Daytime variability in carotid baroreflex function in healthy human subjects.

Area of Science:

• Cardiovascular Physiology
• Chronobiology
• Autonomic Nervous System Function

Background:

• Arterial baroreceptors regulate blood pressure variability, but circadian blood pressure changes persist.
• The daily fluctuations in blood pressure suggest potential variations in baroreflex responses throughout the day.

Purpose of the Study:

• To investigate whether carotid baroreflex responses exhibit diurnal variations.
• To assess how reflex sensitivity and operating points change across different times of the day.

Main Methods:

• Carotid baroreflex stimulation and inhibition were performed using neck chamber pressure and suction in 14 healthy subjects.
• Measurements included cardiac interval (RR), mean arterial pressure (MAP), and vascular resistance (VR) at three-hourly intervals from 09:00 to 21:00.
• Stimulus-response curves were analyzed to determine baroreflex sensitivity (maximal slope) and operating point (OP).

Main Results:

• Baroreflex sensitivity for vascular resistance control was highest at 09:00 and significantly lower at later times.
• The operating point for mean arterial pressure control was lowest in the morning.
• Baroreflex sensitivity correlated with mean pressure, and operating points correlated with prevailing mean arterial pressure.

Conclusions:

• Carotid baroreflex function demonstrates significant diurnal variation.
• Higher baroreflex sensitivity and lower blood pressure in the morning may be linked to these daily functional changes.
• These findings suggest a potential role for diurnal baroreflex variation in long-term blood pressure regulation.