Alteration by hyperoxia of ventilatory dynamics during sinusoidal work

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Abstract
Hyperoxia effects on ventilatory and gas exchange dynamics were studied utilizing sinusoidal work rate forcings. Human subjects (5) exercised on 14 occasions on a cycle ergometer for 30 min with a sinusoidally varying work load. Tests were performed at 7 frequencies of work load during air or 100% O2 inspiration. From the breath-by-breath responses to these tests, dynamic characteristics were analyzed by extracting the mean level, amplitude of oscillation and phase lag for each of 6 variables with digital computer techniques. Calculation of the time constant (.tau.) of the ventilatory responses demonstrated that ventilatory kinetics were slower during hyperoxia than during normoxia (P < 0.025; average 1.56 and 1.13 min, respectively). For identical work rate fluctuations, end-tidal CO2 tension fluctuations were increased by hyperoxia. Ventilation during hyperoxia is slower to respond to variations in the level of metabolically produced CO2, presumably because hyperoxia attenuates carotid body output; arterial CO2 tension is consequently less tightly regulated.