Dynamics of Arterial Oxygen Tension in Response to Sinusoidal Work Load in Man

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Abstract
Dynamic characteristics of the response of arterial O2 tension (Pao2) to supine submaximal leg exercise were studied in 7 physically active young men. Pao2 was recorded continuously in the radial artery at the wrist; work load was varied sinusoidally between the extremes of 250 and 1050 kpm/rnin with periods of 0.75, 1.5, 3.0, and 7.0 min. Time‐averaging harmonic analysis showed a clear dominance of the fundamental component over the second and third harmonics in the Pao2 response, indicating approximately linear properties of the underlying system within the work‐load region studied. The transfer function for PaO2, exhibiting the characteristics of a variable regulated within narrow limits in the steady‐state condition, indicated that the basic response of PaO2 to a change in work load is a transient change in the opposite direction preceded by a pure time delay. Resonance occurred for work‐load periods near 3.0 min (peak‐to‐peak deviations approaching 14 mm Hg). Referring Pao2 changes to blood entering the left heart, the estimated time delay before a change in work load resulted in a change in Pao2 amounted to 15 sec. The existence of a resonance is interpreted in terms of an unbalance between factors determining O2 uptake from, and supply to, the alveolar space.