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Spontaneous ‘baroreflex sequences’ occur as deterministic functions of breathing phase
Author(s) -
Rothlisberger Brian W.,
Badra Leslie J.,
Hoag Jeffrey B.,
Cooke William H.,
Kuusela Tom A.,
Tahvanainen Kari U.O.,
Eckberg Dwain L.
Publication year - 2003
Publication title -
clinical physiology and functional imaging
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.608
H-Index - 67
eISSN - 1475-097X
pISSN - 1475-0961
DOI - 10.1046/j.1475-0961.2003.00489.x
Subject(s) - baroreflex , medicine , expiration , supine position , breathing , blood pressure , anesthesia , respiration , periodic breathing , cardiology , heart rate , apnea , anatomy , respiratory system
Summary Parallel increases or decreases of systolic pressures and R–R intervals occur spontaneously in healthy resting humans, and are thought to be expressions of vagal baroreflex physiology. We studied ten healthy supine young adults, and tested the null hypothesis that spontaneous baroreflex sequences are distributed uniformly throughout the breathing cycle. We recorded the electrocardiogram, photoplethysmographic arterial pressure, respiration (pneumobelt), and peroneal nerve muscle sympathetic activity in supine subjects who breathed spontaneously, or held their breaths in inspiration after 2 min of hyperventilation with 100% oxygen. We analysed pairs of three or more increasing or decreasing systolic pressures and R–R intervals with linear regression, and related the gain and timing of the onset of such sequences to the phase of respiration, and to preceding muscle sympathetic nerve activity. We found that baroreflex sequences occur erratically, at a frequency about one‐third that of breathing. However, when baroreflex sequences do occur, the timing of their onset is dictated by the phase of respiration. Parallel increases of systolic pressures and R–R intervals (‘up’ sequences) begin just before and after the beginning of expiration, and parallel decreases of systolic pressures and R–R intervals (‘down’ sequences) begin during late expiration and inspiration. Average gains of up and down baroreflex sequences triggered by muscle sympathetic bursts are comparable during breathing and apnoea. However, the latencies between sympathetic bursts and baroreflex sequences are less during breathing than during apnoea. We propose that parallel systolic pressure – R–R interval sequences are expressions of arterial baroreflex physiology, and that the nearly fixed timing of such sequences within breaths reflects simply respiratory gating of muscle sympathetic bursts.