Reversible temperature-sensitive alterations in lung fluid balance

Hypothermia is intentionally imposed during the harvesting of lungs for tra nsplantation. The aim of this study was to investigate the fluid balance al terations in rat lung preparations exposed to hypothermic perfusion. Loweri ng perfusate temperature from 37 degreesC to values between 27 and 7 degree sC caused an immediate, marked pulmonary hypertension and vasoconstriction accompanied by rapid development of pulmonary edema (+1.15 g, or similar to 90%, gain in lung weight within 5 min). However, on rewarming, vasoconstri ction was immediately reversed. Edema was resolved, but along a two-compone nt time course: an immediate reduction of lung weight on rewarming (t(1/2) of 0.5 min) that mirrored the recovery of pulmonary artery pressure and vas oconstriction, and also a slower pressure-independent component of recovery (t(1/2) of 3.5 min). Ouabain (300 muM) markedly inhibited the lung's abili ty to recover from edema, indicating that fluid clearance from lung tissue was the result of activation of ouabain-sensitive (Na+,K+)-ATPase pump. Res ults could not be explained by vascular or airspace injury as lung sections from hypothermic lungs appeared normal. The findings indicate that hypothe rmia induces pulmonary edema formation, which can be rapidly cleared upon r ewarming by activation of ouabain -sensitive (Na+,K+)-ATPase pump. Thus, im paired fluid clearance from lung extravascular spaces may be a critical fac tor limiting gas exchange in transplanted lungs exposed to hypothermia.