TRANSFER OF CARBON-MONOXIDE DURING AN INSPIRATORY PAUSE PROCEDURE IN MECHANICALLY VENTILATED PIGS

We studied the effect of forced inflation at different alveolar volume s (V-A) on carbon monoxide diffusing capacity (DL(CO)) in anaesthetize d, paralysed and mechanically ventilated healthy pigs. An inspiratory pause procedure (equivalent of the single-breath technique) consisting of a pause between an inflation and expiration, both at a constant fl ow rate, was used. The procedure was computer-controlled and could eas ily be standardized. In five pigs, V-A was varied at constant inflatio n volume by increasing positive end-expiratory pressure (PEEP) from 2 to 10 cmH(2)O. Inspiratory pause time was varied from 1 to 8 s to veri fy whether the decay of CO was exponential. In nine pigs, DLCO was est imated at four different V-A values by inflating with 15-30 mi kg(-1) at 2 cmH(2)O PEEP. An exponential decay of CO was always obtained, Wit h increasing V-A by either an increase in PEEP or inflation volume, DL CO remained constant. Since the diffusing capacity of the pulmonary me mbrane is expected to increase with increasing V-A, the constant DL(CO ) may be attributed to a decrease in capillary blood volume.