DISTENSIBILITY OF SMALL PULMONARY BLOOD-VESSELS

Although vasomotor activity in small pulmonary vessels has been studie d extensively in the past, using the concept of resistance to flow, in formation on the distensibility of these vessels is very sparse. In an attempt to reduce this deficit, we adapted a theoretical method devel oped for small systemic vessels, to estimate distensibility of pulmona ry resistance vessels in experimental animals and man. Pressure-flow d ata from 11 dogs and 10 human subjects (5 control subjects and 5 patie nts with long-standing left heart failure) were used to calculate dist ensibility of small pulmonary vessels. The conductance, G, was calcula ted from these data as the ratio of blood flow to driving pressure. Th e slope of the relationship between the logarithm of G1/4 and the aver age distending pressure (ADP) provides a graphic picture of circumfere ntial extensibility, E, defined as percent change in radius for an inf initesimal change in ADP. Results indicate that: (1) the value of E in dogs was 1.85 +/- .40 mmHg-1 for the control state, which decreased t o 1.45 +/- .43 mmHg-1 during norepinephrine administration; however, t he decrease in the value was not statistically significant (p = 0.53); (2) the value of E in control human subjects was 3.38 +/- .47 mmHg-1 and the value of E in patients with left heart failure was -0.64 +/- 0 .39 mmHg-1; the difference was significant (P = .0001). Moreover, at a given ADP in the range of overlapping pressures, the ''average'' radi us of small pulmonary vessels in patients with left heart failure was smaller than that in the control subjects; and (3) small pulmonary ves sels were more distensible than both the small systemic vessels and th e large pulmonary arteries.