[The influence of lung volume and body position on pulmonary blood flow under hypoxic exposure]

We examined the changes in the electromagnetically measured left lower lobe blood flow (QLLL) when the left lower lobe (LLL) was exposed to alveolar hypoxia selectively under two different positions (supine and right lateral position in 18 dogs. QLLL/CO, Qs/Qt and other cardiopulmonary parameters were obtained during the following experimental sequence; 1) the whole lung ventilated with 100% O2 (control), 2) LLL collapsed and the remainder ventilated with 100% O2, 3) N2 expansion of LLL (N2 CPAP) and the remainder ventilated with 100% O2, 4) O2 expansion of LLL (O2 CPAP) and the remainder ventilated with 100% O2, and 5) The whole lung ventilated with 100% O2. In the supine position group (n = 9), both selective collapse and N2 CPAP of LLL caused QLLL/CO to decrease significantly (P less than 0.02) from control values (14.9 +/- 1.7%) to 10.6 +/- 0.9% and 11.9 +/- 1.6%, respectively. But there was no difference in QLLL/CO between collapse and N2 CPAP of LLL. In the right lateral position group (n = 9), hypoxic exposure of LLL caused no decrease in QLLL/CO from control values. But QLLL/CO during N2 CPAP (8.5 +/- 1.1%) decreased significantly than that during collapse (10.8 +/- 1.5%) (P less than 0.02). Qs/Qt during N2 CPAP (15.6 +/- 1.4%) also decreased significantly (P less than 0.05) from that during collapse (18.5 +/- 2.2%). We conclude that the difference of the changes in QLLL/CO under hypoxic exposure between supine and right lateral position was caused by hydrostatic pressure which influenced more during lateral position than during supine position.