PULMONARY VASCULAR PRESSURE PROFILE IN ADULT FERRETS - MEASUREMENTS INVIVO AND IN ISOLATED LUNGS

We have determined the vascular pressure profile in lungs of adult ferrets utilizing an anaesthetized open chested preparation and have compared the pressure profile in vivo with that in isolated, perfused lungs. Ten adult ferrets, mean body weight 980 +/- 108 g, were studied. For in vivo measurements, five ferrets were anaesthetized, mechanically ventilated and the left chest wall resected. Pressures were measured in the pulmonary artery, left atrium and by micropuncture, in 20-50-mu-m diameter subpleural arterioles and venules. During micropuncture, ventilation was stopped for 1-2 min and the lungs kept distended at an airway pressure of 6 cmH2O. Left atrial pressure was raised to approximately 8 cmH2O with saline infusion so that lungs were in Zone 3. Cardiac output was measured by thermodilution. Lungs of five other ferrets were isolated and perfused with a steady flow roller pump. In these lungs blood flow was adjusted so that pulmonary artery pressure was similar to that in anaesthetized ferrets, with airway and left atrial pressures at 6 and 8 cmH2O respectively (Zone 3). Blood haematocrit (35 +/- 7%) was similar in the two groups. In lungs of anaesthetized ferrets total arteriovenous pressure drop was 12.1 +/- 1.9 cmH2O, with cardiac output being 210 +/- 80 ml kg body weight-1 min-1. Fractional resistance in arteries was 37%, 37% in microvessels and 26% in veins. In isolated ferret lungs, though blood flow was only 48 +/- 10 ml kg body wt-1 min-1 for the same total arteriovenous pressure drop as in vivo, the longitudinal distribution of vascular resistance was similar to that in live ferrets. We conclude that in the ferret, the contribution of arteries, microvessels and veins to total vascular resistance is similar in isolated lungs and lungs in vivo.