Changes in baroreceptor sensitivity for heart rate during normotensive pregnancy and the puerperium

Abstract

Normal pregnancy is associated with marked changes in cardiovascular haemodynamics, which in part may be due to changes in autonomic control mechanisms. Baroreflex sensitivity for heart rate (BRS) was calculated in the supine and standing positions using power spectral analysis of pulse interval (PI) and systolic blood pressure (SBP) in 16 normotensive pregnant women and 10 normotensive non-pregnant controls. The pregnant women were studied on three occasions during their pregnancy (early, mid- and late gestation) and once during the puerperium. Supine total SBP variability increased between early and late pregnancy by 79% [95% confidence intervals (CI) 30%, 145%; P<0. 001], and supine high-frequency PI variability decreased by 75% (CI 51%, 88%; P<0.001). Supine BRS fell by 50% (P<0.001), with values returning to early-pregnancy levels in the puerperium, which were similar to those recorded in the control group. Standing SBP variability and BRS values were unchanged during pregnancy and post partum. The low/high frequency ratio of PI variability, taken as a surrogate measure of sympathovagal balance, increased by 137% (CI 42%, 296%; P<0.01) in the supine but not the standing position from early to late pregnancy. This was due to a decrease in high-frequency variability rather than to an increase in low-frequency variability, suggesting that these changes may have been due to vagal withdrawal rather than increased sympathetic activity. Normotensive pregnancy is associated with a marked decrease in supine BRS, although the exact mechanisms for these changes remain unclear. Further studies are required to define whether changes in BRS and sympathovagal tone in early pregnancy can be used to predict the onset of pregnancy-induced hypertension.

Carotid artery stiffening does not explain baroreflex impairment in pre-eclampsia

“…In this latter study, similar to ours, the subjects were older and their mean BRS value was half of that in the study by Silver et al [17]. In all studies, BRS values increased after delivery in both hypertensive patients and normotensive controls, findings that are in line with our present data [7,18].…”

Alteration of skin laser-Doppler flux response to local cooling in gestational hypertension

“…HF) coefficient and also the LF band power remained unchanged in women with normal pregnancy, indicating that the higher heart rate values in healthy pregnant females is caused by the predominance of sympathetic cardiac control as a result of decreased parasympathetic activity. This is further supported by the decreased baroreflex sensitivity in the healthy pregnant females observed in present study that is in agreement with the results of Blake and associates [4].…”

“…Nevertheless, our results in resting conditions did not reveal any significant difference between the The results of HRV analysis in resting conditions are in accordance with the majority of studies involving nonhypertensive pregnancy, which have shown a decrease in both HF power values [2] and an increase in LF/HF coefficient [4,8,19,28] for non-hypertensive pregnant women. These findings are interpreted as a decreased parasympathetic activity level.…”

“…Most studies dealing with autonomic nervous system changes during normal pregnancy are based on heart rate and blood pressure variability comparing non-pregnant with pregnant women. However, the results are controversial with regard to the estimated level of sympathetic and parasympathetic reactivity based on standardized heart variability indices [2,4,8,19,28].…”

Does the menstrual cycle influence the sensitivity of vagally mediated baroreflexes?

“…Blake et al [17] and Silver et al [18] reported reductions of baroreflex sensitivity of 50 % and 40 % in pregnant, normotensive women. Although baroreflex sensitivity is not altered by chronic oestrogen treatment in non-pregnant rabbits [19], cardiovagal baroreflex sensitivity decreases in non-pregnant young women taking oral contraceptives [20].…”