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

Summary Whether the alteration of peripheral circulation caused by changing ambient temperature (T_a) 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 C or 10 C) was the same as it was at 20 C, whereas the cardiac output (CO; CO₂ rebreathing technique) and heart rate were significantly lower (e.g., 176.6 W at 0 C, both p<0.01). In heat (30 C or 40 C), the VO₂ reduced with falling CO and mean arterial blood pressure from those at 20 C (e.g., 176.6 W at 40 C, all cases p<0.01), whereas the peak post-exercise calf blood flow (CBF_p) increased (p<0.01). The VO₂ and stroke volume (SV) were inversely proportional to the ratio of CBF_p to CO/kg body weight (CBF_p/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 T_a rose, while CBF_p/CO was almost the same. As CBF_p/CO had exceeded 50 and further progressed, however, the two parameters elevated until the same level as that at 0 C. The present results suggest that during moderately prolonged (16–60 min) supine cycling in different T_a's the central circulatory changes are mainly affected by the altered peripheral blood flow in competing between skin and muscle for blood flow.