In this study, we tested the hypothesis that the neural control of circulation in humans undergoes continuous but in part predictable changes throughout the day and night. Dynamic 24-hour recordings were obtained in two groups of ambulant subjects. In 18 hospitalized patients free to move, direct high-fidelity arterial pressures and electrocardiograms were recorded, and in an additional 28 nonhospitalized subjects, only electrocardiograms were obtained. Spectral analysis of systolic arterial pressure and of RR interval variabilities provided quantitative markers of sympathetic and vagal control of the sinus node and of sympathetic modulation of vasomotor tone. With this approach, the low-frequency (-0.1 Hz) component of RR interval and systolic arterial pressure variabilities is considered a marker primarily of sympathetic activity, whereas the high-frequency (-0.25 Hz) component of RR interval variability, related to respiration, seems to be a marker primarily of vagal activity. We observed a pronounced and consistent reduction in the markers of sympathetic activity and an increase in those of vagal activity during the night. In the invasive studies, while the subjects were still lying in bed after waking up, the markers of sympathetic activity rose rapidly and concomitantly with a simultaneous vagal withdrawal. Noninvasive studies confirmed the early morning rise of the markers of sympathetic activity and the circadian pattern of sympathovagal balance. These data indicate that the ominously increased rate of cardiovascular events in the morning hours may reflect the sudden rise of sympathetic activity and the reduction of vagal tone. (Circulation 1990;81:537-547
Mitral valve areas determined by two-dimensional planimetry, pressure half-time and proximal flow convergence region reliably correlated with size of the anatomic orifice. The flow area method provided a less reliable correlation.
Right ventricular dysfunction and abnormal HRV may represent the early features of cardiac disease in thalassemic patients with no evidence of ventricular dysfunction at routine evaluation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.