Age alters regional distribution of blood flow during moderate-intensity exercise

During dynamic exercise in warm environments, requisite increases in skin and active muscle blood flows are supported by increasing cardiac output (Q̇(c)) and redistributing flew away from splanchnic and renal circulations. To examine the effect of age on these responses, six young (Y; 26 ± 2 yr) and six older (O; 64 ± 2 yr) men performed upright cycle exercise at 35 and 60% of peak O₂ consumption (V̇O(2 peak)) in 22 and 36°C environments. To further isolate age, the two age groups were closely matched for V̇O(2 peak), weight, surface area, and body composition. Measurements included heart rate, Q̇(c) (CO₂ rebreathing), skin blood flow (from increases in forearm blood flow (venous occlusion plethysmography), splanchnic blood flow/indocyanine green dilution), renal blood flow (p-amino-hippurate clearance), and plasma norepinephrine concentration. There were no significant age differences in Q̇(c); however, in both environments the O group maintained Q̇(c) at a higher stroke volume and lower heart rate. At 60% V̇O(2 peak), forearm blood flow was significantly lower in the O subjects in each environment. Splanchnic blood flow fell (by 12-14% in both groups) at the lower intensity, then decreased to a greater extent at 60% V̇O(2 peak) in Y than in O subjects (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 relatively constant at 35% V̇O(2 peak), then decreased by 20-25% in both groups at 60% V̇O(2 peak). At 60% V̇O(2 peak), 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°, respectively. It was concluded that the greater increase in skin blood flow in Y subjects is partially supported by a greater redistribution of blood flow away from splanchnic and renal vascular beds.