['Patients with cirrhosis tend to have esophageal variceal bleeding episodes at night, rather than during the day time. Since human beings carry on ordinary activities in the upright posture in the day time and are recumbent at night, we hypothesized that posture may be a factor related to a circadian variation of variceal bleeding. The aim of this study was to examine the effect of upright posture on esophageal varices hemodynamics in patients with cirrhosis.', 'Nine patients with cirrhosis and esophageal varices were included in a crossover study performed on 2 separate days. On the non-endoscopic day, cardiac output, portal vein flow velocity, and superior mesenteric artery flow velocity were measured with percutaneous Doppler ultrasonography. Plasma renin activity and plasma norepinephrine concentrations were also determined. On the endoscopic day, in addition to the above measurements, esophageal varices flow velocity was measured using transesophageal Doppler ultrasonography. These measurements were performed in the supine position and 20 min after the assumption of the upright position.', 'On the non-endoscopic day, the upright posture significantly decreased cardiac output, portal vein flow velocity, and superior mesenteric artery flow velocity. Plasma renin activity and plasma norepinephrine concentration were significantly increased after assumption of the upright position. On the endoscopic day, similar hemodynamic and hormonal changes were observed. In addition, the upright posture significantly decreased esophageal varices flow velocity. Furthermore, the magnitude of the reduction in esophageal varices flow velocity (-42%) was significantly greater than that in portal vein flow velocity (-22%, p<0.01) and that in superior mesenteric artery flow velocity (-25%, p<0.01). Although the change in esophageal varices flow velocity was not significantly correlated with that in plasma renin activity (r=-0.28) and that in plasma norepinephrine concentration (r=-0.10), it was significantly correlated with the change in superior mesenteric artery flow velocity (r=0.73, p<0.05).'] Does upright posture decrease esophageal varices flow velocity in patients with cirrhosis?