MAGNITUDE AND TIME-COURSE OF ACUTE HYPOXIC PULMONARY VASOCONSTRICTION IN MAN

Acute hypoxic pulmonary vasoconstriction has an established role in the preservation of ventilation-perfusion balance. To further characterize this homeostatic response in man we have attempted to measure both the time course and magnitude of blood flow diversion from single hypoxic lobes. Lobar hypoxia (mean P-O2 38 +/- 1.5(SEM)mmHg, mean P-CO2 39.9 +/- 0.9 mmHg) was induced by inflating catheter-tip balloons in left upper lobe bronchi during fibreoptic bronchoscopy under local anaesthesia in 8 normal subjects. An index of lobar blood flow was obtained by acquiring dynamic scintigraphic lung images during a continuous intravenous infusion of the short-lived radioisotope krypton-81m dissolved in 5% glucose solution. In 3 subjects blood flow to the occluded lobes was monitored while the lobes were maintained under hyperoxic conditions (mean P-O2 127.8 +/- 31.5 mmHg, mean P-CO2 40.2 +/- 1.3 mmHg). Under hypoxic conditions the blood flow to the occluded lobes fell to 53% of baseline after 5 min with a mean time constant of 151 +/- 24.8 sec. Under hyperoxic conditions there was no significant change from baseline blood flow. We conclude that this technique has allowed us to monitor both the dynamic and steady state responses of the pulmonary circulation to lobar hypoxia in man.