Decreased pulmonary pressor response to acute hypoxia in chronically hypoxic rats

The pulmonary vascular response to an acute hypoxic stimulus was examined in rats which were kept for 4 weeks in a hypoxic environment and compared to that of rats kept in a normoxic environment. To this end, the effects of breathing gas mixtures containing 7, 21 an 100% O2 on right ventricular systolic pressure (RVPs), cardiac output (Q) and calculated pulmonary vascular resistance (PVR) in chronically hypoxic (CH) rats and rats kept in a normoxic environment (N) were examined. During breathing of 21% O2 RVPs, Q, and PVR were all higher in CH than in N rats. Breathing a gas mixture containing 7% O2 had no effect on systemic blood pressure, heart rate or Q, in both CH and N rats. When compared to breathing of 21% O2, the RVP and PVR remained unchanged in CH rats breathing 7% O2, while both variables significantly (p less than 0.01) increased in N rats. The presented data indicate that the reaction of the pulmonary vasculature to an hypoxic challenge is decreased in CH rats.