Blood pressure and heart rate variability analysis of orthostatic challenge in normal human pregnancies

Abstract

The aim of the present study was to evaluate pregnancy-related changes in autonomic regulatory functions in healthy subjects. We studied cardiovascular autonomic responses to head-up tilt (HUT) in 28 pregnant women during the third trimester of pregnancy and 3 months after parturition. The maternal ECG and non-invasive beat-to-beat blood pressure were recorded in the horizontal position (left-lateral position) and during HUT in the upright position. Stroke volume was assessed from blood pressure signal by using the arterial pulse contour method. Heart rate variability (HRV) was analysed in frequency domain, and baroreflex sensitivity by the cross-spectral and the sequence methods. In the horizontal position, all frequency components of HRV were lower during pregnancy than 3 months after parturition (P < 0.01 to <0.001), while pregnancy had no influence on normalized low frequency and high frequency powers. During pregnancy haemodynamics was well balanced with only minor changes in response to postural change while haemodynamic responses to HUT were more remarkable after parturition. In pregnant women HRV and especially its very low frequency component increased in response to HUT, whereas at 3 months after parturition the direction of these changes was opposite. Parasympathetic deactivation towards term is likely to contribute to increased heart rate and cardiac output at rest, whereas restored sympathetic modulation with modest responses may contribute stable peripheral resistance and sufficient placental blood supply under stimulated conditions. It is important to understand cardiovascular autonomic nervous system and haemodynamic control in normal pregnancy before being able to judge whether they are dysregulated in complicated pregnancies.

Phase Synchronization of Hemodynamic Variables at Rest and after Deep Breathing Measured during the Course of Pregnancy

“…However, in agreement to earlier observations [17], [46], respiratory frequency remained unaltered throughout pregnancy, apart from increased tidal volume leading to an increased minute volume. The analysis of BRS using the sequence method provides an index of autonomic nervous activity on RRI.…”

“…Our analysis suggests that the increase of HR throughout normal pregnancy is mainly driven by decreased parasympathetic activity, which confirms earlier observations [46]. Ekholm et al found decreased parasympathetic responsiveness in early and mid-pregnancy with some restoration in the third trimester, along with diminished HRV, suggesting decreased parasympathetic and/or increased sympathetic nervous system tone [44], [47].…”

A study on cardiac autonomic modulation during pregnancy by non-invasive heart rate variability measurement

“…Similar conclusions were obtained by considering the changes in LF/HF ratio. Signifi cant reduction in RMSSD, NN50 count, pNN50% and HF (ms Heiskanen et al's., [15] study showed that in normal pregnancy, the increment of the heart rate could be partially associated with the inhibition of resting parasympathetic activity connected with an increment of the sympathetic modulation but during the 3 rd third trimester of pregnancy there could be a parasympathetic deactivation instead of an increment of the sympathetic activity (under unstimulated conditions) even when the head-up tilt test induce changes in the parasympathetic activity and the sympathovagal balance.…”

Assessment of venous hemodynamics and volume homeostasis during pregnancy: recommendations of the International Working Group on Maternal Hemodynamics

“…This effect is very prominent at the level of the hepatic veins (HV), in which the first‐trimester triphasic venous pulse wave shifts to a completely flat pattern during the late second and third trimesters. These changes take place alongside important physiological gestational adaptations of the maternal body, among which are an increase in venous return and intravascular volume by altered renal function (vascular perfusion and drainage, glomerular and tubular function, hormonal production and response), a coordinated balanced change in baroreflex sensitivity of the heart and vasculature and raised external venous compression by an increase in intra‐abdominal pressure. The latter also contributes to the development of varicose veins and physiological malleolar edema during the course of pregnancy.…”