Elasticity of small pulmonary veins in the cat

The distensibility of pulmonary veins of cats, in the diametric range of 100-1200 micrometer, was studied as a function of the venous pressure p upsilon and pleural pressure p PL, while the alveolar air pressure was maintained at zero (atmospheric). The resulting percentage changes in diameter normalized with respect to the diameter at delta P of 10 cm H20 (D10) are expressed as function of delta = p upsilon - p PL. It was found that in most cases the diameter varies linearly with delta P: D/D10 = 1 + alpha (p upsilon - p PL) where alpha is the compliance coefficient. The results show that smaller veins of the cat are more compliant than larger veins. For example, when pleural pressure is -10 cm H2O, the values of alpha for vessels in the ranges of diameters of 100-200 micrometer, 200-400 micrometer, 400-800 micrometer and 800-1200 micrometer are, respectively, 2.05, 1.44, 1.08 and 0.71 percent per cm H2O or Pa-1. The effects of lung inflation on the distensibility of pulmonary veins are also studied. Our results show that for vessel sizes in the range of 400-800 micrometer and 800-1200 micrometer the compliance constant alpha is not affected by the inflation of the lungs (changes in pleural pressure to more negative values). For smaller veins in the size ranges 100-200 micrometer and 200-400 micrometer our results show an increase in compliance from 2.05 to 2.79 and from 1.44 to 2.01 percent per cm H20 or Pa-1, respectively, when pleural pressure is changed from -10 to -15 cm H20. When the pleural pressure is more negative than -15 cm H20, however, the compliance of the vessels in the foregoing two size ranges is observed to decrease.