EFFECTS OF POSTURE ON BLOOD-FLOW DIVERSION BY HYPOXIC PULMONARY VASOCONSTRICTION IN DOGS

We used differential excretion of sulphur hexafluoride from the left a nd right lung to measure blood flow diversion by hypoxic pulmonary vas oconstriction (HPV) in the prone and supine positions in dogs (n=9). G as exchange was assessed using the multiple inert gas elimination tech nique. Blood flow diversion from the hypoxic (3% oxygen) left lung was mean 70.7 (SD 11.2)% in the supine compared with 57.0 (12.1) % in the prone position (P<0.02). The supine position was associated with incr eased perfusion to low (V) over dot (A)/(Q) over dot regions (P<0.05). The increased flow diversion with hypoxia in the supine position was associated with more ventilation to high (V) over dot (A)/(Q) over dot regions (P<0.05). We conclude that flow diversion by hypoxic pulmonar y vasoconstriction is greater in the supine position. This effect coul d contribute to the variable response in gas exchange with positioning in patients with ARDS.