Lack of effect of acute hypoxia and hypercapnia on muscle relaxation rate in man.

The effect of acute hypoxia and hypercapnia on skeletal muscle relaxation rate was investigated in man. The contractile force of limb muscles (quadriceps femoris and adductor pollicis) was studied in normal subjects using electrical stimulation. The twitch transdiaphragmatic pressure was used to investigate the diaphragm. The maximum relaxation rate was measured from contractions of the non-fatigued quadriceps femoris, adductor pollicis and diaphragm. Severe hypoxia (mean transcutaneous oxygen tension 40 mmHg) did not alter the maximum relaxation rate from 20 Hz stimulated contractions of the non-fatigued quadriceps. Acute hypercapnia (mean end-tidal CO2 tension 65.1 mmHg) did not significantly change the maximum relaxation rate from 20 and 100 Hz tetanic contractions of non-fatigued quadriceps. The maximum relaxation rate from 1 Hz twitch tension and 20 Hz tetanic tension of adductor pollicis was also not altered by acute hypercapnia (mean end-tidal carbon dioxide tension 63 and 60 mmHg, respectively). The maximum relaxation rate from twitch transdiaphragmatic pressure was not altered by acute hypercapnia (mean end-tidal carbon dioxide tension 69.7 mmHg).