TRANSFER OF GAS FROM THE ACINUS DURING CONTINUOUS-FLOW AND INTERMITTENT POSITIVE PRESSURE VENTILATION

We used a technique of measuring Xenon(133) washout (XeW) from the alv eolar space to evaluate transfer of gas from the acinus (Mackenzie et al., J. Appl. Physiol. 68: 2013-2018, 1990) during 2 min of apnea, 2 m in of tracheal insufflation with oxygen (TRIO) and 90 sec of intermitt ent positive pressure ventilation (IPPV) in 6 anesthetized and paralyz ed dogs. Xenon(133) dissolved in saline was injected into an occluded acinar region through a pulmonary artery catheter, and XeW was measure d by gamma scintillation scanning. With this technique, XeW during apn ea represents the contribution of cardiogenic oscillations in regional flow. The XeW rate constant (min(-1) +/- SE) was 0.37 +/- 0.03 during apnea. This was not different (P > 0.05) with TRIO (0.29 +/-0.04). Wi th IPPV, the rate constant increased to 3.49 +/- 0.39, faster than wit h either apnea or TRIO (P < 0.001). We conclude that: (1) TRIO does no t increase convective gas transfer from the acini compared to apnea; a nd (2) transfer of gas out of the acini due to cardiogenic oscillation s is a very small portion of the total gas eliminated during IPPV.