![]() Following the experiment the animal was killed with an intraperitoneal injection of 500 mg of Euthasol. Heart rate and blood oxygenation were monitored with a pulse oximeter on the hindpaw. The animal lay supine on a heated water blanket to maintain body temperature. A catheter (PE50) with a heat-flared tip was inserted into the bladder dome and secured with suture. Female Sprague-Dawley rats (0.267 ± 0.015 kg, mean ± SD, n = 7) were initially anesthetized with 3% isoflurane, followed by two subcutaneous injections of urethane totaling 1.2 g/kg (dissolved as 0.2 mg/ml in 0.9% saline solution). We derive the procedure from a mass balance approach and establish its accuracy by comparing traditional measurements with those obtained using the proposed estimation procedure in both in vivo rat experiments and in computer simulations.Īll animal care and procedures were reviewed and approved by the Institutional Animal Care and Use Committee at Duke University. Moreover, this single measurement is obtained at the end of the experiment, such that it does not interfere with the system during data collection. To address the difficulties in measuring PVR during serial cystometrograms, we propose a procedure that estimates all residual volumes in the series using only a single measurement of PVR. The third is simply to forego any measurement of PVR and all the parameters whose calculation requires PVR. ![]() The second is to neglect the unknown renal contribution to bladder volume, which results in a systematic underestimation of PVR. The first is to remove the PVR after each void to measure it, which is undesirable because removing the PVR does not correspond to the natural physiological conditions the experiment is designed to study. To handle this problem the experimenter is forced to choose among three unsatisfactory options. Therefore, measuring the voided volume alone is insufficient to determine the PVR. During a serial cystometrogram, volume enters the bladder through the catheter, but concurrently volume enters via the ureters at an unknown rate. This approach is useful for quantitative descriptions of bladder function and increasing statistical power, but it is difficult to obtain the PVR of each void in the series. It is common in animal studies to perform a serial cystometrogram by inserting a catheter through the dome of the bladder and continuously infusing fluid to observe lower urinary tract function over repeated voiding events ( 11). Unfortunately, PVR is difficult to measure directly in animal experiments. This is critical information needed to determine the bladder volume as a function of the measured bladder pressure throughout the filling process, which can then be used to estimate bladder tension and compare cystometrograms through time ( 4, 18). Furthermore, PVR allows one to calculate the starting and ending volumes of each voiding event. Therefore, VE is intrinsically normalized to each animal's bladder capacity, which makes it an ideal metric to evaluate bladder function in a heterogeneous population or across differing experimental conditions. VE is the fraction of total bladder volume expelled during the void and is bounded between zero and one. Where V v is the volume voided and V r is the PVR. This, in turn, allows the calculation of other urodynamic parameters that are critical for research studies, including voiding efficiency and bladder capacity. Using the proposed procedure can increase the efficiency and accuracy of determining PVR for a serial cystometrogram and is less disruptive to the system under study. Furthermore, we demonstrate the adverse effects of repeated PVR measurements in a common animal model of cystitis. Using in vivo measurements in urethane anesthetized rats and computer simulations we show that the estimation procedure is at least as accurate in determining PVR as the traditional method of measuring PVR after each void. ![]() We mathematically express PVR for all voids during a serial cystometrogram using a linear recurrence equation and use this equation to build an estimation procedure for PVR. Moreover, this measurement can occur at the end of the experiment such that it does not affect the bladder during data collection. We propose a procedure to estimate PVR during a serial cystometrogram that requires only a single measurement, rather than measuring after each void. Current approaches are to either remove PVR after each void to measure it, which is disruptive to the bladder, or to neglect the unknown contribution to PVR from ureter flow, which results in inaccurate estimates. However, the serial cystometrograms that are typically used to assess bladder function in animal models make measuring PVR very difficult. The postvoid residual volume (PVR) is a common urodynamic parameter used to quantify the severity of lower urinary tract dysfunction. ![]()
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