Pulmonary diffusing capacity in man during immersion in water

Abstract

During immersion in water to the neck, 7 seated resting normal subjects showed, without exception in 14 trials, an increase in diffusing capacity of the lung (DLco) which averaged 16.2 [plus or minus] 0.79 SD % of the control (unimmersed) values (P < 0.001). At an intermediate depth of immersion at which the calculated hydrostatic pressure (gauge) was approximately halved, the rise in DLCO was also halved. The hemo-dynamic readjustment to external pressure was completed within a few minutes, since no further change in DLCO occurred during continuous immersion to the neck for as long as 90 min. Immersion produced a rise in "permeability" of the lung (KCO) which was on the average 5.8% greater than that in DLcO. In 3 subjects the pulmonary capillary capillary blood volume (Vc) rose on the average 47% at the deeper level of immersion, suggesting that, as in the pressure suit, the rise in DLCO was due to pulmonary vascular engorgement.