Mechanism of blood pressure and R‐R variability: insights from ganglion blockade in humans

Abstract

Spontaneous blood pressure (BP) and R-R variability are used frequently as 'windows' into cardiovascular control mechanisms. However, the origin of these rhythmic fluctuations is not completely understood. In this study, with ganglion blockade, we evaluated the role of autonomic neural activity versus other 'non-neural' factors in the origin of BP and R-R variability in humans. Beat-to-beat BP, R-R interval and respiratory excursions were recorded in ten healthy subjects (aged 30 ± 6 years) before and after ganglion blockade with trimethaphan. The spectral power of these variables was calculated in the very low (0.0078-0.05 Hz), low (0.05-0.15 Hz) and high (0.15-0.35 Hz) frequency ranges. The relationship between systolic BP and R-R variability was examined by cross-spectral analysis. After blockade, R-R variability was virtually abolished at all frequencies; however, respiration and high frequency BP variability remained unchanged. Very low and low frequency BP variability was reduced substantially by 84 and 69 %, respectively, but still persisted. Transfer function gain between systolic BP and R-R interval variability decreased by 92 and 88 % at low and high frequencies, respectively, while the phase changed from negative to positive values at the high frequencies. These data suggest that under supine resting conditions with spontaneous breathing: (1) R-R variability at all measured frequencies is predominantly controlled by autonomic neural activity; (2) BP variability at high frequencies (> 0.15 Hz) is mediated largely, if not exclusively, by mechanical effects of respiration on intrathoracic pressure and/or cardiac filling; (3) BP variability at very low and low frequencies (< 0.15 Hz) is probably mediated by both sympathetic nerve activity and intrinsic vasomotor rhythmicity; and (4) the dynamic relationship between BP and R-R variability as quantified by transfer function analysis is determined predominantly by autonomic neural activity rather than other, non-neural factors.

Blood pressure variability and prognosis in acute ischemic stroke with vascular compression on the rostral ventrolateral medulla (RVLM)

“…8 In addition, the increased sympathetic nerve activity may induce high blood pressure variability because it was reduced after ganglion blockade with trimethaphan. 28 In parallel to this response, when sympathetic nerve activity increases, the baroreflex counteracts this activation in normal subjects. However, it is still unknown whether the increase in sympathetic nerve activity is caused by increased sympathetic nerve traffic, increased vascular sensitivity, or impaired baroreflex buffering in patients with RVLM vascular compression.…”

Evidence of a myogenic response in vasomotor control of forearm and palm cutaneous microcirculations

“…This project was a component of a larger project of which data have been previously presented (24,25).…”

“…1). The absence and/or attenuation of the heart rate response demonstrated the efficacy of ganglionic blockade (19,24,25). A minimum of 2 min elapsed between successive VMs.…”

“…Data during this phase of the VM were analyzed because of sustained decreases in arterial blood pressure after ganglionic blockade (24). Cutaneous vascular conductance at baseline (CVC base) was calculated from the ratio of skin blood flow and mean arterial blood pressure.…”

A simple deep breathing test reveals altered cerebral autoregulation in type 2 diabetic patients

“…Blood pressure oscillations induced by breathing are predominantly due to the mechanical effects of fluctuations in cardiac stroke volume [14]. Slow breathing at six cycles per minute (0.1 Hz) generates oscillations in blood pressure at the same frequency that are transmitted onto the CBFV [12].…”