Effect of alteration of pheripheral blood flow on the central circulation in man during supine cycling in different ambient temperatures.

Whether the alteration of peripheral circulation caused by changing ambient temperature (Ta) affects central circulatory changes in man during supine cycling was investigated in four well-trained men, who exercised at two levels (117.7 or 176.6 W). Exercise metabolic rate (VO2) in cold (0 degree C or 10 degrees C) was the same as it was at 20 degrees C, whereas the cardiac output (CO; CO2 rebreathing technique) and heart rate were significantly lower (e.g.,176.6 W at 0 degree C, both p < 0.01). In heat (30 degrees C or 40 degrees C), the VO2 reduced with falling CO and mean arterial blood pressure from those at 20 degrees C (e.g., 176.6 W at 40 degrees C, all cases p < 0.01), whereas the peak post-exercise calf blood (CBFp) increased (p < 0.01). The VO2 and stroke volume (SV) were inversely proportional to the ratio of CBFp to CO/kg body weight (CBFp/CO) (r > -0.78, p < 0.001). Total peripheral resistance (TPR) was related to arteriovenous oxygen difference (A-VO2 difference) (r > 0.78, p < 0.001). The TPR and A-VO2 difference decreased as Ta rose, while CBFp/CO was almost the same. As CBFp/CO had exceeded 50 and further progressed, however, the two parameters elevated until the same level as that at 0 degree C. The present results suggest that during moderately prolonged (16--60 min) supine cycling in different Ta's the central circulatory changes are mainly affected by the altered peripheral blood flow in competing between skin and muscle for blood flow.