Lung tissue volume during development of edema in isolated canine lungs

The technique of estimating pulmonary tissue volume (Vt) by rebreathing a tissue-soluble gas is rapid and noninvasive. We examined the sensitivity of this technique for the estimation of Vt in isolated, perfused canine lungs during the development of pulmonary edema. Vt was 84 +/- 15% (mean +/- SD) of the associated lung weight for lung weights of up to 240% of base line but decreased to 70 +/- 2% when lung weight exceeded 310% of base line. Small rebreathing tidal volumes resulted in significantly smaller values for Vt in edematous lungs. An abrupt increase in pulmonary venous pressure increased lung weight due to vascular distension; Vt measurements detected less than half of this increase, implying that certain portions of the intravascular blood volume are not measured by this technique.