Modes of baroreceptor-sympathetic coordination.

Area of Science:

• Neuroscience
• Physiology
• Nonlinear Dynamics

Background:

• The cardiac-related rhythm in sympathetic nerve discharge (SND) is a key physiological phenomenon.
• The precise mechanism driving this rhythm, particularly its relationship with heart beat, remains under investigation.
• Baroreceptor afferent nerve activity is hypothesized to influence central oscillators controlling SND.

Purpose of the Study:

• To test the hypothesis that pulse-synchronous baroreceptor afferent nerve activity forces a central oscillator to the heart's frequency.
• To investigate the phase relations between brachial arterial pulse and cardiac-related sympathetic nerve activity.
• To elucidate the role of blood pressure in modulating the cardiac-related rhythm of SND.

Main Methods:

• Time series analysis of brachial arterial pulse (AP) and cardiac sympathetic nerve (CN) activity in urethane-anesthetized cats.
• Cycle-by-cycle measurements of systolic blood pressure, heart period, CN burst amplitude, and phase angles.
• Manipulation of blood pressure via phenylephrine infusion and abdominal aortic obstruction.

Main Results:

• Increased blood pressure led to transitions from no phase-locking to variable phase-locking or phase walk between CN activity and AP.
• Phase-locking strength increased with blood pressure, altering the interval between systole and CN activity.
• Abrupt increases in blood pressure caused sharp phase transitions in CN activity relative to AP, even without heart rate changes.

Conclusions:

• The cardiac-related rhythm in SND is best described as a forced nonlinear oscillation.
• This rhythm is not due to periodic inhibition of random activity but rather the forcing of a central oscillator by pulse-synchronous baroreceptor input.
• Findings support a dynamical systems perspective on the neural control of circulation.