The purpose of this study was to measure the magnitude of the hypoxic pulmonary vasoconstriction(HPV) response to hypoxia of left lung and the effect of positive end-expira pressure(PEEP) of right lung on the regional HPV of left lung.

Left thoracotomy was performed in eight female mongrel dogs. Left pulmonary blood flow(Q) was measured with electromagnetic blood flow probe and cardiac output with tliermodilution technique in triplicate. Systemic and pulmonary hemodynamics were measured via Swan-Ganz and indwelling catheters. Q was shown as percent of cardiac output(Q%). Total, right and left pulmonary v.ascular resistance(PVRt, PVRr and PVR1) and pulmonary shunt(Qg/Qt) were calculated. Through the study, the right lung was ventilated continuously with 100% O2, while the left lung was either ventilated with 100% O2(control: phased 1)and a gas mixture containing 4% O2, 3% CO2 and 93% N2 (hypoxic: phase2I and 3). In phase 3 10 cmH2O PEET was applied to the light lung.

Left lung hypoxia in phase 2 results in a reduction of Ql% and PaO2 and a elevation of PVRl without any changes of PVRt, Qs/Qt, MPAP and pulmonary perfusion pressure(PPP). With a 10 cm H2O PEEP on the light lung in phase 3, Ql% returned to the control level, but PVRl was still higher as compared to control . PaO2 and Qs/Qt were further aggravated. PVRt and PVRr were elevated in phase 3 as compared to phase 1and 2.

It is concluded that contra-lateral PEET during unilateral HPV may aggravate systemic hypoxemia via blood flow diversion away from the PEETed area to the hypoxic area, but not abolish hypoxic pressor respone of hypoxic area.