Journal of applied physiology
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We tested the hypothesis that decreases in alveolar O2 pressure (PAO2) of a large lung compartment would, through decreases in arterial O2 pressure (PaO2) and mixed venous O2 pressure (PVO2), result in decreases in PAO2 of the remaining small lung compartment; thus large-compartment hypoxic pulmonary vasoconstriction (HPV) would be accompanied by concomitant small-compartment HPV. In eight pentobarbital-anesthetized dogs, whose left lower lobe (LLL) inspired oxygen concentration (FIO2) was constantly 0.21, selective stepwise reductions in the rest of the lung (RL) FIO2 from 1.0 to 0.15 caused the electromagnetically measured LLL blood flow (QLLL/Qt), pulmonary vascular resistance of RL (PVRRL), and PVRLLL to increase while RL PAO2, PaO2, PVO2, and LLL PAO2 progressively decreased. ⋯ Based on previously established PAO2 levels of maximum HPV gain and LLL dose-response curves, the RL FIO2-induced changes in QLLL/QT can be explained by different rates of change in RL and LLL PAO2 and PVR. Thus, our findings indicate that if decreases in RL FIO2 cause, in turn, large decreases in PaO2, PVO2 and "normoxic" lung PAO2, then PVO2 is an important determinant of the magnitude of the HPV response.
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Comparative Study
Extrapericardial and esophageal pressures with positive end-expiratory pressure in dogs.
Using flat balloon techniques to minimize distortion and artifacts, we studied the effect of positive end-expiratory pressure (PEEP) on local surface pressures between the lung and pericardium overlying the right (R) and left (L) ventricles of ventilated closed-chest anesthetized dogs in right lateral decubitus position. To test the hypothesis that local extrapericardial [Pep(L) and Pep(R)] and average pleural pressures change equally with PEEP, we also measured esophageal pressure (Pes). When 10-cmH2O PEEP was applied, mean increases in Pes, Pep(L), and Pep(R) were 6.2, 5.6, and 5.3 cmH2O, respectively. ⋯ At each level of PEEP, volume infusion was used to increase stroke volume. Volume infusion at 20-cmH2O PEEP was associated with small 1.0- and 1.5-cmH2O increases in Pep but no change in Pes. Analysis of confidence limits showed that application of up to 20-cmH2O PEEP, with or without volume infusion to restore stroke volume, is associated with nearly equal changes in esophageal and local extrapericardial pressures.