EFFECTS OF VENOUS GAS MICROEMBOLI ON PULMONARY GAS TRANSFER-FUNCTION

Dynamic lung volumes and flows, slope of phase III of the single breat h oxygen test (Delta-N-2), closing volume (CV), and transfer factor fo r carbon monoxide (Tl-CO) were measured before and 1 h after an air di ve in a hyperbaric chamber to a pressure of 0.49 MPa for 40 min. Six d ivers had a bottom time of 20 min and a race of decompression of 50 kP a . min(-1),and six divers had a bottom time of 24 min and a rate of d ecompression of 100 kPa . min(-1). Decompression stops were 5 min at 0 .16 MPa and 10 min at 0.13 MPa for both groups. As control exposure th ey were breathing O-2 at atmospheric pressure for 40 min. The dive and control exposure were done on different days within 1 wk, in random o rder. Doppler ultrasound monitoring for venous gas microemboli (VGM) w as done during the first hour after the dive. VGM were detectable in a ll six divers with the fast decompression rate and in one subject with the slow rate (P < 0.01). In the subjects having VGM there was a sign ificant reduction in Tl-CO of -5.9 +/- 4.4% compared with -0.5 +/- 3.4 % after the control exposure (P = 0.034). In the five subjects without detectable VGM, the changes in Tl-CO were -2.8 +/- 3.7% and 0.2 +/- 3 .8%, respectively. There were no significant changes in dynamic lung v olumes and flows, CV, or Delta-N-2. A reduction in Tl-CO may reflect e ffects of VGM after dives in which the effect of O-2 exposure is negli gible.