Effect of heart rate and stroke volume on gas mixing in dog lung

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Abstract
In 9 anesthetized and ventilated dogs heart block was induced at thoracotomy, a pacemaker was inserted, and an electromagnetic flow transducer was placed around the main pulmonary artery. The chest was then closed. Stroke volume (SV) was varied by changing central blood volume. Ventilatory dead space (VDS) and alveolar N2 mixing efficiency (ANME) were measured at 3 levels of heart rate (HR) and 3 levels of SV independently varied during life, and also after cessation of heartbeat. Neither VDS nor ANME showed a significant change with HR or SV during life, but mean VDS increased by 43 ml (22%) and mean ANME decreased by 4.4% postmortem. Cardiac action increases gas mixing at the interface between inspired and resident gas but has only a small effect on gas mixing distal to the interface during respiration without breath holding.

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