Method for detection of intracellular pH threshold; comparison between subjective observation and regression analysis.

Abstract

The aim of this study is to examine the objectivity and reproducibility of intracellular pH threshold (pHT) detected by eye (E), and by regression analysis on linear (L), semilog (SL) and log-log (LL) models. Threshold for inorganic phosphate-to-phosphocreatine ratio (PT) was also examined by three regression analysis. Fifteen males volunteered as subjects. They performed wrist flexion in a ramp protocol of 0.14W/min till exhaustion. Throughout the exercise, 31P-MRS was obtained continuously from wrist flexors. Intracellular pH and phosphate compound in the muscle tissue were monitored as minute-by-minute data. In E, three observers determined pHT subjectively as a work rate just before pH decrement. In three regression analysis, pHT was detected as an intersection of a pair of linear regression lines which was selected statistically or subjectively. pHT detected by four methods showed significant reproducibility between each other, although PT did not. These results provide one of the evidences of threshold behavior of change in pH, and a question of existence of PT in contrast to pHT.