Pressure-time product, work rate, and endurance during resistive breathing in humans.
We examined the effect of increasing work rate, without a corresponding increase in the pressure-time product, on energy cost and inspiratory muscle endurance (Tlim) in five normal subjects during inspiratory resistive breathing. Tidal volume, mean inspiratory mouth pressure, duty cycle, and hence the pressure-time product were kept constant, whereas work rate was varied by changing the frequency of breathing. There was a linear decrease in Tlim of -2.1 +/- 0.5 s.J-1.min-1 (r = 0.87 +/- 0.06) with increasing work rate. The data satisfied a model of energy balance during fatiguing runs (Monod and Scherrer. Ergonomics 8: 329-337, 1965) and were consistent with the hypothesis that the rate of energy supply, or respiratory muscle blood flow, is fixed when the pressure-time product is constant. Our results indicate that during inspiratory resistive breathing against fatiguing loads, work rate determines endurance independently of the pressure-time product. On the basis of the model, our results lead to estimates of respiratory muscle blood flow and available energy stores under the conditions of our experiment.
Dodd
D S
DS
Thoracic Medicine Unit, Westmead Hospital, New South Wales, Australia.
Kelly
S
S
Collett
P W
PW
Engel
L A
LA
D000328:Adult; D004734:Energy Metabolism; D005221:Fatigue; D005260:Female; D006801:Humans; D008297:Male; D008433:Mathematics; D008954:Models, Biological; D011312:Pressure; D012119:Respiration; D012132:Respiratory Muscles / Q000502:physiology*; D013997:Time Factors