Pulmonary microvascular and perivascular interstitial geometry during development of mild hydraulic edema

To study pulmonary arteriolar vasomotion in control conditions and in the transition to hydraulic edema, changes in subpleural pulmonary arteriolar diameter and perivascular interstitial volume were evaluated in anesthetized spontaneously breathing rabbits. Images of subpleural pulmonary microvessels were recorded in control conditions and for up to 180 min during a 0.5 ml.kg(-1).min(-1) intravenous saline infusion through an intact parietal pleural window. Images were digitized and analyzed with a semiautomatic procedure to determine vessel diameter and perivascular interstitial thickness from which interstitial fluid volume was derived. In control vessels, the diameter of similar to 30-, similar to 50-, and similar to 80-mum arterioles and the perivascular interstitial thickness were fairly stable. During infusion, the diameter increased maximally by 20% in similar to 30-mum vessels, was unchanged in similar to 50-mum vessels, and decreased by 25% in similar to 80-mum arterioles; the perivascular interstitial volume increased by 54% only around 30-mum microvessels. In papaverine-treated rabbits, all arterioles dilated and a larger increase in perivascular interstitial thickness was observed. The data suggest that the opposite vasomotor behavior of 30- and similar to 80-mum arterioles during development of mild edema may represent a local specific response of the pulmonary microcirculation to reduce capillary pressure in the face of an increased transendothelial fluid filtration, thus counteracting progression toward severe edema