Spontaneous 'baroreflex sequences' occur as deterministic functions of breathing phase

Area of Science:

• Cardiovascular physiology
• Autonomic nervous system regulation
• Respiratory influences on cardiovascular control

Background:

• Spontaneous increases/decreases in systolic pressure and R-R intervals suggest vagal baroreflex activity.
• Previous research hypothesized uniform distribution of baroreflex sequences throughout the breathing cycle.

Purpose of the Study:

• To test the hypothesis that spontaneous baroreflex sequences are uniformly distributed across the respiratory cycle.
• To investigate the influence of respiration and muscle sympathetic nerve activity on the timing and gain of baroreflex sequences.

Main Methods:

• Recording of ECG, arterial pressure, respiration, and muscle sympathetic nerve activity in healthy adults.
• Analysis of baroreflex sequences (three or more pressure/R-R interval changes) using linear regression.
• Correlation of sequence timing and gain with respiratory phase and sympathetic activity during spontaneous breathing and apnea.

Main Results:

• Baroreflex sequences occurred infrequently, approximately one-third the breathing rate.
• Sequence onset timing was strongly correlated with the respiratory phase.
• Increases in systolic pressure/R-R intervals initiated near the start of expiration; decreases initiated during late expiration/inspiration.
• Baroreflex sequence gain was similar during breathing and apnea, but latency to sympathetic bursts was shorter during breathing.

Conclusions:

• Spontaneous systolic pressure-R-R interval sequences reflect arterial baroreflex function.
• Respiratory gating of muscle sympathetic nerve activity dictates the near-fixed timing of these baroreflex sequences within breaths.