Does increased pulmonary blood flow redistribute towards edematous lung units?

Unilobar pulmonary edema secondary to increased capillary permeability was produced utilizing oleic acid infusion into the left lower lobe pulmonary artery of seven dogs. This model was used to determine whether random changes in cardiac output produced by opening and closing arteriovenous fistulae were associated with changes in fractional perfusion to the edematous lobe (as determined by differentially labeled radiomicrospheres) thus explaining changes in intrapulmonary shunt. With an increase in cardiac output from a mean (+/- SD) of 1.6 +/- 0.5 liters/min to 2.6 +/- 0.8 liters/min (P less than 0.01), mean (+/- SD) injured lobar shunt as measured from O2 contents of lower lobar pulmonary venous blood and mixed venous blood increased from 54.4 +/- 3.0% to 74.4 +/- 22.1% while total intrapulmonary shunt increased from 12.0 +/- 4.0% to 16.0 +/- 3.7% (P less than 0.01). This increase in intrapulmonary shunt was, however, not associated with preferential perfusion of the edematous lobe, the mean (+/- SD) of the perfusion to the edematous lobe expressed as a percentage of the cardiac output being 16.6 +/- 1.6% at the low cardiac output and 16.9 +/- 1.4% at the high cardiac output. It is concluded that redistribution of blood flow towards the edematous lobe does not occur with increases in cardiac output and therefore does not account for the increased intrapulmonary shunt.