Effects of hyperphosphatemia on diaphragmatic strength and endurance

Effects of an infusion of Na₂HPO₄ on diaphragm strength, endurance, and magnitude of recovery were evaluated in in situ canine diaphragm strips. Results showed no effect on maximal isometric tetanic tension. Twitch tension and tension in the low- (10-Hz) frequency range were significantly increased (P < 0.01). Time to fatigue (endurance) increased by 38 ± 4.5% in the group that received phosphorus compared with its control and decreased by 18.5 ± 2.5% in the group that received dextrose compared with its control (P < 0.005). Recovery from fatigue was also significantly improved after the phosphorus infusion. Serum ATP and 2,3-diphosphoglycerate levels were unchanged throughout the experiment. The results of this study support the notion that hyperphosphatemia improves diaphragmatic endurance and recovery from fatigue. The mechanisms involved may in part be due to the phosphate- buffering effects, which limit the extent of the muscle intracellular acidosis produced with fatigue.