Nine isolated cat lungs were perfused with the animals' own blood at 37°C and ventilated by negative pressure. The diffusing capacity for CO, Dl, was measured at constant lung volume and various blood pressures and flows by a modified 10-second, breath-holding technique. In each of seven preparations in which mean intravascular pressure was raised, either by raising left atrial pressure while keeping blood flow constant, or by increasing blood flow while keeping left atrial outflow level Dl increased about 33%/10 mm Hg increase in mean intravascular pressure. In one lung, in which left atrial pressure was increased by 10 mm Hg while pulmonary artery pressure was kept constant by lowering the blood flow, Dl increased by 50%. In four preparations, in which left atrial pressure was lowered while blood flow was increased so that mean intravascular pressure remained approximately constant, there was no demonstrable increase in Dl. We conclude that the pressure across the walls of the pulmonary blood vessels is a primary factor in controlling the size of the pulmonary capillary bed as measured by Dl. No independent effect of flow was observed. Submitted on September 9, 1959
Critical closing pressures were measured as an index of vasomotor tone in the legs of eight rabbits. In seven of these increases in the venous pressure led to definite and consistent increases in critical closing pressure. In all seven preparations the response persisted when all nervous connections to the rest of the animal were destroyed. This increase in vasomotor tone in response to increased venous pressure is probably due to a local veno-vasomotor reflex.
Simultaneous outflow and inflow rates with a constant driving pressure but varying hydrostatic (venous outflow) pressure were measured in 37 isolated ears perfused with Ringer-Locke solution. Flow increased as the hydrostatic pressure was raised (due to passive distension of the vessels) but in six cases there was a decrease in both inflow and outflow at the highest hydrostatic pressures. As hydrostatic pressure was raised outflow fell below inflow, indicating increased capillary filtration, and this complicated the interpretation. It was concluded that in less than half the cases there may have been a ‘veno-vasomotor reflex’ to raised venous pressure. Evidence of the reflex was definite in six (15%) of the cases. The results cannot distinguish between a ‘reflex’ or a possible ‘myogenic effect,’ but do show that it can occur without central nervous connections.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.