To determine whether hypoxic pulmonary vasoconstriction (HPV) occurs mainly in alveolar or extra-alveolar vessels in ferrets, we used two groups of isolated lungs perfused with autologous blood and a constant left atrial pressure (-5 Torr). In the first group, flow (Q̇) was held constant at 50, 100, and 150 ml·kg-1·min-1, and changes in pulmonary arterial pressure (Ppa) were recorded as alveolar pressure (Palv) was lowered from 25 to 0 Torr during control [inspired partial pressure of O2 (PI(O2) = 200 Torr] and hypoxic (PI(O2) = 25 Torr) conditions. From these data, pressure-flow relationships were constructed at several levels of Palv. In the control state, lung inflation did not affect the slope of the pressure-flow relationships (ΔPpa/ΔQ̇), but caused the extrapolated pressure-axis intercept (Ppa0), representing the mean backpressure to flow, to increase when Palv was ≥5 Torr. Hypoxia increased ΔPpa/ΔQ̇ and Ppa0 at all levels of Palv. In contrast to its effects under control conditions, lung inflation during hypoxia caused a progressive decrease in ΔPpa/ΔQ̇, and did not alter Ppa0 until Palv was ≥10 Torr. In the second group of experiments flow was maintained at 100 ml·kg-1·min-1, and changes in lung blood volume (LBV) were recorded as Palv was varied between 20 and 0 Torr. In the control state, inflation increased LBV over the entire range of Palv. In the hypoxic state inflation decreased LBV until Palv reached 8 Torr; at Palv 8-20 Torr, inflation increased LBV. The differences between the effects of inflation on the Ppa-Q̇ relationships and LBV in the control and hypoxic states suggest that in this preparation hypoxia caused constriction mainly in extra-alveolar vessels. Since similar previous studies in isolated pig lungs indicated that HPV occurred mainly in alveolar vessels, these results suggest that the site of HPV varies among species.
ASJC Scopus subject areas
- Physiology (medical)