Diffusing capacity and pulmonary capillary blood flow at hyperbaric pressures.

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Abstract
The pulmonary diffusing capacity (DLCO) and capillary blood flow (Qc) were calculated from the disappearance of low concentrations of carbon monoxide and acetylene from the alveolar gas during breath holding. Such measurements were performed in 5 normal subjects in a hyperbaric pressure chamber at sea level and at 3.5 and 4.8 atmospheres absolute. DLCO was found to decrease progressively with rising oxygen tension. l/DLCO increased linearly with rising mean intracapillary oxygen tension from 110 to 3,200 mm Hg (average r = 0.986). DLCO was not changed significantly by independent variation of nitrogen partial pressure from 30 to 2,400 mm Hg at constant alveolar oxygen tension. The pulmonary diffusing surface did not measurably alter with exposure to an alveolar oxygen tension of 2,400 mm Hg for 10 minutes before the measurement of DLCO. Control values at sea level of DLCO and Qc were done before and after the above studies. An average 14% decrease in DLCO was found accompaniedby a drop in Qc. These changes were thought to result from the subjects'' prolonged inactivity in the chamber during decompression rather than due to oxygen inhalation or to increased barometric pressure per se.