Effect of nicardipine hydrochloride on regional hypoxic pulmonary vasoconstriction

The effects of nicardipine hydrochloride on regional hypoxic pulmonary vasoconstriction (HPV) were investigated in 14 open-chest mongrel dogs. In a second group of seven dogs, HPV responses with nicardipine were assessed during constant cardiac output controlled by inflation of a balloon placed in the inferior vena cava, as higher doses of nicardipine significantly increased cardiac output. In the group with uncontrolled cardiac output, selective ventilation of the left lower lobe lung (LLL) with 100% nitrogen caused a significant decrease in blood flow to the lobe (QLLL/Qt) to 47.8 +/- 5.5% and an increase in vascular resistance of the LLL (PVRLLL) from 6018 +/- 884 to 13807 +/- 1162 dyn s cm-5. Testing hypoxic responses during infusion of nicardipine 1, 3 and 6 micrograms kg-1 min-1 showed a dose-dependent depression of HPV response. Infusions of nicardipine 3 and 6 micrograms kg-1 min-1 with LLL hypoxia resulted in a slight decrease in lobar blood flow, and a hypoxia-induced increase in PVRLLL was not statistically significant. In the controlled cardiac output group, attenuation of HPV responses by nicardipine was similar to that in the uncontrolled cardiac output group.