EFFECTS OF DYNAMIC EXERCISE ON CARDIOVASCULAR REGULATION DURING LOWER-BODY NEGATIVE-PRESSURE

The purpose of this study was to compare the cardiovascular control me chanisms that defend arterial blood pressure against blood pooling bet ween rest and moderate dynamic exercise. We studied ten physically act ive men during rest and five 12-min graded supine cycle ergometer exer cise bouts with and without application of LBNP in 25-degrees-C and 35 -degrees-C. Exercise intensities were 10, 50, and 100 watts (W), each for 4 min, and LBNP was applied at 0 (control), -20, -40, and -60 mm H g in 25-degrees-C and -40 mm Hg in 35-degrees-C. At rest, cardiac stro ke volume (SV) decreased from 120 +/- 5 ml during control to 94 +/- 6, 67 +/- 5 and 49 +/- 3 ml during -20, -40, and -60 mm Hg LBNP, respect ively, and to 55 +/- 3 ml during -40 mm Hg at 35-degrees-C. Exercise e levated SV toward the control level during LBNP due to muscle pumping action. Heart rate (HR) did not increase significantly during applicat ion of LBNP until SV decreased by 20-25 ml during LBNP, both during re st and exercise. The magnitude of HR increase per decrease in SV, once an increase in HR occurred, was similar between rest and exercise, re gardless of exercise intensity. The change in total peripheral resista nce (TPR) with respect to SV was linear, confirming that peripheral va scular adjustments were proportional to changes in the heart's preload . The slopes of the TPR-SV relation were similar during rest and exerc ise, although shifted to the left with increasing exercise intensity. Our results support the notion that the control characteristics of art erial blood pressure regulation are similar during rest and moderate d ynamic exercise.