[Physiological mechanisms limiting external respiratory resistance].

A study was performed on 8 healthy male subjects to investigate the effect of nonelastic resistance 6-40 GPa (the air flow velocity being 90 l/min) on the duration of proprioceptive reflexes of respiratory muscles, volume and velocity parameters of forced exhalation. Resistances of 15 and 25 GPa combined with a workload of 100-150 W increased the duration of proprioceptive reflexes from 0.18 +/- 0.015 to 0.29 +/- 0.012 sec and to 0.38 +/- 0.06 sec, respectively, which indicates fatigue of respiratory muscles. Resistance of 25 GPa reduced significantly (by 55%) the maximum volume velocity of forced exhalation and increased its duration by 31%, the exhalation volume decreasing insignificantly (by 6%). The major factor limiting man's tolerance to external respiration resistance is functional deficiency of proprioceptive regulation of respiration and strength and velocity of respiratory muscles.