INTRAPULMONARY GAS MIXING AND PULMONARY GAS-EXCHANGE IN ARTIFICIALLY VENTILATED DOGS

To investigate the effect of incomplete gas mixing between tidal air a nd residual gas on pulmonary gas exchange, anaesthetized dogs were ven tilated artificially with breathing patterns with different durations of the post-inspiratory apnoea (t(a) = 0, 0.5, 1.0 and 2.0 s), where t idal volume, breathing frequency, inspiratory and expiratory flow patt erns were kept constant. We determined the alveolar ventilations (V-A) of He and SF6 from the product of end-expiratory lung volume (V-L,V-E ') and specific ventilation (V-A/V-L,V-E'). V-L,V-E' was determined by the dilution technique and the specific ventilations of the two gases were obtained from their multiple-breath washout. Further, tracer amo unts of acetone, ether and enflurane were infused continuously into a peripheral vein and a bolus of a gas mixture of krypton, Freon12 and S F6 was introduced into the peritoneal cavity. We determined the Excret ion (E) and Retention (R) of these six gases according to the multiple -inert-gas-elimination technique (MIGET). V-A increased with increasin g t(a), where V-A,V-He was about 14% larger than V-A,V-SF6 For both ga ses, however, the increase in V-A relative to control (V-A for t(a) = 0) was virtually the same: 9, 11 and 19% (mean values) for t(a) = 0.5, 1.0 and 2.0 s respectively. For all dogs the E/R curve shifted to lar ger E values with increasing t(a). E for the most soluble tracer gas ( acetone) increased by 11, 21 and 25% for t(a) = 0.5, 1.0 and 2.0 s res pectively. V-A, determined with MIGET from the ventilation/perfusion d istribution, increased by almost the same percentages. These results a re interpreted to indicate that pulmonary gas exchange is substantiall y impaired by incomplete intra-acinar gas mixing.