Distribution of ventilation-perfusion ratios in pneumonectomized dogs

In this paper, the distribution of ventilation (VA) and of pulmonary perfusion (Q), gas exchanges, and the single breath CO diffusing capacity are measured in 8 dogs before and after left pneumonectomy. During surgery 4 dogs, in which the left pulmonary artery is clamped, and 4 other dogs in which the left mainstem bronchus is clamped, are studied. A minute ventilation (VE) is adjusted during the initial stage in each dog but it is kept constant for the other stages. For the entire group of dogs, the overall VE/Q varies from 0.8 to 3.0 in the baseline study. In the initial study, the perfusion distribution is unimodal and the ventilation distribution is unimodal or bimodal. The percentage of ventilation of the second mode correlates approximately with the overall VA/Q. After clamping the left pulmonary artery, the correlation between overall VA/Q, capillary shunt, and blood gases data is excellent and the ventilation and perfusion distributions are both bimodal. One perfusion mode is situated in the low VA/Q ratios while one ventilation mode is situated in the high VA/Q ratios. After clamping the left mainstem bronchus, the average anatomical shunt is 27%, the ventilation and perfusion are both bimodal, and the mean PaO2 is 55 mm Hg. Ultimately the ventilation and perfusion distributions tend to return to normal after pneumonectomy.