The mechanism by which the human bladder is able to maintain perfusion in the face of increasing distention has not been established. The following study was performed in order to characterize how progressive filling changes bladder blood flow and microcirculatory resistance in conscious patients. We also investigated the relationship between bladder compliance and overall bladder blood flow.

 

Methods:

Seventeen awake patients underwent water cystometry followed by cystoscopy under local anesthesia with intramuscular placement of a laser Doppler flow probe into the posterior wall of the bladder. Simultaneous measurements of systemic blood pressure (SBP), bladder blood flow (BBF), and intravesical pressure (Pdet.) were obtained with the bladder filled with normal saline to 0% (empty), 25%, 50%, 75%, and 100% of awake Cystometric capacity (Cmax). Additional measurements were obtained immediately post bladder drainage.

 

Results:

Mean BBF was lowest in the empty state and increased with bladder filling until its highest level occurred at 75% of Cmax. Conversely, mean bladder microcirculatory resistance (MCR; mean SBP/mean BBF) was highest in the empty state and decreased with filling up to 75% of Cmax. From 75% of Cmax to 100% of Cmax, mean Pdet. Increased by 73% (25.2 cmH20 --> 43.5 cmH20), resulting in a 72% increase in mean bladder MCR and a corresponding 36% decrease in mean BBF. Complete bladder drainage led to a drop in mean Pdet. to baseline (0% Cmax) levels while mean MCR remained low, at only 63% of baseline levels with a corresponding mean BBF which was roughly 1.7X baseline, demonstrating a reperfusion phenomenon. Calculated bladder compliance over the entire filling curve correlated directly with BBF (p = .025); i.e. low compliance was associated with low bladder blood flow.

 

Conclusions:

Human bladder blood flow and microcirculatory resistance vary with the degree of bladder filling and the phase of the filling/emptying cycle. In the empty state, despite low intravesical pressure, bladder microcirculatory resistance and blood flow are at their maximum and minimum values respectively. Once filling commences, microcirculatory resistance falls and correspondingly, blood flow increases. When the bladder is filled beyond 75% of its maximum capacity, detrusor pressure rises and microcirculatory resistance is subsequently increased, lowering blood flow. These observations suggest that elevations in bladder wall tension only become significant in reducing BBF when the bladder is near maximal capacity. Acutely after bladder drainage, microcirculatory resistance falls, allowing reperfusion in the collapsed state. Our studies also demonstrated a close correlation between decreased bladder wall compliance and decreased bladder blood flow.