COMPONENTS OF CARBON-MONOXIDE TRANSFER AT DIFFERENT ALVEOLAR VOLUMES DURING MECHANICAL VENTILATION IN PIGS

We studied the effect of increasing alveolar volume on pulmonary carbo n monoxide transfer (DLCO) and its components, i.e. membrane diffusing capacity (D-M) and capillary blood volume (Q(c)), during mechanical v entilation in eight anaesthetized and paralysed healthy pigs (mean wei ght 11.2 kg). We used an inspiratory pause procedure for simulation of the single-breath technique, and inflated 15, 20, 25 and 30 mi kg(-1) in random order. D-M and Q(c) were derived using the Roughton-Forster equation. Per litre BTPS increase in effective V-A, DLCO (inspiratory oxygen fraction 0.30) decreased on average by 11.8 mu mol s(-1) kPa(- 1), D-M slightly increased by 2.7 mu mol s(-1) kPa(-1) and Q(c) decrea sed by 241 ml. The increase in D-M was much smaller than might be expe cted from the increase in VA, which we ascribe to a loss of the alveol ar capillary membrane for gas transfer because of the concomitant decr ease in Q(c). The decrease in ec may be explained by a squeezing effec t of the intrapulmonary pressure rise on the alveolar wall and by stre tching of lung tissue.