Effect of restricted blood flow on intracellular pH threshold of working muscle

Threshold of decline in intracellular pH of muscle (pHT) during incremental wrist flexion was studied by 31P-MRS, under two levels of occlusions in which the cuff of the upper arm was inflated to systolic (ES) and diastolic blood pressure (ED), and no occlusion (E). To observe the effect of occlusion per se, intracellular pH at rest under the same two levels of occlusion was measured. Additionally, NIRS was applied to monitor the oxygenation and blood volume of the tissue during the same experimental protocol as the 31P-MRS study. Ten healthy Japanese males participated as subjects in the 31P-MRS study, and three of them in the NIRS study. They performed wrist flexion in incremental loads of 0.14 W/min ramp until voluntary exhaustion. 31P-MRS and NIRS were obtained from wrist flexor muscles. Change in intracellular pH (pH) during wrist flexion showed a threshold behavior even in ischemic conditions, although pH did not decrease at rest under the same two levels of occlusion. This finding indicated that decrease in pH under occlusion is also resulted from exercise induced lactic acidosis. Obtained pHT in ES was smaller than in ED and E significantly, and there was no significant difference between pHT in ED and that in E. From the results of NIRS study, it was confirmed that only venous outflow but not arterial inflow was restricted under an occlusion at a pressure of diastolic blood pressure, but both under an occlusion at a pressure of systolic blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)