Effect of body position and of respiratory frequency on distribution of pulmonary ventilation and perfusion in dogs.

Ventilation (VA) perfusion (Q) ratios distribution measured by the inert gases method is studied in 7 anesthetized dogs in supine position, in prone position at a respiratory frequency of 15 cpm, and in prone position at a respiratory frequency of 10 cpm so as to test the sensitivity of this VA/Q method. Despite the fact that the precise height-width characteristics of the distribution modes are unknown, our results show coherent changes and sensitivity of the log standard deviation of the perfusion curve, of the shunt, and of the dead space obtained with the inert gas method. After the change from supine to prone position, cardiac output increases, shunt, if it exists, diminishes, VA/Q ratios distribution becomes more uniform, and PaO2 increases and (A-a)DO2 decreases. When respiratory frequency changes from 15 to 10 cpm, cardiac output, shunt, and dead space decrease, VA/Q ratios distribution curves are slightly less homogeneous. PaO2 and PaCO2 show no significant variation. This study shows that distribution mode's characteristics can be considered as good and coherent approximations.