAB -
-
CBI
-
x
AB
100
where AB = actual beats and CB = counted beats. Mean error scores were obtained from the average of the three trials for each of the three blocks. Schandry (1985) argued that percent error scores are superior to simple difference scores as Ss with higher heart rates have a greater chance of missing heart beats during the counting interval. For example, if Ss A and B both feel every second heart beat, and subject A has a heart rate of 50 while subject B has a heart rate o f I00, the difference between the n u m b e r of counted beats and the number of real heart beats is 100% higher in S B than in S A whereas their performance is regarded equivalent according to Schandry's analysis. All significance levels are two-tailed. RESULTS
Comparison o f patients and controls The results of the three blocks of the heartbeat perception test are found in Table 3. Table 3 also shows the Ss' mean heart rates for each of the blocks. Based on the results of the previous studies of Ehlers and Breuer (1992) and Hartl (1992), the following hypotheses for the mean error in heartbeat perception were evaluated by planned comparisons. Table 3. Heart rates and heartbeat perception of patients and controls means (standard deviations)
Heart rate (bpm) Experimental condition Standard instruction Standard instuction with distraction Strict instruction
Patients (N = 112)
Controls (N = 40)
t-Test
79.8 (13.7)
71.3 (11.5)
t(150) ffi 3.54, P < 0.001
73.2 (12.8) 77.7 (11.8)
65.1 (9.9) 70.5 (9.9)
t(150) = 3.64, P < 0.001 t(150) = 3.45, P < 0.001
Error in heartbeat perception (% heart rate) Experimental Patients Controls condition (N = 112) (N = 40) Standard instruction 27.6 (21.6) 35.1 (25.0) Standard instruction with distraction 30.1 (20.4) 38.9 (29.5) Strict instruction 62.0 (32.6) 67.6 (30.7) Confidence rating (0-10) Experimental Patients Controls condition (N = 94) (N = 37) Standard instruction Standard instruction with distraction Strict instruction NS = nonsignificant.
ANCOVA F(I,149) = 4.43, P < 0.05 F(I,149) = 5.73, P < 0.05 F(I, 149) = 1.07, NS
t-Test
5.62 (2.32)
5.89 (2.49)
t(129) =0.59, NS
4.61 (2.34) 5.92 (2.49)
6.00 (2.44) 7.05 (2.44)
t(129) = 3.04, P < 0.01 t(129) = 2.35, P < 0.05
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Table 4. Percentage of subjects who could not feel any heartbeat Experimental condition
Trial
Standard instruction
Patients Controls (N = 112) (N = 40)
I 2 3 1 2 3 I 2 3
Standard instruction with distraction Strict instruction
0.9 2.7 1.8 0.9 0.9 1.8 22.3 16.1 18.0
10.0 7.5 10.0 7.5 10.0 12.5 30.0 22.5 25.0
Fisher's exact/~2tests P < 0.05 NS P < 0.05 P < 0.06 P < 0.05 P < 0.05 NS NS NS
NS = nonsignificant.
• Patients show a higher accuracy of heartbeat perception (lower error score) than controls if the standard instruction is used (Ehlers & Breuer, 1992). • No group differences are found if a very strict instruction is used (Hartl, 1992). Since the patient group showed significantly higher heart rates and since heart rate and error in heartbeat perception are positively correlated, we used ANCOVAs with heart rate as the covariate to evaluate group differences. The results are in line with the hypotheses. Patients showed a lower error score in the mental tracking paradigm only with the standard instruction, not with the very strict instruction. The two standard instruction blocks with and without distraction both showed differences between the groups. Hartl's (1992) observation that panic disorder patients may be less certain about their heartbeats was evaluated first by comparing the mean confidence ratings for each of the blocks (t-tests) and by calculating the number of Ss for each trial who could not feel any heartbeats (Table 4). For the standard instruction block without distraction (equivalent to the protocol of Ehlers & Breuer, 1992) patients and controls did not differ in their confidence of heartbeat perception. In the other two blocks (standard instruction with distraction, strict instruction) patients were less certain about their heartbeats as also reported by Hartl (1992). Patients with better heartbeat perception gave higher confidence ratings for standard instruction conditions (without distraction: r = -0.21, P < 0.05; with distraction: r = -0.25, P < 0.05). For controls, these correlations were in the opposite direction (without distraction: r =0.15, NS; with distraction: r =0.30, P <0.10). Differences in correlation between patients and controls tended to be significant (without distraction: P <0.10; with distraction: P < 0.001). No correlation between performance and confidence was found for the strict instruction condition in either group. Hartl's observation that panic disorder patients are more likely than controls not to feel any heartbeat at all was not replicated. On the contrary, for the standard instruction trials more controls than patients tended to be unable to feel their heartbeats.
Comparison o f patients with and without medication Table 5 presents the comparisons of patients who were and those who were not taking medication affecting the cardiovascular system. In the standard instruction block without distraction, patients on medication had higher error scores in heartbeat perception than those without medication. A similar trend was observed in the standard instruction block with distracting tones. The strict instruction condition did not yield group differences. No group differences were observed for confidence ratings or heart rates.
Table 5. Comparison of patients with and without medication means (standard deviations)
Heart rate (bpm) Experimental condition Standard instruction Standard instruction with distraction Strict instruction
Without medication (N = 107)
With medication (N = 24)
t-Test
80.4 (13.7)
82.9 (14.4)
t(129) = 0.81, NS
73.7 (13.0) 78.1 (11.9)
76.0 (12.6) 80.8 (13.8)
t(129) = 0.80, NS t(129) = 0.96, NS
Error in heartbeat perception (% heart rate) Experimental condition Standard instruction Standard instruction with distraction Strict instruction
Without medication (N = 107)
With medication (N = 24)
28.7 (21.7)
39.9 (29.8)
t(129) = 2.12, P <0.05
30.6 (20.4) 63.2 (33.0)
40.0 (28.8) 68.4 (30.9)
t(129) = 1.88, P < 0.07 t(129) = 0.71, NS
Without medication (N = 107)
With medication (N = 24)
t -Test
5.73 (2.47)
6.46 (2.09)
t(ll0) = 1.26, NS
4.63 (2.40) 6.06 (2.64)
5.59 (2.33) 6.35 (2.97)
t(ll0) = 1.65, NS t(110) = 0.44, NS
t-Test
Confidence rating (0-10) Experimental condition Standard instruction Standard instruction with distraction Strict instruction NS = nonsignificant.
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CASE HISTORIES A N D SHORTER COMMUNICATIONS
Table 6. Comparison of 40 patients before and after exposure treatment means (standard deviations) Heart rate (bpm) Experimental Before After condition treatment treatment t-Test Standard instruction Standard instruction with distraction Strict instruction
81.8 (14.7)
83.2 (16.9)
t(39) = -0.51, NS
75.6 (13.8) 80.4 (13.6)
76.3 (15.7) 82.7 (15.8)
t(39) = -0.25, NS t(39) = -0.80, NS
Error in heartbeat perception (% heart rate) Experimental Before condition treatment
After treatment
t-Test
Standard instruction Standard instruction with distraction Strict instruction
27.9 (21.1)
32.0 (22.0)
t(39) = -1.30, NS
29.1 (20.3) 62.4 (31.8)
30.2 (24.1) 63.6 (32.7)
t(39) = -0.35, NS t(39) = -0.25, NS
Confidence rating (0-10) Experimental condition
Before treatment
After treatment
5.32 (2.43)
5.47 (2.34)
t(26) = -0.32, NS
4.73 (2.08) 6.05 (2.28)
4.47 (2.36) 5.80 (2.49)
t(26) = 0.77, NS t(26) = 0.53, NS
Standard instruction Standard instruction with distraction Strict instruction
t-Test
NS = nonsignificant.
Patients before and after therapy
Table 6 gives the results o f the heartbeat perception tests before and after treatment. No changes in heartbeat perception, heart rate, or confidence ratings were observed. Correlations between the two tests were r = 0.58, r = 0.57, and r = 0.64 for the standard instruction conditions without and with distraction, and the strict instruction condition, respectively (all P's < 0.001).
DISCUSSION The study replicated the apparently contradictory pattern of group differences between panic patients and normal controls previously reported by Ehlers and Breuer (1992) and Hartl (1992): When the instruction "count the heartbeats you feel in your body" was used, panic disorder patients with agoraphobia showed a better heartbeat perception than controls and had the same level of confidence in their perceptions. When the instruction "count the heartbeats that you really feel and about which you are sure" was used, no group differences in accuracy were found, but patients were less certain about their perception than controls. This pattern of results indicates that agoraphobic patients have a better general feeling for how fast their heart is beating than controls. Group differences in correlations between performance in the mental-tracking task and confidence ratings found in Hartrs (1992) and the present study further indicate that patients tend to have more realistic perceptions of their accuracy than controls. On the other hand, confidence ratings showed that patients can be more easily made uncertain by distraction or strict instructions than controls. The latter could be related to the fact that patients are more worried about their heart and probably attach more significance to the test results than controls, This is especially the case if Ss are tested in a clinical setting like in Hartrs (1992) or the present study. The difference o f patients taking medication and those not taking medication in the standard instruction conditions underscores the validity of the group differences found with this paradigm. Patients taking medication affecting the cardiovascular system were less accurate in perceiving their heartbeats than those without medication. The strict instruction condition probably yields floor effects and is not sensitive enough to show group differences in cardiac perception. The effect of medication on heartbeat perception needs to be confirmed with different designs such as studying patients before and after they start taking medication. We cannot rule out that effects of self-selection contributed to the present finding. Patients with poor interoception may tolerate the side effects o f medication such as tricyclic antidepressants better than patients with good interoception. The present results also show limitations of the heartbeat tracking paradigm in assessing Ss' ability to perceive their heartbeats. Instructional sets had large effects on the number of heartbeats which Ss counted. However, it is highly unlikely that Ss in the standard instruction condition reported heartbeats without any corresponding sensation (false alarms). The vast majority o f Ss, patients as well as controls, reported fewer heartbeats than had actually occurred. This pattern is to be expected if Ss count their heartbeats but miss a few because of inaccurate perception. In the rare cases that Ss overestimated the number of heartbeats only very few additional heartbeats were reported. Further findings support the validity o f the standard instruction paradigm: The differences between patients taking medication affecting the cardiovascular system and those without medication, the high correlations between stroke volume and test results reported by Schandry et al. (1993), and the lack o f correlations between accuracy of time estimation and performance in the heartbeat perception task reported by Ehlers and Breuer (1992), and relationship of good heartbeat perception and maintenance of panic attacks in a prospective one year follow-up study (Ehlers, in press). Therefore it is highly unlikely that Ss just guess the number of heartbeats during the standard instruction paradigm. However, it is possible that panic disorder patients and controls differ in their tendency to think that a heartbeat has occurred when the corresponding sensation is rather weak. Both a tendency to interpret weak sensations as heartbeats as well as differences in ability to discriminate heartbeats would have the effect that panic patients tend to feel more of their heartbeats than controls. This could feed into the vicious cycle culminating in a panic attack (Clark, 1986; Ehlers et al., 1988a) or motivate the patient to
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avoid exciting, anxiety-provoking or strenuous activities and situations. This interpretation is supported by our finding that heartbeat perception measured with the standard instruction predicts relapse in panic patients in remission and maintenance of panic attacks in infrequent panickers and treated panic patients (Ehlers, in press). The lack of differences and relatively high correlations of heartbeat perception scores before and after treatment indicates that heartbeat perception is a relatively stable individual characteristic which is not influenced in a systematic way by exposure treatment. Similar results were recently reported by Antony et al. (1993b). This group compared 15 patients with panic disorder before and after cognitive-behavioral treatment. This lack of changes with treatment is in line with our previous finding that patients with current panic attacks do not differ from those in remission (Ehlers & Breuer, 1992). Therefore, it is unlikely that increased cardiac awareness is a function of heightened anxiety per se.
Acknowledgements--The research described in this paper was supported by a grant from the Deutsche Forschungsgemeinschaft (Eh 97/1-4). We would like to thank Kathrin Kluwe and Monika Freitag for their help. Anke Ehlers is supported by a Wellcome Principal Fellowship.
REFERENCES
American Psychiatric Association (1980). Diagnostic and Statistical Manual of Mental Disorders, Third Edition (DSM-III). Washington, D.C.: American Psychiatric Press. American Psychiatric Association (1987). Diagnostic and Statistical Manual of Mental Disorders, Third Edition-Revised (DSM-III-R). Washington, D.C.: American Psychiatric Press. Antony, M. M., Brown, T. A., Craske, M. G., Barlow, D. H., Mitchell, W. B. & Meadows, E. A. (1993a). Accuracy of heart beat perception in panic disorder, social phobia, and non-anxious subjects. Submitted. Antony, M. M., Meadows, E. A., Brown, T. A. & Barlow, D. H. (1993b). Cardiac awareness before and after cognitive-behavioral treatment for panic disorder. Submitted. Asmundson, G. J. G., Sandier, L. S., Wilson, K. G. & Norton, G. R. (1993). Panic attacks and interoceptive acuity for cardiac sensations. Behaviour Research and Therapy, 31, 193-197. Barlow, D. H. (1988). Anxiety and its disorders. New York: Guilford Press. Beck, A. T., Rush, A. J., Shaw, B. F. & Emery, G. (1981). Kognitive Therapie der Depression. Miinchen: Urban & Schwarzenberg. Brener, J. & Kluvitse, C. (1988). Heartbeat detection: Judgements of the simultaneity of external stimuli and heart beats. Psychophysiology, 25, 554-561. Chambless, D. L., Caputo, G. C., Jasin, S. E., Gracely, E. J. & Williams, C. (1985). The Mobility Inventory for agoraphobia. Behaviour Research and Therapy, 23, 35-44. Clark, D. M. (1986). A cognitive approach to panic. Behaviour Research and Therapy, 24, 461-470. DiNardo, P. A. & Barlow, D. H. (1988). Anxiety Disorders Schedule--Revised (ADIS-R). Albany, N.Y.: Graywind. Ehlers, A. (1988). Interozeption and selektive Aufmerksamkeit bei Personen mit Panikanfiillen. Unpublished research report, German Research Foundation. Ehlers, A. (1993). Interoception and panic disorder. Advances of Behaviour Research and Therapy, 15, 3-21. Ehlers, A. (in press). Factors associated with the maintenance of panic attacks: a one-year prospective study. Journal of Abnormal Psychology. Ehlers, A. & Breuer, P. (1992). Increased cardiac awareness in panic disorder. Journal of Abnormal Psychology, 101, 371-382. Ehlers, A., Margraf, J. & Chambless, D. L. (1993). Fragebogen zu k6rperbezogenen Angsten, Kognitionen und Vermeidung. Weinheim: Beltz. Ehlers, A., Margraf, J. & Roth, W. T. (1988a). Selective information processing, interoception, and panic attacks. In Hand, I. & Wittchen, H. U. (Eds), Panic and phobias 2 (pp. 129-148). Berlin: Springer. Ehlers, A., Margraf, J., Roth, W. T., Taylor, C. B. & Birbaumer, N. (1988b). Anxiety induced by false heart rate feedback in patients with panic disorder. Behaviour Research and Therapy, 26, l-I 1. Fiegenbaum, W. (1988). Long-term efficacy of ungraded versus graded massed exposure in agoraphobia. In Hand, I. & Wittchen, H. U. (Eds.), Panic and phobias 2 (pp. 83-88). Berlin: Springer. Harbauer-Raum, U. (1987). Wahrnehmung von Herzschlag und Herzarrhythmien--Eine Labor-Feldstudie an Patienten mit Herzphobie. In Nutzinger, D. O., Pfersmann, D., Welan, T. & Zapotoczky, H. G. (Eds), Herzphobie (pp. 84-91). Stuttgart: Enke. Hartl, L. A. (1992). Die Panikstb'rung. Eine Untersuchung zur Rolle der Wahrnehmung yon K6rperprozessen. Frankfurt: Peter Lang. Katkin, E. S. (1985). Blood, sweat, and tears: Individual differences in autonomic self-perception. Psychophysiology, 22, 125-137. Knoll, J. F., Folten, A. & Hodapp, V. (1991). Heart rate perception ability: A comparison of two methods. Journal of Psychophysiology, 5, 113. Laux, L., Glanzmann, P., Schaffner, P. & Spielberger, C. D. (1981). Das State-Trait Angstinventar. Weinheim: Beltz. Margraf, J., Schneider, S., Ehlers, A., DiNardo, P. & Barlow, D. H. (1991). Diagnostisches Interview bei psychischen Stdrungen (DIPS). Berlin: Springer. Margraf, J., Taylor, C. B., Ehlers, A., Roth, W. T. & Agras, W. S. (1987). Panic attacks in the natural environment. Journal of Nervous and Mental Disease, 175, 558-565. Montgomery, W. A. & Jones, G. E. (1984). Laterality, emotionality, and heartbeat perception. Psychophysiology, 21, 459-465. Pennebaker, J. W. (1982). The psychology of physical symptoms. New York: Springer. Roth, W. T., Margraf, J., Ehlers, A., Haddad, J. M., Maddock, R. J., Davies, S., Agras, W. S. & Taylor, C. B. (1992). Imipramine and alprazolam effects on stress reactivity in panic disorder. Biological Psychiatry, 27, 1231-1243. Schandry, R. (1981). Heart beat perception and emotional experience. Psychophysiology, 18, 483-488.
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Schandry, R., Bestler, M. & Montoya, P. (1993). On the relationship between cardiodynamics and heartbeat perception. Psychophysiology, 30, 467-475. Spielberger, C. D., Gorsuch, R. L. & Lushene, R. E. (1970). State-trait anxiety inventory. Palo Alto, CA: Consulting Psychologists Press. Whitehead, W. E., Drescher, V. M., Heiman, P. & Blackwell, B. (1977). Relation of heart rate control to heartbeat perception. Biofeedback and Self-Regulation, 2, 371-392.