Distensibility of small veins of the dog lung

To determine the distensibility of the intrapulmonary veins (250-2,900 μm diam) of the dog lung, we obtained X-ray angiograms from isolated lung lobes over a vascular pressure range of ~0-30 Torr. Over this pressure range the diameter vs. pressure curves tended to flatten out at the high pressures. In the pressure range of 0-19 Torr, we characterized the vessel distensibility by α (the ratio of the slope, β, of the graph of diameter vs. intravascular pressure to the intercept, D(o)). The average value of α was ~1.2%/Torr. There was a weak negative correlation (r = -0.32) between α and D(o). Infusion of enough norepinephrine to produce ~50% increase in total lobar vascular resistance produced a decrease in D(o) and α of ~33 and 32%, respectively.