Aortic-cardiac reflex during dynamic exercise.

Abstract

We investigated the aortic-cardiac reflex during low-intensity cycling in 10 healthy volunteers. Baroreflex function was assessed by the ratio of change in heart rate to mean arterial pressure (delta HR/delta MAP) during phenylephrine (PE) infusion. The ratio obtained during PE combined with low-level lower body negative pressure (LBNP) and calculated neck pressure (NP) was assessed as the gain of the aortic-cardiac reflex. Exercise (approximately 25% maximal O2 uptake or 25 +/- 2 W) significantly increased HR from 64 +/- 2 to 98 +/- 2 beats/min, MAP from 90 +/- 3 to 98 +/- 3 mmHg, cardiac output from 6.6 +/- 0.5 to 12.0 +/- 1.4 l/min, and O2 uptake from 3.8 +/- 0.2 to 10.4 +/- 0.6 ml.min-1.kg-1. However, delta MAP (+11.8 +/- 0.4 vs. + 11.3 +/- 0.8 mmHg), delta HR (-12.7 +/- 2 vs. -12.9 +/- 2 beats/min), and delta HR/delta MAP (1.10 +/- 0.19 vs. 1.15 +/- 0.15 beats.min-1.mmHg-1) were not statistically different between rest and exercise during PE. Although PE significantly increased central venous pressure in both supine rest (from 6.7 +/- 0.7 to 10.4 +/- 0.7 mmHg) and exercise (5.8 +/- 0.8 to 8.6 +/- 0.9 mmHg) conditions, when LBNP (-15 +/- 2 vs. -16 +/- 1 Torr for rest vs. exercise) was applied, both rest and exercise central venous pressures were returned to the preinfusion baseline values, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)