[Effects of different oxygen contents in inhaled mixture on development of muscle fatigue in the human inspiratory muscles].

The object of the the present study involved determining of rate of the inspiratory muscles fatigue development in healthy humans during increasing exercise under resistive loaded breathing with the air, oxygen, or hypoxic gas mixtures (FIO2 = 0.21, 1.0 and 0.13 respectively). 6 normal male subjects were studied. Volume/time parameters of breathing and parasternal integrated EMG activities were recorded under inspiratory-expiratory resistive loading 12 cm H2O/I s(-1) during increasing exercise in the air, oxygen, or hypoxic gas mixtures. The degree of inspiratory muscle fatigue was assessed by the "tension-time" index P(ml)/P(ml max) Tl/T(T) as well as by ratio of the mean amplitudes of the EMG signal spectrum in the hight-frequency (H) range to the mean spectrum amplitudes in the low-frequency (L) range (H/L). The signs of inspiratory muscle fatigue were most conspicuous during inhalation of the hypoxic mixture, compared to air. This was supported by the increased "tension-time" index, the hurried shallow breathing, and the decreased H/L ratio on 37% (p < 0.001). Only starting signs of inspiratory muscle fatigue were revealed during oxygen inhalation, although the maximum working capacity was higher than the control one (exercise in air). The results indicate that the oxygen contained in the inhaled gas mixture affects on the total working capacity total working capacity and influences the rate of inspiratory muscle fatigue development in exercising healthy men during resistive load 12 cm H2O/l s(-1). The decreased energy supply to respiratory muscles accelerates functional failure and results in fatigue, whereas the increased energy supply decelerates the development of inspiratory muscle fatigue.