In nine anesthetized spontaneously breathing dogs, mixed venous blood
was infused at known flows in 15 wedged areas (vascular volume about
0.7 mL) to study the pressure/flow relation and to compute the
peripheral pulmonary vascular resistance (PPVR). The pressure/flow
curves were determined during local infusion of isotonic glucose
followed by increasing concentrations of urapidil (1 nmol/L, 0.1μ
mol/L, and 10 μmol/L), mixed with the blood infusion. The
dogs breathed alternately air or a hypoxic mixture (fraction of
inspired oxygen, 10%; fraction of inspired carbon dioxide, 3%).
During normoxia or acute normocapnic hypoxia, urapidil induced no
change in PPVR. These results show that, in our preparation, at the
concentrations studied, urapidil had no effect on the peripheral
pulmonary vascular tone. Higher concentrations (1 mmol/L) would have
led to systemic hypotension.