We studied the effect of incremental infusion of fluid volume in a tamponade balloon on intraluminal pressure and uterine blood flow. Following placental delivery, a tamponade balloon was inserted into the uterus and incrementally inflated. Intraluminal pressure was measured at incremental volumes. Ultrasound was used to determine positioning of the catheter, uterine wall thickness, and uterine artery velocity waveforms in eight patients. Pressure-volume relationship was estimated by regression analysis. Significance was p < 0.05. There was a significant exponential curvilinear relationship between balloon pressure and infused volume at the maximum volume for each subject ( R = 0.64, p = 0.01). Doppler ultrasound showed that at or above 1000 mL inflation volume, 5/6 patients (83%) showed reversal of uterine artery diastolic flow. At maximal inflation volume, all of the patients with reversed diastolic flow had intraluminal pressure less than systolic blood pressure. Intraluminal pressure increases curvilinearly as volume of an intrauterine tamponade balloon is increased. The mechanism of action of tamponade balloons is likely related to a reduction in uterine artery perfusion pressure. Whether this is the result of direct compression of the artery in the lower segment or due to wall conformational changes is not clear.
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