Several medical conditions involving a range of organ systems have been linked to ischemia, and chronic pelvic ischemia has been associated with lower urinary tract systems, including detrusor overactivity and detrusor underactivity [1]. Acute bladder ischemia has not been studied to the same extent as chronic ischemia, resulting in a knowledge gap.  Acute bladder ischemia is important in situations such as acute urinary retention, which may produce both detrusor overactivity and underactivity in a rat model with effects that remained after retention release [2]. The bladder is assumed to have collateral circulation and occlusion of one superior vesical artery is not expected to lead to significant pathology. For example, the creation of a Boari flap may involve the sacrifice of the contralateral vascular pedicle, and depends on sufficient collateral circulation for the preservation of bladder perfusion. With little evidence on the effects of acute ischemia on bladder function, the division of the pedicle may affect bladder function more than anticipated. To address the limited understanding of collateral bladder blood flow, the aim of the present study was to test the hypothesis that pig bladders are composed of two hemispheres that are primarily fed by separate vesical arteries, and thus provide evidence that vascular compromise of one of the paired vesical arteries could affect the perfusion to significant regions of the bladder wall.

Bladders were harvested with their associated vasculature including the aorta, en bloc, as an intact unit from pigs immediately after slaughter at a local abattoir [3]. The vascular system was flushed with cold Krebs‐Henseleit buffer and the bladders were transported on ice to the lab for testing. Next, each pig bladder was bilaterally cannulated in the superior vesical arteries, the ureters were ligated, and the urethra was catheterized.  The bladder was placed in a warm, humidified chamber and filled through the catheter to a volume 250 mL. Then, one vesical artery was perfused with 50 mL of green dye (food coloring in water) at 10 mL/min, and then the other vesical artery was perfused with 50 mL of red dye. Photographic images were collected during each step of the perfusion dyeing process (Fig 1A) using the built-in camera on an Apple iPhone 7 that was positioned on a stationary platform above the bladder. All images were cropped to remove the background and then divided into equal halves along the midline. Chromometric analysis was performed on all images using a custom algorithm to quantify the average hue of each side of the bladder. In addition to chromometric analysis of the original images, color saturation was maximized to enhance visualization of the red and green regions (Fig 1B).

Bladders from five adult pigs were studied. Hue values were normalized yellow, because yellow is midway between green and red on the hue, saturation, brightness color wheel (Fig 2A). The average normalized hues of the green and red halves were 28⁰ ± 5⁰ and -58⁰ ± 19⁰, respectively (Fig 2). Perfusion of different colored dyes into each of the vesical arteries produced bladders with halves that demonstrated statistically different color patterns (Fig 2, n = 5, p < 0.05).

The results of this study support the hypothesis that pig bladders are composed of two hemispheres that are primarily fed by separate vesical arteries.

Chromometric analysis of porcine bladder vasculature demonstrated a lack of collateral vesical blood flow, providing evidence that the bladder might be more affected by a vascular compromise of one the vesical arteries than previously expected.  Further studies are needed to study the effects of both unilateral and bilateral acute bladder ischemia on bladder biomechanics, the mechanisms responsible for these effects, and their thresholds for reversibility.

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