RIGHT ATRIAL PRESSURE AND FOREARM BLOOD-FLOW DURING PROLONGED EXERCISE IN A HOT ENVIRONMENT

Right atrial pressure (RAP) at rest is known to be reduced by an incre ase in skin blood flow (SkBF) in a hot environment. However, there is no clear evidence that this is so during exercise. To clarify the effe ct of the increase in SkBF on RAP during exercise, we measured forearm blood flow (FBF) (as an index of SkBF) and RAP continuously using a S wan-Ganz catheter in five male volunteers exercising on a cycle ergome ter at 60% of peak aerobic power for 50 min in a hot environment (30 d egrees C, relative humidity 20%). Cardiac output increased from 5.5 +/ - 0.2 l/min at rest to 17.9 +/- 1.2 l/min (mean +/- SE, P < 0.01) in t he first 10 min of exercise and then remained steady until the end of exercise. FBF did not change significantly during the first 5 min, but then increased from 2.7 +/- 0.5 ml/100 ml per min at rest to 10.8 +/- 1.7 ml/100 ml per min (P < 0.001) by 25 min as pulmonary arterial blo od temperature (T-b) rose from 37.0 +/- 0.1 degrees C to 38.1 +/- 0.1 degrees C (P < 0.001). FBF then reached a plateau, despite a continuin g increase in T,. RAP increased significantly from 4.3 +/- 0.8 to 7.6 +/- 1.2 mm Hg (P < 0.001) during the first 5 min of exercise and then gradually declined to 6.1 +/- 1.0 mm Hg by 25 min (P < 0.001 vs. 5 min ) and further to 5.7 +/- 1.0 mm Hg by 50 min, a value not significantl y higher than at rest. This reduction in RAP during exercise was signi ficantly correlated with the increase in FBF (r = -0.97, P < 0.001) wi th a regression equation of RAP = -0.25XFBF + 8.8. These results sugge st that the decrease in RAP after 5 min exercise was caused by an incr ease in SkBF during exercise in a hot environment.