抄録
It has been thought that a mechanoreflex from exercising muscles as well as central command descending from higher brain centers plays an important role in cardiovascular adaptation during dynamic exercise. To examine a contribution of the muscle mechanoreflex to the cardiovascular adaptation during dynamic exercise, we measured the responses in heart rate (HR), stroke volume (SV), cardiac output (CO), arterial pressure (AP), and total peripheral resistance (TPR) during passive cycling in 8 subjects. AP was continuously measured with a Finometer device. Beat-to-beat changes in SV, CO, and TPR were calculated using Modelflow®. SV and CO increased and TPR decreased during passive cycling with ergometer, whereas HR slightly increased only at the initial period of passive cycling. Because electromyogram of the leg muscles did not appear during passive movement, active contraction was excluded. To eliminate the effect of venous return on the increase in SV, we performed the passive cycling either with or without venous occlusion of the legs (bilateral thigh cuffs inflated to 100 mmHg). Venous occlusion reduced the increase in SV and thereby attenuated the increase in CO during passive cycling. These data suggests that the increases in SV and CO during passive dynamic exercise are chiefly mediated by increased venous return but not by a muscle mechanoreflex. In conclusion, a muscle mechanoreflex may play a minor role in the cardiovascular adaptation during dynamic exercise with a lower intensity. [J Physiol Sci. 2007;57 Suppl:S200]
