ABSTRACT

　 During onset leg cycling exercise, it has been reported that a pronounced and steep rise in right atrial pressure, stroke volume and cardiac output via activation of muscle pump are observed. An acute large increase in cardiac output may cause cerebral over-perfusion, however, its inflience on cerebral blood flow(CBF）regulation during onset exercise remains unknown. In this study, we hypothesized that a decrease in systemic vascular resistance induced by cardiopulmonary baroreceptor stimulation buffers a rapid increase in cardiac output at the onset of exercise and contributes to appropriate CBF regulation. Eleven healthy young people had increased muscle chemoreflexes （post exercise muscle ischemia, PEI condition） and no condition （control, CON condition） due to increased cuff pressure in the exercise muscles after isometric handgrip exercise （IHGex） of maximum muscle strength of 40%. Cycling exercise was performed at 20 W （60 rpm） for 1 minute with a bicycle ergometer under PEI or CON conditions. During exercise, mean arterial pressure （MAP） , cardiac output （Q）, middle cerebral artery velocity （MCA Vm） , and posterior cerebral artery velocity （PCA Vm） were continuously measured. Cycling exercise significantly increased MAP, Q, MCA Vm, and PCA Vm （steady state, P < 0.001）． However, immediately after the onset of exercise, it was observed that the MAP decreased in both conditions compared to the resting levels, while the decrease in MAP was attenuated in the PEI condition （CON vs. PEI: － 19±8 mmHg vs. － 12±5 mmHg, P = 0.021）．Similarly, significant reductions were observed in MCA Vm and PCA Vm at the onset of exercise, and these reductions were attenuated under PEI conditions （MCA Vm, PCA Vm; P= 0.026, P = 0.002）．These findings revealed that muscle pump-induced cardiopulmonary baroreceptor reflexes reduce blood pressure and thus cerebral blood flow. Therefore, it was suggested that it may have a protective effect to prevent hyper-perfusion in the cerebral circulation against an increase in Q due to an increase in central blood volume by a muscle pump immediately after the start of exercise.

DECENTE SPORTS SCIENCE Vol.43/The DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE