Studies In Vitro and in Canine Mesenteric Vessels

The accuracy and reliability of a noninvasive pressure- sensitive capsule for the endoscopic measurement of esophageal varix pressure was evaluated. Capsule pressure was correlated with direct intraluminal pressure measurements. The influence o/vessel wall tension on capsule pressure was also assessed. In vitro studies demonstrated an excellent correlation (r ≥ 0.94; p < 0.001) between the pre~sure obtained with the capsule and intraluminal pressure over a range of vessel diameters and wall thicknesses. In vivo correlation of pressures obtained with the capsule with direct venous pressure measurements was excellent (r = 0.85). However, this correlation decreased with a decrease in vessel diameter (group 1 diameter ≥ 10 mm, r = 0.95; group 2 diameter ≥ 5 mm but < 10 mm, r = 0.75; group 3 diameter ≥ 3 mm but < 5 mm, r = 0.81). This decrease in accuracy was significant (p < 0.001) between group 1 and groups 2 and 3. In vitro and in vivo, capsule pressure variability was significantly greater (p < 0.001) in vessels of smaller diameter. Wall tension significantly influenced capsule pressure (p < 0.05), although this effect was only seen in large “vessels” with a diameter beyond a clinically relevant range. Therefore, despite obtaining technically acceptable capsule pressure measurements in ideal experimental conditions, the accuracy and variability of these measurements are limited by vessel size.