- Email: [email protected]
Cardiovascular responses to the change from the left lateral to the upright position in pregnant hypertensives
International Journal of Gynecology and Obstetrics 84 (2004) 208–213
Article
Cardiovascular responses to the change from the left lateral to the upright position in pregnant hypertensives R.A. Dyera,*, J. Anthonyb, Q. Ledeboerb, M.F. Jamesa a Department of Anaesthesia, University of Cape Town and New Groote Schuur Hospital, Cape Town, South Africa Department of Obstetrics and Gynaecology, University of Cape Town and New Groote Schuur Hospital, Cape Town, South Africa
b
Received 30 April 2003; received in revised form 24 July 2003; accepted 30 July 2003
Abstract Objective: To evaluate by non-invasive means, the autonomically mediated changes in heart rate and blood pressure in response to postural change in pregnancy. Method: Ninety-one patients were studied, of whom 17 were nonpregnant controls, 21 were normotensive parturients, 22 had non-proteinuric hypertension, and 31 were pre-eclamptics. In all patients the heart rate and blood pressure response to the change from the left lateral to the erect position was measured non-invasively, during the third trimester in the pregnant groups. Results: The change from the left lateral to the erect position induced significantly greater mean changes (increases) in systolic blood pressure in the normotensive pregnant (PC) women than all other groups (P-0.05). Pre-eclamptic patients (PE) exhibited significantly less of an increase in systolic blood pressure than the non-proteinuric hypertensive (H) group. Both the H and PC groups showed significantly greater increases in diastolic pressure than the non-pregnant (NP) group. PE patients had a significantly smaller increase in diastolic pressure than the H group. There were no significant differences between heart rate changes when comparing the PC, NP and H groups. The PE group exhibited a significantly greater increase in heart rate on adopting the erect position than all other groups. Conclusions: Preeclamptics exhibit smaller changes in blood pressure than normotensive pregnant patients and non-proteinuric hypertensives on standing, while producing an exaggerated heart rate response, indicating altered autonomic compensatory mechanisms in these patients. 䊚 2003 International Federation of Gynecology and Obstetrics. Published by Elsevier Science Ireland Ltd. All rights reserved. Keywords: Pre-eclampsia; Autonomic nervous system
1. Introduction Normal pregnancy is associated with well*Corresponding author. Tel.: q27-2127-404-5003; fax: q 27-2127-447-5206. E-mail address: [email protected] (R.A. Dyer).
described cardiovascular physiological changes, namely increased blood volume, increased heart rate, decreased systemic vascular resistance, increased cardiac output, and the development of aortocaval occlusion w1x. In addition, it is now well established that pregnancy is associated with altered autonomic cardiovascular responses, and
0020-7292/04/$30.00 䊚 2003 International Federation of Gynecology and Obstetrics. Published by Elsevier Science Ireland Ltd. All rights reserved. doi:10.1016/S0020-7292(03)00343-6
R.A. Dyer et al. / International Journal of Gynecology and Obstetrics 84 (2004) 208–213
that pre-eclamptic patients exhibit different cardiovascular responses from those of healthy parturients w2–7x. The aim of this study was to evaluate autonomically-mediated changes in blood pressure during pregnancy by non-invasive means in nonpregnant controls, healthy pregnant women, pregnant women with chronic hypertension and pre-eclamptic parturients. 2. Patients and methods In order to characterize the autonomic responses in our patient population, the cardiovascular response to a change in position from left lateral to erect was studied in four groups of patients: 1. proteinuric hypertensive group (PE), including: a pre-eclampsia; b unclassified proteinuric hypertension; 2. hypertensive group (H), including: a chronic hypertension; b non-proteinuric gestational hypertension; c. unclassified non-proteinuric hypertension; 3. normotensive pregnant control group (PC); and 4. non-pregnant group (NP). The pre-eclamptic group (PE) contained women with no previous history of hypertension, cardiovascular or renal disease before pregnancy, who had developed persistent diastolic hypertension in excess of 90 mmHg after the 20th week of gestation, together with proteinuria, defined as 2q dipstick proteinuria on more than one occasion, or 24-h quantification in excess of 300 mg. Also included in this group were women with unclassified proteinuric hypertension. The hypertensive group (H) consisted of women with chronic hypertension, women who developed non-proteinuric hypertension during pregnancy, and those who exhibited unclassified non-proteinuric hypertension. The normotensive group (PC) contained parturients with a blood pressure below 140y90 and no history of hypertension. The non-pregnant group (NP) consisted of female members of the Groote Schuur Hospital staff in the child-bearing age-group. Demographic data on all groups, and specific details concerning the severity of hypertension and pharmacological therapy in the GPH and H groups, appear in Table 1.
209
Informed consent was obtained from each patient after approval by the University of Cape Town Ethics Committee. Using an Omron oscillometric automatic digital blood pressure monitor (Model HEM-705CP, heart rate reading accuracy "5%, blood pressure reading accuracy "3 mmHg, or "2%), heart rate (HR) and systolic (SBP) and diastolic blood pressures (DBP) were first measured with the cuff held at the level of the right atrium and with the patient in the left lateral position. Thereafter, the heart rate and blood pressure were measured 1 min after standing up. Each test was performed five times to obtain a mean reading. Between each measurement the subject had 10 min of bed rest in the lateral position. 2.1. Statistics Statistical analysis was carried out using ANOVA for continuous normally distributed data and appropriate non-parametric tests for data that was not normally distributed. Analysis of variance for repeated measures was used to evaluate the possibility of significant time-based effects within groups. As none were found, all five measures for each patient were grouped and averaged. 3. Results Demographic data, drug therapy, and baseline cardiovascular data are shown in Table 1. The SBP and DBP at rest in the left lateral position were significantly higher in both PE and H women, compared with non-pregnant and normal pregnant women. The NP group had significantly lower resting heart rates than all other groups. The PC group had a significantly higher resting HR than the PE group. There were no significant differences between consecutive measures of SBP, DBP or HR in any of the groups, i.e. there was no time-based effect. The mean changes in each group in SBP, DBP and HR after a change from the left lateral to the erect position, are shown in Figs. 1–3. (A positive change in blood pressure or HR represents an increase in either parameter on adopting the erect
210
Non-pregnant controls (NP) Number Mean age (years) (S.D.) Height (cm) (S.D.) Weight (kg) (S.D.) Parity (range) Gravidity (range) Gest. age (weeks) Aldomet CCB CCBqAldomet Atenololqdiuretic SBP L (S.D.) DBP L (S.D.) PR L (S.D.)
17 30.6 (8.4) 164.1 (6.9) 58.6 (8.7) 0 (0–3) 0 (0–3) NyA Nil Nil Nil Nil 111.0 (8.8) 68.2 (7.4) 70.3 (10.7)
P
-0.05 NP)PC, PE, H -0.05 NP-PE, H
-0.05 NP-PC, PE, H
Normotensive (PC) 21 26.3 (5.7) 156.3 (6.7) 66.7 (17.5) 1 (0-3) 2 (1-6) 37.6 (3.0) Nil Nil Nil Nil 108 (13.5) 63.5 (10.8) 82.3 (14.1)
P
-0.05 PC)PE
Proteinuric hypertension (PE) 31 26.8 (6.6) 156.9 (6.7) 73.4 (19.5) 1 (0–4) 2 (1–5) 33.5 (3.7) 16 6 3 Nil 139.8 (20.3) 86.6 (17.3) 76.7 (12.9)
P
-0.05 PE)NP, PC -0.05 PE)NP, PC
Hypertension (H) 22 29.8 (6.8) 159.4 (6.4) 80.0 (20.3) 1 (0-4) 2 (1-5) 36.5 (3.1) 5 2 2 1 135.1 (19.4) 82.4 (13.8) 79.7 (14.9)
P
-0.05 H)PC, NP
-0.05 H)NP, PC -0.05 H)NP, PC
Statistical significance if P-0.05; S.D., standard deviation; Gest. age, gestational age; CCB, calcium channel blocker; SBP L, systolic blood pressure in the left lateral position; DBP L, diastolic blood pressure in the left lateral position; PR L, pulse rate in the left lateral position.
R.A. Dyer et al. / International Journal of Gynecology and Obstetrics 84 (2004) 208–213
Table 1 Demographic data, drug therapy, and baseline cardiovascular data
R.A. Dyer et al. / International Journal of Gynecology and Obstetrics 84 (2004) 208–213
q
Fig. 1. SBP, systolic blood pressure. *PC significantly greater than all other groups.
position.) The results may be summarized as follows: ● The PC group exhibited significantly greater mean changes (increases) in SBP than the NP, PE and H groups, when the erect position was adopted. The PE group exhibited significantly less of an increase in SBP than the H group. ● Both the H and the PC group showed significantly greater increases in DBP than the NP group. The PE patients showed a significantly smaller increase in DBP than the H group and
211
H significantly greater than PE.
a trend towards a smaller diastolic change than that seen in the PC group. ● There were no significant differences between HR changes when comparing the PC, NP and H groups. The PE group exhibited a significantly greater mean increase in HR on adopting the erect position than all other groups. 4. Discussion Early studies involving cardiovascular autonomic changes in pregnancy examined the effects of
Fig. 2. DBP, diastolic blood pressure. *H and PC significantly greater than NP.
q
H significantly greater than PE.
212
R.A. Dyer et al. / International Journal of Gynecology and Obstetrics 84 (2004) 208–213
Fig. 3. PR, pulse rate. *PE significantly greater than all other groups.
changes in position, employing simple tests such as changes in pulse and blood pressure in response to a change from the supine to the erect position, and to the Valsalva maneuver, as well as to changes in respiratory pattern w2–5x. Only one study has employed invasive monitoring in the form of pulmonary artery catheterization to demonstrate the response to an orthostatic maneuver in normal pregnant patients w1x. Measurements were made during the third trimester, and repeated 6 weeks postpartum in the same patients. Both during pregnancy and 6 weeks postpartum, cardiac output decreased during orthostasis. It was concluded that during pregnancy the increased blood volume resulted in less marked decreases in cardiac output during the orthostatic maneuver than postpartum. In the postpartum period, there was a greater rise in peripheral resistance during the maneuver than during pregnancy, which contributed to the maintenance of blood pressure that did not change significantly during orthostasis. The present study, involving four groups of patients (proteinuric hypertensives, non-proteinuric hypertensives, a normotensive pregnant control group, and a nonpregnant group) (Table 1), did not reflect the same changes in blood pressure as those described by Clark. The change from left lateral to the erect position induced significantly greater mean changes (and an increase) in the systolic and DBP in
the PC group than in the NP group (Figs. 1 and 2). As in Clark’s study, the HR increased in these two groups, but there were no significant between group differences (Fig. 3). There are some obvious differences between Clark’s study and our findings. All groups in our study showed a rise in DBP and a rise in HR that presumably reflects a sympathetic response and rising peripheral vascular resistance (Fig. 2). This is consistent with Clark’s findings. The increase in SBP seen in our study differed from Clark’s findings and may reflect a more immediate hemodynamic response than those measured by Clark, who assessed his subjects 10 min after assuming a change in posture. The PE group in the current study exhibited greater increases in HR in response to an orthostatic maneuver than the NP and PC groups (Fig. 3). In addition, they did not exhibit the same rise in SBP as did the PC group. The exaggerated change in HR rate may suggest a greater sympathetic response than seen in the PC patients. The absence of any change in systolic pressure may reflect the decreased intravascular volume and the already raised systemic vascular resistance in these patients. There is considerable evidence for altered cardiovascular autonomic control in pre-eclampsia. In an evaluation of autonomic function in pre-eclamptics in the third trimester, HR responses to deep
R.A. Dyer et al. / International Journal of Gynecology and Obstetrics 84 (2004) 208–213
breathing and standing up were less marked in severe pre-eclamptics than in the control group w4x. This was interpreted as a relative inability to regulate HR and blood pressure in response to postural alterations. These data are at variance with our findings, although the authors of this study showed that in mild pre-eclamptics, cardiovascular reflexes were found to be normal and suggested that autonomic dysfunction is a condition that may evolve during the pathogenesis of severe disease. Another study demonstrated that pre-eclamptic women reached their maximal HR in a shorter period of time after adopting the erect position, but did not sustain a HR as high as normotensive pregnant patients w3x. Overall, our data are therefore not inconsistent with previous work, although the exaggerated tachycardia has not been previously described. Alternative explanations for the differences apparent between pre-eclamptic women and controls may be due to changes in baroreceptor function. Early studies have demonstrated abrupt and profound reductions in blood pressure in response to hydralazine in women with severe pre-eclampsia which was attributed to baroreceptor dysfunction by the authors w2x. More recent publications describe computerized spectral analysis methods for heart rate variability (HRV) estimation as a measure of sympathovagal balance w5–7x. In general, high frequency components of the HRV are evidence of vagal predominance (demonstrated by a marked HRV in response to deep breathing), while low frequency components suggest a predominance of sympathetic activity (reflecting blood pressure oscillations). Pre-eclamptics have been shown to be characterized by a significantly reduced high frequency peak compared with healthy pregnant patients, suggesting decreased vagal control of the heart w5x. A recent investigation employing frequency domain analysis of short-term, stationary R–R intervals suggested that pre-eclampsia may be associated with increased sympathetic and decreased parasympathetic control of the heart w6x. However, another study suggested that baroreflex gain, evaluated by cross-spectral
213
analysis of SBP and pulse interval, was found to be lower in pre-eclamptic women both compared with non-pregnant and healthy pregnant subjects w7x. These findings are consistent with our data with respect to HR changes, although baroreflex responses were not obviously impaired in the preeclamptic women included in the current study. The literature thus contains conflicting data regarding the autonomic changes that characterize pre-eclampsia. The reasons for these differences may lie in variations in methodology and differences in the severity of pre-eclampsia studied. Drug therapy may give rise to confounding effects. Overall, our data suggest that proteinuric hypertensives exhibit altered autonomic compensatory mechanisms from those of healthy parturients, with particular reference to the heart rate response to standing. References w1x Clark SL, Cotton DB, Pivarnik JM, Lee W, Hankins GDV, Benedetti TJ, et al. Position change and central hemodynamic profile during normal third-trimester pregnancy and post partum. Am J Obstet Gynecol 1991;164:883 –887. w2x Wasserstrum N, Kirshon B, Rossavik IK, Willis RS, Moise KJ, Cotton DB. Implications of sino-aortic baroreceptor reflex dysfunction in severe pre-eclampsia. Obstet Gynecol 1989;74:34 –38. w3x Wouters EJM, Jaspers WJM, Kurver PJ, de Jong PA. Autonomic heart-rate control in response to standing in toxaemic and normotensive primigravid pregnancies. Eur J Obstet Gynecol Reprod Biol 1984;16:309 –314. w4x Airaksinen KEJ, Kirkinen P, Takkunen JT. Autonomic dysfunction in severe pre-eclampsia. Eur J Obstet Gynecol Reprod Biol 1985;19:269 –276. w5x Eneroth-Grimfors E, Westgren M, Ericson M, IhrmanSandahl C, Lindblad LE. Autonomic cardiovascular control in normal and pre-eclamptic pregnancy. Acta Obstet Gynecol Scand 1994;73:680 –684. w6x Yang CCH, Chao T-C, Kuo TBJ, Yin C-SY, Chen HI. Pre-eclamptic pregnancy is associated with increased sympathetic and decreased parasympathetic control of heart rate. Am J Physiol Heart Circ Physiol 2000;278(4):H1269 –H1273. w7x Molino P, Veglio F, Genova GC, Melchio R, Benedetto C, Chiarolini L, et al. Baroreflex control of heart rate is impaired in pre-eclampsia. J Hum Hypertens 1999;13:179 –183.
Article
Cardiovascular responses to the change from the left lateral to the upright position in pregnant hypertensives R.A. Dyera,*, J. Anthonyb, Q. Ledeboerb, M.F. Jamesa a Department of Anaesthesia, University of Cape Town and New Groote Schuur Hospital, Cape Town, South Africa Department of Obstetrics and Gynaecology, University of Cape Town and New Groote Schuur Hospital, Cape Town, South Africa
b
Received 30 April 2003; received in revised form 24 July 2003; accepted 30 July 2003
Abstract Objective: To evaluate by non-invasive means, the autonomically mediated changes in heart rate and blood pressure in response to postural change in pregnancy. Method: Ninety-one patients were studied, of whom 17 were nonpregnant controls, 21 were normotensive parturients, 22 had non-proteinuric hypertension, and 31 were pre-eclamptics. In all patients the heart rate and blood pressure response to the change from the left lateral to the erect position was measured non-invasively, during the third trimester in the pregnant groups. Results: The change from the left lateral to the erect position induced significantly greater mean changes (increases) in systolic blood pressure in the normotensive pregnant (PC) women than all other groups (P-0.05). Pre-eclamptic patients (PE) exhibited significantly less of an increase in systolic blood pressure than the non-proteinuric hypertensive (H) group. Both the H and PC groups showed significantly greater increases in diastolic pressure than the non-pregnant (NP) group. PE patients had a significantly smaller increase in diastolic pressure than the H group. There were no significant differences between heart rate changes when comparing the PC, NP and H groups. The PE group exhibited a significantly greater increase in heart rate on adopting the erect position than all other groups. Conclusions: Preeclamptics exhibit smaller changes in blood pressure than normotensive pregnant patients and non-proteinuric hypertensives on standing, while producing an exaggerated heart rate response, indicating altered autonomic compensatory mechanisms in these patients. 䊚 2003 International Federation of Gynecology and Obstetrics. Published by Elsevier Science Ireland Ltd. All rights reserved. Keywords: Pre-eclampsia; Autonomic nervous system
1. Introduction Normal pregnancy is associated with well*Corresponding author. Tel.: q27-2127-404-5003; fax: q 27-2127-447-5206. E-mail address: [email protected] (R.A. Dyer).
described cardiovascular physiological changes, namely increased blood volume, increased heart rate, decreased systemic vascular resistance, increased cardiac output, and the development of aortocaval occlusion w1x. In addition, it is now well established that pregnancy is associated with altered autonomic cardiovascular responses, and
0020-7292/04/$30.00 䊚 2003 International Federation of Gynecology and Obstetrics. Published by Elsevier Science Ireland Ltd. All rights reserved. doi:10.1016/S0020-7292(03)00343-6
R.A. Dyer et al. / International Journal of Gynecology and Obstetrics 84 (2004) 208–213
that pre-eclamptic patients exhibit different cardiovascular responses from those of healthy parturients w2–7x. The aim of this study was to evaluate autonomically-mediated changes in blood pressure during pregnancy by non-invasive means in nonpregnant controls, healthy pregnant women, pregnant women with chronic hypertension and pre-eclamptic parturients. 2. Patients and methods In order to characterize the autonomic responses in our patient population, the cardiovascular response to a change in position from left lateral to erect was studied in four groups of patients: 1. proteinuric hypertensive group (PE), including: a pre-eclampsia; b unclassified proteinuric hypertension; 2. hypertensive group (H), including: a chronic hypertension; b non-proteinuric gestational hypertension; c. unclassified non-proteinuric hypertension; 3. normotensive pregnant control group (PC); and 4. non-pregnant group (NP). The pre-eclamptic group (PE) contained women with no previous history of hypertension, cardiovascular or renal disease before pregnancy, who had developed persistent diastolic hypertension in excess of 90 mmHg after the 20th week of gestation, together with proteinuria, defined as 2q dipstick proteinuria on more than one occasion, or 24-h quantification in excess of 300 mg. Also included in this group were women with unclassified proteinuric hypertension. The hypertensive group (H) consisted of women with chronic hypertension, women who developed non-proteinuric hypertension during pregnancy, and those who exhibited unclassified non-proteinuric hypertension. The normotensive group (PC) contained parturients with a blood pressure below 140y90 and no history of hypertension. The non-pregnant group (NP) consisted of female members of the Groote Schuur Hospital staff in the child-bearing age-group. Demographic data on all groups, and specific details concerning the severity of hypertension and pharmacological therapy in the GPH and H groups, appear in Table 1.
209
Informed consent was obtained from each patient after approval by the University of Cape Town Ethics Committee. Using an Omron oscillometric automatic digital blood pressure monitor (Model HEM-705CP, heart rate reading accuracy "5%, blood pressure reading accuracy "3 mmHg, or "2%), heart rate (HR) and systolic (SBP) and diastolic blood pressures (DBP) were first measured with the cuff held at the level of the right atrium and with the patient in the left lateral position. Thereafter, the heart rate and blood pressure were measured 1 min after standing up. Each test was performed five times to obtain a mean reading. Between each measurement the subject had 10 min of bed rest in the lateral position. 2.1. Statistics Statistical analysis was carried out using ANOVA for continuous normally distributed data and appropriate non-parametric tests for data that was not normally distributed. Analysis of variance for repeated measures was used to evaluate the possibility of significant time-based effects within groups. As none were found, all five measures for each patient were grouped and averaged. 3. Results Demographic data, drug therapy, and baseline cardiovascular data are shown in Table 1. The SBP and DBP at rest in the left lateral position were significantly higher in both PE and H women, compared with non-pregnant and normal pregnant women. The NP group had significantly lower resting heart rates than all other groups. The PC group had a significantly higher resting HR than the PE group. There were no significant differences between consecutive measures of SBP, DBP or HR in any of the groups, i.e. there was no time-based effect. The mean changes in each group in SBP, DBP and HR after a change from the left lateral to the erect position, are shown in Figs. 1–3. (A positive change in blood pressure or HR represents an increase in either parameter on adopting the erect
210
Non-pregnant controls (NP) Number Mean age (years) (S.D.) Height (cm) (S.D.) Weight (kg) (S.D.) Parity (range) Gravidity (range) Gest. age (weeks) Aldomet CCB CCBqAldomet Atenololqdiuretic SBP L (S.D.) DBP L (S.D.) PR L (S.D.)
17 30.6 (8.4) 164.1 (6.9) 58.6 (8.7) 0 (0–3) 0 (0–3) NyA Nil Nil Nil Nil 111.0 (8.8) 68.2 (7.4) 70.3 (10.7)
P
-0.05 NP)PC, PE, H -0.05 NP-PE, H
-0.05 NP-PC, PE, H
Normotensive (PC) 21 26.3 (5.7) 156.3 (6.7) 66.7 (17.5) 1 (0-3) 2 (1-6) 37.6 (3.0) Nil Nil Nil Nil 108 (13.5) 63.5 (10.8) 82.3 (14.1)
P
-0.05 PC)PE
Proteinuric hypertension (PE) 31 26.8 (6.6) 156.9 (6.7) 73.4 (19.5) 1 (0–4) 2 (1–5) 33.5 (3.7) 16 6 3 Nil 139.8 (20.3) 86.6 (17.3) 76.7 (12.9)
P
-0.05 PE)NP, PC -0.05 PE)NP, PC
Hypertension (H) 22 29.8 (6.8) 159.4 (6.4) 80.0 (20.3) 1 (0-4) 2 (1-5) 36.5 (3.1) 5 2 2 1 135.1 (19.4) 82.4 (13.8) 79.7 (14.9)
P
-0.05 H)PC, NP
-0.05 H)NP, PC -0.05 H)NP, PC
Statistical significance if P-0.05; S.D., standard deviation; Gest. age, gestational age; CCB, calcium channel blocker; SBP L, systolic blood pressure in the left lateral position; DBP L, diastolic blood pressure in the left lateral position; PR L, pulse rate in the left lateral position.
R.A. Dyer et al. / International Journal of Gynecology and Obstetrics 84 (2004) 208–213
Table 1 Demographic data, drug therapy, and baseline cardiovascular data
R.A. Dyer et al. / International Journal of Gynecology and Obstetrics 84 (2004) 208–213
q
Fig. 1. SBP, systolic blood pressure. *PC significantly greater than all other groups.
position.) The results may be summarized as follows: ● The PC group exhibited significantly greater mean changes (increases) in SBP than the NP, PE and H groups, when the erect position was adopted. The PE group exhibited significantly less of an increase in SBP than the H group. ● Both the H and the PC group showed significantly greater increases in DBP than the NP group. The PE patients showed a significantly smaller increase in DBP than the H group and
211
H significantly greater than PE.
a trend towards a smaller diastolic change than that seen in the PC group. ● There were no significant differences between HR changes when comparing the PC, NP and H groups. The PE group exhibited a significantly greater mean increase in HR on adopting the erect position than all other groups. 4. Discussion Early studies involving cardiovascular autonomic changes in pregnancy examined the effects of
Fig. 2. DBP, diastolic blood pressure. *H and PC significantly greater than NP.
q
H significantly greater than PE.
212
R.A. Dyer et al. / International Journal of Gynecology and Obstetrics 84 (2004) 208–213
Fig. 3. PR, pulse rate. *PE significantly greater than all other groups.
changes in position, employing simple tests such as changes in pulse and blood pressure in response to a change from the supine to the erect position, and to the Valsalva maneuver, as well as to changes in respiratory pattern w2–5x. Only one study has employed invasive monitoring in the form of pulmonary artery catheterization to demonstrate the response to an orthostatic maneuver in normal pregnant patients w1x. Measurements were made during the third trimester, and repeated 6 weeks postpartum in the same patients. Both during pregnancy and 6 weeks postpartum, cardiac output decreased during orthostasis. It was concluded that during pregnancy the increased blood volume resulted in less marked decreases in cardiac output during the orthostatic maneuver than postpartum. In the postpartum period, there was a greater rise in peripheral resistance during the maneuver than during pregnancy, which contributed to the maintenance of blood pressure that did not change significantly during orthostasis. The present study, involving four groups of patients (proteinuric hypertensives, non-proteinuric hypertensives, a normotensive pregnant control group, and a nonpregnant group) (Table 1), did not reflect the same changes in blood pressure as those described by Clark. The change from left lateral to the erect position induced significantly greater mean changes (and an increase) in the systolic and DBP in
the PC group than in the NP group (Figs. 1 and 2). As in Clark’s study, the HR increased in these two groups, but there were no significant between group differences (Fig. 3). There are some obvious differences between Clark’s study and our findings. All groups in our study showed a rise in DBP and a rise in HR that presumably reflects a sympathetic response and rising peripheral vascular resistance (Fig. 2). This is consistent with Clark’s findings. The increase in SBP seen in our study differed from Clark’s findings and may reflect a more immediate hemodynamic response than those measured by Clark, who assessed his subjects 10 min after assuming a change in posture. The PE group in the current study exhibited greater increases in HR in response to an orthostatic maneuver than the NP and PC groups (Fig. 3). In addition, they did not exhibit the same rise in SBP as did the PC group. The exaggerated change in HR rate may suggest a greater sympathetic response than seen in the PC patients. The absence of any change in systolic pressure may reflect the decreased intravascular volume and the already raised systemic vascular resistance in these patients. There is considerable evidence for altered cardiovascular autonomic control in pre-eclampsia. In an evaluation of autonomic function in pre-eclamptics in the third trimester, HR responses to deep
R.A. Dyer et al. / International Journal of Gynecology and Obstetrics 84 (2004) 208–213
breathing and standing up were less marked in severe pre-eclamptics than in the control group w4x. This was interpreted as a relative inability to regulate HR and blood pressure in response to postural alterations. These data are at variance with our findings, although the authors of this study showed that in mild pre-eclamptics, cardiovascular reflexes were found to be normal and suggested that autonomic dysfunction is a condition that may evolve during the pathogenesis of severe disease. Another study demonstrated that pre-eclamptic women reached their maximal HR in a shorter period of time after adopting the erect position, but did not sustain a HR as high as normotensive pregnant patients w3x. Overall, our data are therefore not inconsistent with previous work, although the exaggerated tachycardia has not been previously described. Alternative explanations for the differences apparent between pre-eclamptic women and controls may be due to changes in baroreceptor function. Early studies have demonstrated abrupt and profound reductions in blood pressure in response to hydralazine in women with severe pre-eclampsia which was attributed to baroreceptor dysfunction by the authors w2x. More recent publications describe computerized spectral analysis methods for heart rate variability (HRV) estimation as a measure of sympathovagal balance w5–7x. In general, high frequency components of the HRV are evidence of vagal predominance (demonstrated by a marked HRV in response to deep breathing), while low frequency components suggest a predominance of sympathetic activity (reflecting blood pressure oscillations). Pre-eclamptics have been shown to be characterized by a significantly reduced high frequency peak compared with healthy pregnant patients, suggesting decreased vagal control of the heart w5x. A recent investigation employing frequency domain analysis of short-term, stationary R–R intervals suggested that pre-eclampsia may be associated with increased sympathetic and decreased parasympathetic control of the heart w6x. However, another study suggested that baroreflex gain, evaluated by cross-spectral
213
analysis of SBP and pulse interval, was found to be lower in pre-eclamptic women both compared with non-pregnant and healthy pregnant subjects w7x. These findings are consistent with our data with respect to HR changes, although baroreflex responses were not obviously impaired in the preeclamptic women included in the current study. The literature thus contains conflicting data regarding the autonomic changes that characterize pre-eclampsia. The reasons for these differences may lie in variations in methodology and differences in the severity of pre-eclampsia studied. Drug therapy may give rise to confounding effects. Overall, our data suggest that proteinuric hypertensives exhibit altered autonomic compensatory mechanisms from those of healthy parturients, with particular reference to the heart rate response to standing. References w1x Clark SL, Cotton DB, Pivarnik JM, Lee W, Hankins GDV, Benedetti TJ, et al. Position change and central hemodynamic profile during normal third-trimester pregnancy and post partum. Am J Obstet Gynecol 1991;164:883 –887. w2x Wasserstrum N, Kirshon B, Rossavik IK, Willis RS, Moise KJ, Cotton DB. Implications of sino-aortic baroreceptor reflex dysfunction in severe pre-eclampsia. Obstet Gynecol 1989;74:34 –38. w3x Wouters EJM, Jaspers WJM, Kurver PJ, de Jong PA. Autonomic heart-rate control in response to standing in toxaemic and normotensive primigravid pregnancies. Eur J Obstet Gynecol Reprod Biol 1984;16:309 –314. w4x Airaksinen KEJ, Kirkinen P, Takkunen JT. Autonomic dysfunction in severe pre-eclampsia. Eur J Obstet Gynecol Reprod Biol 1985;19:269 –276. w5x Eneroth-Grimfors E, Westgren M, Ericson M, IhrmanSandahl C, Lindblad LE. Autonomic cardiovascular control in normal and pre-eclamptic pregnancy. Acta Obstet Gynecol Scand 1994;73:680 –684. w6x Yang CCH, Chao T-C, Kuo TBJ, Yin C-SY, Chen HI. Pre-eclamptic pregnancy is associated with increased sympathetic and decreased parasympathetic control of heart rate. Am J Physiol Heart Circ Physiol 2000;278(4):H1269 –H1273. w7x Molino P, Veglio F, Genova GC, Melchio R, Benedetto C, Chiarolini L, et al. Baroreflex control of heart rate is impaired in pre-eclampsia. J Hum Hypertens 1999;13:179 –183.