BREATH BY BREATH MEASUREMENT OF RESPIRATORY MUSCLE GAS EXCHANGE IN CONTINUOUS MAXIMAL VENTILATION

Abstract

Respiratory muscle gas exchange as well as respiratory muscle strength has been considered to be an index of respiratory muscle performance. Oxygen consumption was measured continuously in the setting of hyperventilatory exercise.MGC 2001 and our CO2 rebreathing device for maintaining Paco2 were able to measure breath-by-breath gas exchange in sustained maximal voluntary ventilation.The time course of respiratory oxygen consumption rate yielded new knowledge, i.e. that oxygen consumption increased at the end of hyperventilation without increasing minute volume in the sitting position. On the other hand, no such phenomenon was observed in the supine position. We concluded that the supine position was most appropriates for testing respiratory muscle gas exchange.The subjects were challenged with a preparative infusion of aminophylline or placebo while in the supine position. Hyperventilation study was also performed in 11 healthy non-athletes.The results were as follows : Neither oxygen consumption nor minute volume difference significantly between the aminophylline-treated and placebo groups. However, in terms of the duration of hyperventilation (P<0.05) and the serum level of blood lactate (P<0.05) there were significant differences between the aminophylline-treated group and the control group.We concluded that aminophylline increases the endurance capacity of respiratory muscle without elevating the oxygen consumption, probably as a result of increased anaerobic metabolism.