AGE ALTERS REGIONAL DISTRIBUTION OF BLOOD-FLOW DURING MODERATE-INTENSITY EXERCISE

During dynamic exercise in warm environments, requisite increases in s kin and active muscle blood flows are supported by increasing cardiac output (Q(c)) and redistributing flow away from splanchnic and renal c irculations. To examine the effect of age on these responses, six youn g (Y; 26 +/- 2 yr) and six older (O; 64 +/- 2 yr) men performed uprigh t cycle exercise at 35 and 60% of peak O-2 consumption (VO2peak) in 22 and 36 degrees C environments. To further isolate age, the two age gr oups were closely matched for VO2peak, weight, surface area, and body composition. Measurements included heart rate, Q(c) (CO2 rebreathing), skin blood flow (from increases in forearm blood flow (venous occlusi on plethysmography), splanchnic blood flow (indocyanine green dilution ), renal blood flow (p-aminohippurate clearance), and plasma norepinep hrine concentration. There were no significant age differences in Q(c) ; however, in both environments the O group maintained Q(c) at a highe r stroke volume and lower heart rate. At 60% VO2peak, forearm blood fl ow was significantly lower in the O subjects in each environment. Spla nchnic blood flow fell (by 12-14% in both groups) at the lower intensi ty, then decreased to a greater extent at 60% VO2peak in Y than in O s ubjects (e.g., -45 +/- 2 vs. -33 +/- 3% for the hot environment, P < 0 .01). Renal blood flow was lower at rest in the O group, remained rela tively constant at 35% VO2peak, then decreased by 20-25% in both group s at 60% VO2peak At 60% VO2peak, 27 and 37% more total blood flow was redistributed away from these two circulations in the Y than in the O group at 22 and 36 degrees, respectively. It was concluded that the gr eater increase in skin blood flow in Y subjects is partially supported by a greater redistribution of blood flow away from splanchnic and re nal vascular leeds.