Increased Pulmonary Venous Resistance in Morbidly Obese Patients without Daytime Hypoxia

Abstract

Background The pulmonary artery (PA) diastolic-pulmonary capillary wedge pressure (PAD-PCWP) gradient has been shown to be increased in morbidly obese patients without daytime hypoxia. In sepsis, the increased pulmonary venous resistance (PvR) contributes to increases in PAD-PCWP gradient. In addition, the obesity-related endotoxemia is known to be involved in the pathophysiology of metabolic syndrome in obesity. Therefore, it is possible that the increased PvR contributes to increases in PAD-PCWP gradient in morbid obesity. We examined this possibility. Methods Included were 25 obese patients without daytime hypoxia undergoing bariatric surgery under general anesthesia. PvR was calculated as the difference between mean PA output pressure and PCWP divided by cardiac index. Mean PA output pressure was computed from the 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 pressure and PCWP divided by cardiac index. To avoid the effect of PA resistance on TPVR and PvR, the PvR/TPVR ratio was used. Results There was a good correlation between PvR/TPVR ratio and PAD-PCWP gradient (r2=0.785, P<0.0001). When patients were divided into two groups based on PAD-PCWP gradient, the PvR/TPVR ratio was 0.67+/-0.06 (mean+/-SD) in the group with a PAD-PCWP gradient of at least 6 mmHg and 0.48+/-0.05 in the other group (P<0.0001). Conclusions A strong correlation between PvR/TPVR ratio and PAD-PCWP gradient suggests that the increased PvR contributes to increased PAD-PCWP gradient in obese patients without daytime hypoxia.