Potentiation of Lobar Hypoxic Pulmonary Vasoconstriction by Intermittent Hypoxia in Dogs

Based on previous whole lung findings, the authors tested the hypothesis that lobar hypoxic pulmonary vasoconstriction (HPV) would be potentiated by repeated intermittent lobar hypoxic challenges. In sixteen open-chested pentobarbital-anesthetized dogs they found that repetitive selective hypoxia of the left lower lobe (LLL) (Group I = LLL nitrogen ventilation, n = 8; Group II = LLL absorption atelectasis, n = 8) caused the percentage decrease in the electromagnetically measured fraction of the cardiac output perfusing the LLL (&OV0422;LLL/&OV0422;1) to become progressively greater (increased LLL HPV) through the first three hypoxic challenges in Group I and through the first four hypoxic challenges in Group II. In four dogs in each group, after eight sequential hypoxic challenges with the initial standard method had been performed, the alternative method was performed three times. There was no significant difference between the eighth LLL HPV response and the subsequent three. These findings indicate that 1) the mechanism of blood flow decrease to atelectatic lung is probably the same as for nitrogen-ventilated lung, namely, by HPV, and 2) in order to maximize HPV in the nonventilated lung during one lung ventilation, several repeated intermittant cycles of deflation-inflation to the lung should be performed during the initiation of one lung ventilation.