Hyperventilation syndrome and muscle fatigue.

Fatigue is a frequent complaint from patients suffering from the hyperventilation syndrome. Fatigue was quantified in terms of the endurance time that a certain force can be generated in a sustained handgrip contraction, and in terms of the time course of changes in certain parameters of the EMG-power spectrum of the contracting muscles. This was done in a group of 25 normal subjects and a group of 30 patients suffering from the hyperventilation syndrome. No difference in endurance times was found. The EMG-fatiguability in the hyperventilation group developed even slower than in the normal group. In three normals the fatigue parameters were also measured in three conditions of normo-, hypo-, and hyper-capnia. No intraindividual correlations were found between fatigue parameters and CO2-levels. Neither were such correlations found between individuals in the hyperventilation group and the normal group. It is concluded that the subjective feelings of fatigue in the hyperventilation patients cannot be corroborated by the objective measurements used in this study. Thus their fatigue is not of a peripheral type. The levels of CO2 do not have an effect on objectively measured fatigue parameters. The hypothesis that lactate accumulation in contracting muscles mediates EMG-fatiguability, cannot explain the present results, and therefore is not supported by results from this study.