CHANGES IN ARTERIAL AND TRANSCUTANEOUS OXYGEN AND CARBON-DIOXIDE TENSIONS DURING AND AFTER VOLUNTARY HYPERVENTILATION

The purposes of our study were (1) to investigate whether a 3-min shor t-term hyperventilation leads to posthyperventilatory hypoxemia and (2 ) to assess the role of transcutaneous blood gas measurements for moni toring oxygen and carbon dioxide changes during and after the test. In 10 male volunteers arterial and transcutaneous blood gases were measu red simultaneously before, during and after a 3-min voluntary hyperven tilation maneuver. Baseline arterial PO2 increased from 13.7 +/- 0.4 k Pa (103 +/- 3 mm Hg) to 18.6 +/- 0.3 kPa (139 +/- 2.3 mm Hg; p < 0.005 compared to baseline) during hyperventilation. After the provocation test posthyperventilatory hypoxemia occurred with a minimal mean value of 7.8 +/- 1.3 kPa (58.5 +/- 9.8 mm Hg; p < 0.05 compared to baseline ). Whereas close agreement between arterial and transcutaneous measure ments was obtained for carbon dioxide values before hyperventilation, transcutaneous O-2 consistently underestimated arterial O-2. A short-t erm over-breathing of 3 min causes a significant posthyperventilatory hypoxemia. We hypothesize that posthyperventilatory hypoxemia is cause d by hypopnea as a result of depleted CO2 body stores. Noninvasive tra nscutaneous blood gas measurements are not reliable for monitoring blo od gas changes during and after hyperventilation, most probably becaus e of the slow response time of the electrodes and the reflex vasoconst riction of the skin vessels.