[Effect of a Ca2+ antagonist (verapamil) on Va/Q distribution]

Effects of verapamil on pulmonary ventilation-blood flow (VA/Q) distribution were studied in ten adult mongrel dogs weighing 12.5 +/- 0.8kg (mean +/- SE) by use of the multiple-inert-gas elimination method. VA/Q distributions were almost normal during control period (mean Q = 1.22, Log SD = 0.11). Under hypoxic challenge, blood flow distribution in low VA/Q area increased (mean Q = 0.68, Log SD = 0.50), and verapamil exaggerated this VA/Q inequality (mean Q = 0.53, Log SD = 0.67). However, four dogs showed increase in PaO2 and six showed decrease in PaO2. In the group of dogs with increased PaO2, CI increased significantly (P less than 0.05). In spite of the worse VA/Q distribution, PaO2 was not always decreased by verapamil infusion. This suggests that decrease in PaO2 is prevented by increased CI. Clinically, therefore, it is necessary to observe carefully the pulmonary blood flow when verapamil is to be administered in low cardiac output cases.