Increased respiratory modulation of cardiovascular control reflects improved blood pressure regulation in pregnancy.

Hypertensive pregnancy disorders put the maternal-fetal dyad at risk and are one of the leading causes of morbidity and mortality during pregnancy. Multiple efforts have been made to understand the physiological mechanisms behind changes in blood pressure. Still, to date, no study has focused on analyzing the dynamics of the interactions between the systems involved in blood pressure control. In this work, we aim to address this question by evaluating the phase coherence between different signals using wavelet phase coherence. Electrocardiogram, continuous blood pressure, electrocardiogram-derived respiration, and muscle sympathetic nerve activity signals were obtained from ten normotensive pregnant women, ten normotensive non-pregnant women, and ten pregnant women with preeclampsia during rest and cold pressor test. At rest, normotensive pregnant women showed higher phase coherence in the high-frequency band (0.15-0.4 Hz) between muscle sympathetic nerve activity and the RR interval, blood pressure, and respiration compared to non-pregnant normotensive women. Although normotensive pregnant women showed no phase coherence differences with respect to hypertensive pregnant women at rest, higher phase coherence between the same pairs of variables was found during the cold pressor test. These results suggest that, in addition to the increased sympathetic tone of normotensive pregnant women widely described in the existing literature, there is an increase in cardiac parasympathetic modulation and respiratory-driven modulation of muscle sympathetic nerve activity and blood pressure that could compensate sympathetic increase and make blood pressure control more efficient to maintain it in normal ranges. Moreover, blunted modulation could prevent its buffer effect and produce an increase in blood pressure levels, as observed in the hypertensive women in this study. This initial exploration of cardiorespiratory coupling in pregnancy opens the opportunity to follow up on more in-depth analyses and determine causal influences.

Comparison of a tonometric with an oscillometric blood pressure monitoring device over 24 hours of ambulatory use.

PURPOSE: Multiple devices capable of measuring ambulatory blood pressure without cuffs have been recently developed and it is required that they offer high-accuracy measurements. The purpose of this prospective study was to compare the performance of a tonometric blood pressure monitor with that of an oscillometric cuff-based device used as a reference in healthy and hypertensive subjects over 24 hours of ambulatory use. MATERIALS AND METHODS: Conventional oscillometric cuff-based device (Oscar 2; Sun Tech Medical) was placed in the left arm of 33 subjects, and a watch-type device based on the tonometric method (Bpro; HealthSTATS International, Singapore) was positioned in the right wrist. Both devices were synchronized to measure simultaneously over 24 hours. RESULTS: The difference between the means over 24 hours of the oscillometric and the tonometric devices was -0.9 mmHg for SBP and -4.5 mmHg for DBP; the standard deviations were 14.7 and 12.2 mmHg, respectively. Greater differences in bias and dispersion were observed overnight than during the daytime. The accuracy of the tonometric device for diagnosing hypertension was 75% and for detecting the non-dipper profile, 48%. CONCLUSION: The test device presented a high disagreement (especially during the night) compared to the oscillometric cuff-based device against which it was initially calibrated. This disagreement resulted in limited accuracy for diagnosing patients with suspected arterial hypertension and detecting non-dipper profiles.

Acute Cardiovascular Responses to a Session of Bikram Yoga: A Pilot Uncontrolled Trial.

INTRODUCTION: Main cardiovascular parameters such as heart rate (HR), blood pressure, and myocardial oxygen consumption (MOC) are tightly regulated by a multifactorial, nonlinear control system. Increased HR because of physical activity is often accompanied by an increase in blood pressure. Postural changes have an effect on the baroreceptors, and stretching exercises and isometric contractions modulate muscle mechanoreceptors eliciting increases in blood pressure. However, a hot environment increases the core temperature inducing vasodilation and plasma volume changes that might contribute to a drop in blood pressure. During the practice of Bikram yoga, all these factors converge and little is known about the resulting changes in blood pressure and MOC. METHODS: Sixteen apparently healthy female volunteers, regular practitioners of Bikram yoga, were evaluated during a 90 min session. Systolic blood pressure (SBP) and diastolic blood pressure (DBP) were measured immediately after each posture and HR was measured continuously during the practice. RESULTS: HR and estimated MOC increased significantly over baseline during the exercise (+62.3% and +63.6%, respectively). HR mean value across the entire Bikram yoga session was 126.6 ± 14.3 bpm reaching a maximum of 168.1 ± 20.2 bpm. SBP was not significantly increased over baseline at any time during the practice with a mean value of 117.0 ± 10.1 mmHg and DBP was significantly decreased over baseline most of the time (-10.1%, mean 71.2 ± 7.3 mmHg) with particular decline toward the end of the practice during the floor postures. CONCLUSIONS: DBP during the practice of Bikram yoga was significantly different from that previously reported for nonheated Hatha yoga for normotensive subjects. Further studies evaluating the same group at both conditions are needed to better characterize the magnitude of the changes in HR, SBP, DBP, and MOC.