Increased pulmonary venous resistance contributes to increased pulmonary artery diastolic-pulmonary wedge pressure gradient in acute respiratory distress syndrome

Background: Pulmonary artery diastolic (PAD)-pulmonary wedge pressure (PWP) gradient has been shown to be increased in sepsis and acute respiratory distress syndrome (ARDS). Because pulmonary venous vasoconstriction induced by endotoxentia in sepsis or postcapillary leukocyte aggregation in ARDS or both can increase pulmonary venous resistance (Rpv), it is possible that the elevated Rpv increases PAD-PWP. The authors examined this possibility by assessing the correlation between Rpv and PAD-PWP gradient in patients with ARDS. Methods: Included were 20 patients with ARDS who required surgical procedures during general anesthesia. Rpv was calculated as the difference between mean pulmonary artery (PA) output pressure and PWP divided by cardiac index. Mean PA output pressure was computed from harmonic form of the recorded PA pressure by applying an attenuating factor to its phasic components, for which Fourier analysis was used. Total pulmonary vascular resistance (TPVR) was calculated as the difference between mean PA input pressure and PWP divided by cardiac index. To avoid the effect of PA resistance on TPVR and Rpv, the relative pulmonary venous resistance (Rpv/TPVR) was used. Results: There was a good correlation between Rpv/TPVR and PAD-PWP gradient (R-2 = 0.698, P < 0.0001). When patients were classified into two groups based on PAD-PWP gradient, the Rpv/TPVR was 0.66 +/- 0.06 in the group with a PAD-PWP gradient of 6 mmHg or greater and 0.46 +/- 0.08 in the other group (P < 0.0001). Conclusion: A strong correlation between Rpv/TPVR and PAD-PWP gradient suggests that the increased Rpv contributes to increased PAD-PWP gradient in patients with ARDS.