Physiology and Pathophysiology of Heart Rate and Blood Pressure Variability in Humans: Is Power Spectral Analysis Largely An Index of Baroreflex Gain?

Abstract

1. It is often assumed that the power in the low- (around 0.10 Hz) and high-frequency (around 0.25 Hz) bands obtained by power spectral analysis of cardiovascular variables reflects sympathetic and vagal tone [corrected] respectively. An alternative model attributes the low-frequency band to a resonance in the control system that is produced by the inefficiently slow time constant of the reflex response to beat-to-beat changes in blood pressure effected by the sympathetic (with or without the parasympathetic) arm(s) of the baroreflex (De Boer model). 2. We have applied the De Boer model of circulatory variability to patients with varying baroreflex sensitivity to patients with varying baroreflex sensitivity and one normal subject, and have shown that the main differences in spectral power (for both low and high frequency) between and within subjects are caused by changes in the arterial baroreflex gain, particularly for vagal control of heart rate (R-R interval) and left ventricular stroke output. We have computed the power spectrum at rest and during neck suction (to stimulate carotid baroreceptors). We stimulated the baroreceptors at two frequencies (0.1 and 0.2 Hz), which were both distinct from the controlled respiration rate (0.25 Hz), in both normal subjects and heart failure patients with either sensitive or poor baroreflex control. 3. The data broadly confirm the De Boer model. The low-frequency (0.1 Hz) peak in either R-R or blood pressure variability) was spontaneously generated only if the baroreflex control of the autonomic outflow was relatively intact.(ABSTRACT TRUNCATED AT 250 WORDS)

Slow oscillations in blood pressure via a nonlinear feedback model

“…In comparison with the power of the faster oscillation in heart rate associated with respiration, there have been numerous papers reporting changes in sympatho-vagal balance in such varied conditions as anesthesia (20), sleep (3), and the menstrual cycle (36). A mounting number of studies indicates that this hypothesis is flawed on several points, and it is more probable that the 0.1-Hz oscillation in heart rate provides an index of baroreflex gain (5,38,39). Our model supports this hypothesis and may explain why some stimuli such as coronary occlusion, which increases mean SNA levels, was associated with reductions in power at 0.1 Hz in heart rate (19).…”

“…Additionally, using a nonlinear feedback model, it is straightforward to show that the variation in frequency of the oscillations in blood pressure in rats (0.4 Hz), rabbits (0.3 Hz), and humans (0.1 Hz) is primarily due to scaling effects of conduction times between species. sympathetic nervous system; baroreflex; stability; describing function; artificial neural network IT IS WELL ESTABLISHED that blood pressure in humans can contain a distinct oscillation at 0.1 Hz, often referred to as the Mayer wave (26,38). Experiments in a variety of animal models have shown that this oscillation is due to the action of the sympathetic nervous system on the vasculature.…”

“…IT IS WELL ESTABLISHED that blood pressure in humans can contain a distinct oscillation at 0.1 Hz, often referred to as the Mayer wave (26,38). Experiments in a variety of animal models have shown that this oscillation is due to the action of the sympathetic nervous system on the vasculature.…”

Endurance training, overtraining and baroreflex sensitivity in female athletes

“…(1995) have suggested that reduced central gain of the arterialbaroreflex regulation of heart rate is responsible for the de~reased HR response to phenylephrine injection in trained rats, without changes in tIle reactivity of baroreceptor afferents. It is well justified to study baroreflex sensitivity changes induced by endurance training and overtraining because endurance training has been reported to increase vagal tone and maximal oxygen uptake (Seals & Chase, 1989), which are correlates of baroreflex sensitivity (Sleight et at., 1995). We found that RRI LFP increased in the ETG during the training period as a possible marker of increased cardiac sympathetic modulation at rest due to excessive training (Akselrod et at., 1985;Pagani et at., 1986).…”

Autonomic cardiovascular regulation in subjects with acute mountain sickness

“…Spectral analysis of variability in the R-R interval is a recognized tool that allows quantification of the oscillatory components, which in short-term recordings appear mainly organized into two frequency bands: low-frequency (LF, ϳ0.1 Hz) and high-frequency (HF, Ͼ0.15 Hz) respiratory bands. Although the HF rhythm primarily reflects the respirationdriven vagal modulation of sinus rhythm (32a), the nonrespiratory LF rhythm appears to have a widespread neural genesis (26) and, in normalized units (NU), apparently mainly reflects the sympathetic modulation of the heart (23, 26, 32a), as well as the baroreflex responsiveness to the beat-to-beat variations in arterial blood pressure (BP) (30). During exposure to high altitude, R-R variability is reduced with a relative increase in the LF component (2,12,13), suggesting an increased sympathetic modulation of the sinus node in response to hypobaric hypoxia.…”