Effect of diltiazem on hypoxic pulmonary vasoconstriction in dogs

We have examined the effect of diltiazem upon the pulmonary vascular response to the left lower lobe (LLL) hypoxia in dogs. Without diltiazem, the fraction of cardiac output perfusing the LLL (QLLL/QT) measured by the ultrasonic doppler rheometer in the hypoxic phase was 21.0 +/- 11.7(%) of the ratio in the first normoxic phase. When diltiazem was given as a 0.48 mg/kg intravenous bolus followed by an intravenous infusion of 0.48 mg/kg/hr and 0.96 mg/kg intravenous bolus followed by an intravenous infusion of 0.96 mg/kg/hr, QLLL/QT in the hypoxic phase were 34.0 +/- 14.0, 48.6 +/- 16.1(%) of the ratio in the first normoxic phase respectively. Significant difference was observed at all diltiazem concentrations. With respect to PaO2, significant difference was not observed at all diltiazem concentrations in the ratio of the hypoxic phase to the first control phase. So we concluded that diltiazem obviously attenuated hypoxic pulmonary vasoconstriction (HPV) response but did not decrease PaO2 because of keeping myocardial oxygen balance and better ventilation/perfusing relationship.