The Language of Medically Unexplained Dyspnea

CHEST

Original Research DYSPNEA

The Language of Medically Unexplained Dyspnea* Jiangna Han, MD, FCCP; Yuanjue Zhu, MD; Shunwei Li, MD; Jian Zhang, MD; Xiansheng Cheng, MD; Omer Van den Bergh, PhD; and Karel P. Van de Woestijne, MD

Background: Medically unexplained dyspnea (MUD) refers to a condition characterized by a sensation of dyspnea and is typically applied to patients presenting with anxiety and hyperventilation without cardiopulmonary explanations for their dyspnea. The diagnosis is difficult. We investigated whether descriptors of dyspnea and associated symptoms of MUD are differentially diagnostic. Methods: A respiratory symptom checklist incorporating 61 spontaneously reported descriptors of dyspnea was administered to 96 patients with MUD and 195 patients with cardiopulmonary diseases. Symptom factors measuring different qualitative aspects of dyspnea were derived by a principal component analysis. The separation of two patient groups in terms of symptom factors was achieved by a discriminant analysis. Results: Five factors grouped different attributes of dyspnea: urge to breathe, depth and frequency of breathing, difficulty breathing and phase of respiration, wheezing, and affective dyspnea. The other five factors grouped symptoms of anxiety, tingling, cough and sputum, palpitation, and out of control. A discriminant analysis allowed to separate two patient groups (R2 ⴝ 0.45, p < 0.0001). The presence of urge to breathe, affective dyspnea, anxiety, and tingling pointed to the diagnosis of MUD, whereas the reporting of wheezing, cough and sputum, and palpitation indicated cardiopulmonary diseases. The sensitivity was 85%, and specificity was 88%. Conclusions: Descriptors of dyspnea and associated symptoms allows satisfactory separation of patients with MUD from patients with cardiopulmonary diseases. A prospective study will be required to test the validity and predictive values of the descriptor model in another cohort of patients. (CHEST 2008; 133:961–968) Key words: descriptors of breathlessness; diagnosis; dyspnea; factor analysis Abbreviation: MUD ⫽ medically unexplained dyspnea

unexplained dyspnea (MUD) refers to a M edically condition characterized by a sensation of dyspnea and is typically applied to patients presenting with anxiety and hyperventilation without underlying cardiopulmonary explanations for their dyspnea.1–9 Several terms have been proposed to classify the patients, the most frequently used being hyperventilation syndrome1,2 or idiopathic hyperventilation,3,4 medically unexplained dyspnea,5,6 or behavioral dyspnea,7,8 and anxiety disorders.9 MUD is fairly common in medical outpatients,5,10 but physicians seem to have considerable discomfort in managing these patients. Any patient whose dyspnea cannot be explained raises the concern of “what am I missing?” As a www.chestjournal.org

consequence, many such patients undergo extensive and unproductive investigations. An experienced physician often feels he can diagnose MUD relying on patient history and symptom descriptions. For instance, Howell7 described such patients as characterized by episodic breathlessness that is poorly correlated with exercise, by more difficulties to breathe in than out, and by association with dizziness and paresthesia. Schwartzstein8 suggested the following set of symptoms characterizing such patients: inability to get a deep breath, palpitations, paresthesias, and anxiety. In a previous study,6 we explored the relationships among diseases causing dyspnea, the symptoms associated with an illness, CHEST / 133 / 4 / APRIL, 2008

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and descriptors used by a patient to describe the symptoms, and we observed that the language of dyspnea and associated symptoms in patients with MUD did provide important diagnostic clues. In the present study, we investigated whether descriptors of dyspnea and associated symptoms are differentially diagnostic to identify patients with MUD. For this purpose, a respiratory symptom checklist6 consisting of 61 spontaneously reported descriptors of dyspnea and associated symptoms was administered to a group of patients with MUD and another group with cardiopulmonary diseases. Symptom factors were derived by a principal component analysis on the wide range of descriptors. The separation of two patient groups in terms of symptom factors was achieved by a discriminant analysis. The obtained results allowed to address the following questions: (1) are descriptors of dyspnea in patients with MUD different from those with cardiopulmonary diseases, and (2) to what extent are they differentially related to individual diagnosis of MUD?

Materials and Methods Subjects After approval of the study by the ethical committee of medical research of Peking Union Medical College Hospital, two populations of patients were investigated. Informed consent was acquired from patients. Patients With MUD: A total of 96 patients with MUD were recruited from the pulmonary clinic of Peking Union Medical College Hospital. The diagnosis of MUD was based on the presence of marked dyspnea and the absence of objective evidence for an organic disease that could explain the symptom.6,11 Organic diseases as a cause of dyspnea were excluded on the basis of a dyspnea workup including medical history and physical examination; hemoglobin determination; chest radiograph and/or CT; pulmonary function tests; arterial blood gases; ECG; and echocardiog*From the Department of Pneumology (Drs. Han, Zhu, and Li), Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, China; Heart Failure Intensive Care Unit (Drs. Zhang and Cheng), Fu Wai Hospital and Cardiovascular Institute, Beijing, China; Department of Psychology (Dr. Van Den Bergh), University of Leuven, Leuven, Belgium; and Department of Pneumology (Dr. Van de Woestijne), U Z Gasthuisberg. Leuven, Belgium. This study was supported by grant BIL01/05 of the Bilateral Scientific and Technological Cooperation between Belgium and China, and was performed in Peking Union Medical College Hospital. None of the authors have declared any conflicts of interest to disclose. Manuscript received August 29, 2007; revision accepted December 19, 2007. Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (www.chestjournal. org/misc/reprints.shtml). Correspondence to: Jiangna Han, MD, FCCP, Department of Pneumology, Peking Union Medical College Hospital, Shuai Fu Yuan No. 1, Beijing, 100730, China; e-mail: [email protected] DOI: 10.1378/chest.07-2179 962

raphy. In addition, methacholine challenge testing, exercise testing, lung scans, thyroid function tests, and coronary angiography were performed when indicated. Patients With Dyspnea Due to Cardiopulmonary Diseases: A total of 195 patients presenting with dyspnea due to a variety of cardiopulmonary diseases were recruited from Peking Union Medical College Hospital and Fu Wai Hospital and Cardiovascular Institute. Among the cardiopulmonary diseases were congestive heart failure (n ⫽ 65), asthma (n ⫽ 66), interstitial lung diseases (n ⫽ 17), pulmonary embolism (n ⫽ 10), COPD (n ⫽ 7), pulmonary hypertension (n ⫽ 6), pleural effusion (n ⫽ 5), lung cancer (n ⫽ 4), bronchiectasis (n ⫽ 3), pneumothorax (n ⫽ 3), alveolar proteinosis (n ⫽ 3), upper airway obstruction (n ⫽ 2), bronchial tuberculosis (n ⫽ 1), pulmonary veno-occlusive disease (n ⫽ 1), middle lobe syndrome (n ⫽ 1), and pulmonary sequestration (n ⫽ 1). Methods A respiratory symptom checklist6 consisting of 61 spontaneously reported descriptors of dyspnea and associated symptoms was administered to patients, who filled out the checklist while at consultation or during hospitalization. Family members were not present, and patients were left alone and given as much time as they needed. Most subjects needed from 10 to 15 min. They rated the frequency with which he/she experienced each descriptor during the past month by marking the appropriate point on a 5-point scale (0 ⫽ never occurring, 1 ⫽ rare, 2 ⫽ sometimes, 3 ⫽ often, 4 ⫽ very often). When assistance was requested, the investigators took care not to suggest any answers. After completion of the checklist, the subjects were asked to check for any missing item and to complete it. Statistical Analysis A principal component analysis with orthogonal varimax rotation was used to classify the wide range of descriptors into a number of clinically meaningful and interpretable symptom factors. Because in our previous study descriptors of dizziness, shaking or trembling, cold hands or feet, flushing to the head, sudden hot or cold, and chest pain did not reach a minimal loading of 0.40 for item classification,6 they were not introduced into the data analysis. The principal component analysis on the remaining 55 descriptors yielded 12 consecutive and uncorrelated factors based on the minimal eigenvalue criterion (⬎ 1), explaining 64.4% of the total variance. After varimax rotation, the pattern of loadings of the descriptors on each factor was obtained (Appendix). However, the minimal eigenvalue criterion sometimes retains too many factors. An additional criterion was used: the extent to which a solution is interpretable. Ten factors that made the best “sense” were retained. Factor scores were generated per subject. These factor scores were used in a discriminant analysis to investigate which combination of the symptom factors separated patients with MUD from

Table 1—Characteristics of Two Groups of Patients Characteristics Patients, No. Male Female Age, yr*

MUD

Cardiopulmonary Diseases

96 37 59 34.7 ⫾ 10.9†

195 95 100 49.2 ⫾ 14.0

*Mean ⫾ SD. †Significant difference with respect to patients with cardiopulmonary diseases (p ⬍ 0.0001). Original Research

those with cardiopulmonary diseases. A backward selection procedure was used to eliminate the factors that did not contribute significantly to the discriminant function. The discriminant analysis allowed to classify each subject as a patient with MUD or with cardiopulmonary disease. Finally, the sensitivity and specificity were computed. All analyses were performed using statistical software (SAS version 8.02; SAS Institute; Cary, NC).

Results Characteristics of Patients Table 1 shows the characteristics of two groups of patients. As can be seen, patients with MUD were younger than patients with cardiopulmonary diseases. There were more female patients in the group of MUD, although the difference did not reach a statistically significant level (61% vs 51%, p ⫽ 0.10). Symptom Factors Ten factors were retained and defined in order of importance according to the proportion of eigenvalues: factor 1 (urge to breathe) consisted of 11 descriptors: a need to take a deep inspiration, my breath does not go in all the way, attempt to breathe in with much effort, sighing, hunger for more air, shortness of breath, I cannot breathe in, inability to breathe in deeply enough, breathing with difficulty (with effort), my breathing needs conscious help, and

I cannot breathe enough; factor 2 (depth and frequency of breathing): breathing more, breathing fast, rapid respiration, exhaling more, gasping, and desperate for breath to come; factor 3 (anxiety): nervousness, a restless heart or restless, irritated, fear, experiencing the agony of dying, and fatigue; factor 4 (affective aspect of dyspnea): compressed chest, oppressive chest, being suffocated, blocked chi in the chest, chest tightness, and tight or lump in throat; factor 5 (difficulty breathing and phase of respiration): I cannot breathe out, my breath does not go out all the way, inability to breathe in and out, and difficult to breathe out; factor 6 (wheezing): whistling in the throat, whistling in exhalation, and whistling while breathing; factor 7 (tingling): tingling face, tingling head or body, tingling fingers or arms, and tingling legs or feet; factor 8 (cough and sputum): expectoration, cough, mucous congestion, and hemoptysis; factor 9 (out of control): out of control or getting crazy, feeling faint, blocked chi in the throat, and stiff fingers, arms or legs; and factor 10 (palpitation): pounding heart, palpitation, I cannot walk on level or up the stairs, and I cannot lie down. Discriminative Function of the Symptom Factors In a discriminant analysis, the selected factors separating patients with MUD from those with cardiopulmonary diseases were the following: urge to

70 cardiopulmonary diseases

60

medically unexplained dyspnea

50

FREQUENCY

40 30 20 10 0 -3.9 -3.3 -2.7 -2.1 -1.5 -0.9 -0.3 0.3 0.9 1.5 2.1 2.7 3.3 3.9 4.5 DISCRIMINANT SCORES Figure 1. Frequency distribution of discriminant scores in two groups of patients. Note that when a limit set at 0.3, 14 patients with MUD (15%) and 24 patients with cardiopulmonary diseases (12%) were misclassified. www.chestjournal.org

CHEST / 133 / 4 / APRIL, 2008

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breathe, wheezing, affective aspect of dyspnea, anxiety, tingling, cough and sputum, and palpitation (R2 ⫽ 0.45, p ⬍ 0.0001). The coefficients of the factors urge to breathe, affective aspect of dyspnea, anxiety, and tingling were positive, meaning that the presence of these factors favored the diagnosis of MUD. Conversely, the factors wheezing, cough and sputum, and palpitation had negative coefficients, and their presence indicated the diagnosis of cardiopulmonary diseases. The discriminant analysis allowed to calculate a score for each subject. When a limit set at 0.3, the sensitivity for the diagnosis of MUD was 85% and the specificity 88% (Fig 1). Discussion In the present study, a respiratory symptom checklist consisting in 61 spontaneously reported descriptors of dyspnea and associated symptoms and scored on a 5-point scale of frequency of occurrence was administered to 96 patients with MUD and to 195 patients with dyspnea due to cardiopulmonary diseases. A principal component analysis on the wide

range of descriptors yielded 10 symptom factors. Five factors grouped different attributes of dyspnea: urge to breathe, depth and frequency of breathing, difficulty breathing and phase of respiration, wheezing, and affective aspect of dyspnea. The other five factors grouped symptoms of anxiety, tingling, cough and sputum, palpitation, and out of control. A discriminant analysis allowed to separate two patient groups (R2 ⫽ 0.45, p ⬍ 0.0001). The presence of urge to breathe, affective aspect of dyspnea, anxiety, and tingling pointed to the diagnosis of MUD, whereas the reporting of wheezing, cough and sputum, and palpitation indicated cardiopulmonary diseases. The sensitivity was 85%, and specificity was 88%. These findings complement nearly 2 decades of effort to characterize the qualitative aspects of dyspnea and to relate the language of dyspnea to specific diagnosis of an illness. Sensory Dimension of Breathlessness In 1989, Simon et al12 initially developed a list of 19 phrases describing breathing discomfort. The investigators administered the descriptors to normal

Table 2—Comparison Between Descriptors in Attributes of Dyspnea Dimensions of Dyspnea Sensory dimension Urge to breathe

Depth and frequency of breathing

Descriptors in Study by Harver et al15 I feel out of breath I feel a hunger for air My breathing requires effort My breathing requires work I cannot get enough air in

I feel that I am breathing more I feel that my breathing is rapid My breathing is shallow

Difficulty breathing and phase of respiration

My breath does not go out all the way

My breath does not go in all the way Wheezing

Affective dimension

964

Descriptors in the Present Study Shortness of breath Hunger for more air Breathing with difficulty (with effort) Attempt to breathe in with much effort Sighing Inability to breathe in deeply enough A need to take a deep inspiration I cannot breathe enough My breath does not go in all the way I cannot breathe in My breathing needs conscious help Breathing more Exhaling more Breathing fast Rapid respiration Gasping Desperate for breath to come My breath does not go out all the way Difficult to breathe out I cannot breathe out Inability to breathe in and out Whistling in throat Whistling in exhalation Whistling while breathing Compressed chest Oppressive chest Being suffocated Blocked chi in the chest Chest tightness Tight or lump throat

Original Research

subjects and found that different stimuli that were used to induce breathlessness resulted in a different combination of descriptors. Subsequently, they extended the observations to patients with breathlessness due to a variety of cardiopulmonary diseases.13,14 As in the normal subjects, dyspnea of different disease states appeared to be characterized by different qualitative descriptors. Harver et al15 administered 15 descriptors to normal subjects and asked them to judge the dissimilarity between pairs of descriptors. By applying cluster analysis and multidimensional scaling algorithms to dissimilarity ratings, the investigators were able to classify these 15 descriptors into three attributes of breathing discomfort: perceived need or urge to breathe, depth and frequency of breathing, and difficulty breathing and phase of respiration. Despite the differences in methodology, three qualitative aspects of dyspnea proposed by Harver et al15 were confirmed in the present study of patients with dyspnea. Comparison between descriptors in these attributes of breathing discomfort showed considerable overlap with factor 1 (urge to breathe, characterized by the act of taking a deep breath to relieve the urge to breathe), factor 2 (depth and frequency of breathing, characterized by an increase of volume and breathing frequency), and factor 5 (difficulty breathing and phase of respiration, characterized by a phasic component related to difficult breathing) [Table 2]. However, as in our previous study,6 two other factors of breathing discomfort (factor 4 and factor 6) emerged in the present study. Factor 6 grouped the descriptors of whistling during respiration (whistling in the throat, whistling in exhalation, and whistling while breathing). These descriptors match perfectly with the classical term of wheezing.16,17 Obviously, these four attributes of breathlessness are fundamentally linked to the physiology of breathing as important sources of sensory information. Any abnormalities during the act of breathing (ie, increased respiratory drive, inappropriateness in volume, frequency, and phase of respiration, or airway obstruction) may subsequently lead to distinct and separable sensations of breathlessness. Affective Dimension of Breathlessness Dyspnea, like pain, has a multidimensional nature containing both sensory and affective components. The affective component has been regarded as a nonspecific unpleasant or distressing experience of dyspnea.18 Studies19,20 have shown that normal subjects as well as patients with asthma are capable of distinguishing between the sensory dyspnea and the distressing experience. However, the question that remains is how patients verbalize their experience of affective dyspnea. Of interest, factor 4 of the present www.chestjournal.org

study grouped both descriptors that are usually associated with anxiety and somatoform disorders21 and descriptors that are ordinarily associated with asthma (eg, chest tightness).14 This factor has been shown to be specifically linked to two disparate patient groups of MUD and asthma.6 It may make sense from the point of view that asthmatic patients are seen as existing on a continuum in which some of the patients report symptoms that are disproportionately severe in relation to the extent of lung function impairment.22 In this regard, this factor appears to be more related to affectivity than to the physiology of breathing. Therefore, phrases in factor 4 may be considered as verbal descriptors typical of affective dyspnea in patients. Taken together, our study suggested two dimensions of the sensory and the affective dyspnea with a total number of five attributes of breathing discomfort. Cultural Influences on the Language of Dyspnea In the present study, the five attributes of breathing discomfort were obtained from the study of Chinese people. One may question to what extent Chinese culture influences the language of dyspnea. Compared to the descriptors developed in individuals from the United States, there were considerable overlap in the descriptions of breathing discomfort related to urge to breathe, depth and frequency of breathing, difficulty breathing and phase of respiration, and wheezing (Table 2). It is apparent that “east meets west” more comfortably regarding the sensory dimension of breathlessness. As for the affective dimension of breathlessness, descriptors specific for Chinese culture emerged in

Table 3—Diagnosing MUD Medical history Presence of following symptoms should increase the suspicion of MUD A need to take a deep inspiration Oppressive chest or compressed chest Anxiety: nervous, restless Tingling in fingers, feet, face or head Absence of following symptoms Wheezing: whistling sounds while breathing Cough and expectoration Palpitation Physical examination Normal examination of cardiopulmonary systems Normal findings of following laboratory tests ECG Chest radiograph Spirometry Arterial blood gas analysis* *The analysis of arterial blood gases could show either normal results or respiratory alkalosis. CHEST / 133 / 4 / APRIL, 2008

965

factor 4, for example, blocked chi in the chest, which means the circulation of living energy along specific channels is blocked in the pathway to chest. According to some authors,23,24 Western people use more intrapsychic conceptualizations of emotions, whereas Chinese people would prefer to use phases associated with anatomy to describe their affective experiences. In view of the tendency of Chinese people to express emotions in terms of bodily sensations, affective dyspnea appears more likely to be influenced by cultural differences and emotional meanings. Diagnostic Value of Symptom Factors To what extent is the language of dyspnea differentially related to individual diagnosis of MUD? The language of dyspnea specific for MUD appeared to be urge to breathe and affective aspect of dyspnea. This was not unexpected in view of excessive respiratory drive leading to hyperventilation4 and predominant anxiety2,9,10,11 in those patients. Contrasting to MUD, descriptors of cardiopulmonary dyspnea were mainly related to wheezing. However,

other symptom factors also contributed importantly to the differentiation. Anxiety and tingling appeared to be unique for patients with MUD, whereas cough and sputum and palpitation were linked to the diagnosis of cardiopulmonary diseases. This would mean that if a patient reports cough and expectoration, a diagnosis of MUD is very unlikely. Use of the descriptors of dyspnea and associated symptoms achieved correct separation in 85% patients with MUD and 88% patients with cardiopulmonary diseases. As physicians, we were taught early in the beginning of our careers that medical history provides most important diagnostic information. This principle holds true in the diagnosis of MUD if physicians ask right questions in medical interview. Symptoms specific for diagnosis and differential diagnosis of MUD are listed in Table 3. It should be realized that this descriptor model was derived from a cross-sectional study. A prospective study will be required to further test the validity and predictive values of the descriptor model in another cohort of patients.

Appendix

Pattern of Loadings for 55 Descriptors on Each Factor Derived From Varimax Rotation in 291 Patients* Descriptors Tingling fingers or arms Tingling legs or feet Tingling face Tingling head or body Attempt to breathe in with much effort Being suffocated Compressed chest Blurred vision Nervousness Shortness of breath Experiencing the agony of dying Blocked chi in the chest Tight or lump throat Blackness before eyes Oppressive chest Palpitation Fear Stiff fingers, arms, or legs Feeling faint Fatigue Irritated A restless heart, restless Sighing My breathing needs conscious help Blocked chi in the throat

966

F1

F2

F3

F4

0.15 0.05 0.12 0.14 0.63†

0.01 0.01 0.04 0.08 0.06

0.16 0.05 0.02 0.19 0.14

0.14 0.23 0.04 0.14 0.08

0.36 0.21 0.10 0.08 0.13 ⫺ 0.12 0.14 0.05 0.58† 0.24 0.17 ⫺ 0.01

0.00 0.17 0.18 0.77† 0.09 0.54†

0.23 0.16 0.30 ⫺ 0.04 0.05 0.31 0.19 0.19 0.09 0.16 0.21 ⫺ 0.05 0.13 0.08 ⫺ 0.06 0.20 0.11 0.31 0.16 0.12 0.18 0.07 0.59† 0.12 0.49† 0.14

0.23 0.28 0.24 0.24 0.41 0.68† 0.14 0.01 0.42† 0.74† 0.76† 0.30 0.27

0.25

0.02

0.21

F5

F6

F8

F9

F10

F11

F12

0.70† 0.69† 0.74† 0.71† 0.11

0.02 0.09 0.06 ⫺ 0.09 ⫺ 0.06 0.13 ⫺ 0.07 0.02 ⫺ 0.05 0.27

⫺ 0.06 ⫺ 0.03 0.09 0.03 0.13

0.18 0.32 ⫺ 0.20 ⫺ 0.03 ⫺ 0.10

0.67† 0.14 0.02 0.77† 0.08 0.02 0.08 0.06 0.11 0.16 0.13 ⫺ 0.05 0.39 ⫺ 0.00 0.12 0.16 0.14 0.10

0.05 0.16 0.08 0.12 0.07 0.22

⫺ 0.03 ⫺ 0.01 0.03 0.06 0.16 0.11 ⫺ 0.03 0.09 ⫺ 0.04 ⫺ 0.13 ⫺ 0.06 0.19

0.04 0.13 0.14 ⫺ 0.04 0.11 0.21

⫺ 0.03 0.05 0.67† ⫺ 0.01 0.11 ⫺ 0.06

0.14 0.04 0.00 0.06 0.10 0.41

0.59† 0.22 0.11 0.41† 0.21 0.28 0.04 0.12 ⫺ 0.14 0.72† 0.07 ⫺ 0.06 0.41 0.01 ⫺ 0.06 0.04 0.08 0.07 0.06 0.14 0.08 ⫺ 0.01 0.10 0.03 0.36 ⫺ 0.14 ⫺ 0.04 0.24 0.12 ⫺ 0.02 0.14 0.10 ⫺ 0.04 0.24 0.03 ⫺ 0.13 0.13 0.23 ⫺ 0.15

0.18 0.11 0.22 0.14 0.14 0.18 0.35 0.08 0.09 0.08 0.03 0.21 0.16

⫺ 0.05 0.22 0.20 0.31 0.14 0.19 0.02 0.01 0.04 0.11 ⫺ 0.06 0.29 0.06 0.43† ⫺ 0.22 0.61† ⫺ 0.08 ⫺ 0.11 0.07 ⫺ 0.00 0.13 0.09 0.03 ⫺ 0.02 0.03 0.18

⫺ 0.27 0.09 ⫺ 0.05 0.10 0.07 0.50† 0.11 0.09 0.55† 0.08 0.21 ⫺ 0.04 0.16 0.09 0.06 0.33 0.16 0.26 ⫺ 0.06 0.18 0.05 0.14 ⫺ 0.10 0.20 ⫺ 0.18 0.03

0.01 ⫺ 0.01 0.08 0.05 ⫺ 0.01 0.08 ⫺ 0.21 0.04 0.11 0.01 0.00 ⫺ 0.15 0.12

0.01

⫺ 0.00

0.35

⫺ 0.07 0.05 ⫺ 0.06 0.06 0.02 ⫺ 0.09 0.13 ⫺ 0.01 ⫺ 0.01 0.10

F7

0.15

0.26

0.47† ⫺ 0.04

0.05 0.00 0.14 ⫺ 0.06 ⫺ 0.03

0.06 0.11 (Continued)

Original Research

Continued Descriptors

F1

Inability to breathe in deeply enough Out of control or getting crazy Pounding heart Gasping Chest tightness Whistling while breathing Whistling in throat Difficult to breathe out My breath does not go in all the way Whistling in exhalation I cannot breathe enough Desperate for breath to come My breath does not go out all the way Breathing more Breathing fast Breathing with difficulty (with effort) I cannot breathe in Inability to breathe in and out Exhaling more Hunger for more air A need to take a deep inspiration Rapid respiration I cannot breathe out Coughing Mucous congestion Expectoration Hemoptysis My breathing stopped I cannot walk on level or up the stairs I cannot lie down Variance explained by each factor, %

F2

F3

F4

F5

F6

F7

F8

F9

0.52†

0.14

0.21

0.33

0.25 ⫺ 0.09

0.18

0.05

0.06

0.10

0.06

0.25

0.06

0.04 ⫺ 0.22

0.02

0.14

0.61†

0.11 0.15 0.21 0.27 ⫺ 0.03 ⫺ 0.05 0.09 0.21 0.20 0.47† ⫺ 0.14 ⫺ 0.06 0.13 0.34 ⫺ 0.08 0.18 0.25 ⫺ 0.08 0.17 0.56† 0.30 0.05 0.23 0.13 0.01 0.23 ⫺ 0.01 ⫺ 0.03 0.15 0.76† 0.01 0.27 0.00 0.15 0.00 0.08 0.10 0.78† ⫺ 0.03 0.19 0.34 0.37 0.23 0.29 0.45† 0.08 ⫺ 0.03 ⫺ 0.06 0.64† 0.18 0.16 0.14 0.39 0.11 0.07 ⫺ 0.04

0.14

0.06

⫺ 0.08

0.06

0.17 0.06 0.07

0.08 0.04 ⫺ 0.04

⫺ 0.01 0.16 0.15

⫺ 0.01 ⫺ 0.03 0.02 ⫺ 0.02 ⫺ 0.07 0.02

0.00 ⫺ 0.06 0.04 0.08 0.07 0.09 0.02 0.01 0.21 0.04

⫺ 0.00 0.23 0.09 ⫺ 0.03 0.11

0.16 ⫺ 0.12 0.02 0.10 0.00

0.02 0.16 0.08 0.44 ⫺ 0.05 ⫺ 0.11 0.06 0.22 0.12 ⫺ 0.09

0.23 0.06 0.74† 0.13 0.03 0.25 0.08 0.21 0.07 0.28 0.04 0.14 0.06 ⫺ 0.05 0.23 0.16

0.07 0.08 0.03 0.15 ⫺ 0.06 0.71† ⫺ 0.07 0.63† 0.06 0.79† ⫺ 0.03 0.53† 0.05 0.08 ⫺ 0.05 ⫺ 0.01

0.16 0.13 ⫺ 0.10 0.21 ⫺ 0.01 ⫺ 0.02 ⫺ 0.01 0.01

0.06 0.14 0.14 ⫺ 0.16 0.07 0.21 0.07 0.58†

0.13 ⫺ 0.01 ⫺ 0.01 0.02 0.01 ⫺ 0.06 0.16 0.26 ⫺ 0.01 ⫺ 0.02 0.40 0.03 0.05 0.83† 0.33 0.22

0.44 8.9

⫺ 0.01 7.7

⫺ 0.07 5.5

0.44† 5.5

0.76† 0.75† 0.46

0.04 0.07 0.11

0.07 ⫺ 0.01 0.11 0.22 0.10 0.35

0.52† 0.22 0.31 0.59† 0.76†

0.33 0.06 0.64† 0.34 0.10

0.10 0.21 0.03 0.14 0.09

0.04 0.49 0.03 0.08 0.50† 0.18 0.09 ⫺ 0.05 0.28 0.24 0.12 0.06 0.13 0.09 ⫺ 0.02

0.02 11.1

0.06

⫺ 0.02 0.13 0.08 ⫺ 0.01

0.19 0.14 0.51†

0.13 11.1

⫺ 0.09

0.05 ⫺ 0.08 0.01 0.13

0.02 0.23 0.18 0.23

0.16 11.6

F12

0.59† 0.35 0.15 0.06 0.06 ⫺ 0.04 0.03

0.23 ⫺ 0.06 0.43 0.10 0.43† 0.15 0.15 0.14

0.00 14.4

F11

0.26 0.01 0.11 ⫺ 0.05 ⫺ 0.03 0.01 0.07

0.04 0.49† 0.34 0.32

0.13 0.67† 0.08 0.19 0.15 0.16 0.09 0.17 ⫺ 0.13 0.27 0.02 0.01 0.13 0.04 0.12 ⫺ 0.01 ⫺ 0.05 0.11 0.01 ⫺ 0.01 0.04 0.02 ⫺ 0.05 0.12 0.09 ⫺ 0.07 0.10 0.12 0.02 0.22 ⫺ 0.11 ⫺ 0.03

F10

0.09 0.25 0.36 0.69†

0.78† 0.12 0.14 0.14 0.26 0.09 0.01

0.16 8.0

0.03 0.24 0.03 ⫺ 0.08 0.02 0.08 0.02 0.00 0.05 0.05 ⫺ 0.06

0.14 6.8

0.06 0.03 ⫺ 0.10 0.02 ⫺ 0.07 ⫺ 0.02 0.02 0.02 0.03 ⫺ 0.02 0.00 0.24 ⫺ 0.01 0.16 0.06 0.02 0.21 0.12

0.04 0.28 0.04 0.03

0.14 ⫺ 0.12 4.8 4.7

*F1 ⫽ factor 1 (urge to breathe); F2 ⫽ factor 2 (depth and frequency of breathing); F3 ⫽ factor 3 (anxiety); F4 ⫽ factor 4 (affective aspect of dyspnea); F5 ⫽ factor 5 (difficulty breathing and phase of respiration); F6 ⫽ factor 6 (wheezing); F7 ⫽ factor 7 (tingling); F8 ⫽ factor 8 (cough and sputum); F9 ⫽ factor 9 (out of control); F10 ⫽ factor 10 (palpitation). †Highest correlation.

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