PULMONARY TRANSIT-TIME AND DIFFUSION LIMITATION DURING HEAVY EXERCISEIN ATHLETES

To investigate relationships between pulmonary transit times (PTT) and pulmonary diffusion limitation during exercise, 10 high aerobic capac ity athletes (V-O2max = 5.15 +/- 0.52 1 . min(-1)) who had multiple in ert gas elimination analysis evidence suggestive of diffusion disequil ibrium were studied at rest and maximal exercise. Diffusing capacity f or oxygen (DL(O2)) was calculated from the inert gas data. First pass radionuclide angiography was performed using (99m)Technecium labeled e rythrocytes and whole lung PTT and pulmonary blood volume (PBV) were c alculated. PTT decreased from 9.32 +/- 1.41 sec at rest, to 2.91 +/- 0 .30 sec during exercise and was correlated with diffusion limitation s uggested by the inert gases (r = -0.58, P < 0.05). PBV increased durin g exercise to over 25% of whole blood volume and correlated with DL(O2 ) (r = 0.82, P < 0.01). These data suggest that diffusion limitation i s related to shortened PTT in athletes and that maximal recruitment of PBV may defend against diffusion limitation.