Continuous uroflow cystometry in the urethane-anesthetized mouse

Abstract

Purpose: In vivo animal cystometry represents an accepted methodology for the study of lower urinary tract physiology. A particular advantage of the mouse model is the availability of genetically modified strains, offering the possibility of linking individual genes to relevant physiological events. However, small voided volumes complicate the ability to obtain reliable pressure-flow data by gravimetric methods, due to non-continuous drop formation and release during voiding. We investigated the feasibility of a simple non-gravimetric continuous urine collection system during cystometry under urethane anesthesia, and compared urethane-anesthetized with awake cystometry.

Methods: Cystometry was performed in awake and urethane-anesthetized female mice using a suprapubic tube. A simple, novel non-gravimetric method of urine collection was used in urethane-anesthetized animals to assess voided volume and permit flow rate calculations. Pressure and time-related variables were compared between groups.

Results: Voided urine collection appears to be complete and continuous in this model. Mean voided volume was 0.09 ± 0.020 ml, with an average flow rate of 0.029 ± 0.007 ml/sec. Urethane anesthesia delayed cystometric pressure/volume responses. However, micturition reflexes were intact and otherwise comparable between groups. Female mice void with pulsatile pressurization previously described in rats.

Conclusion: Suprapubic voiding cystometry using a simple and reliable urine collection method under urethane anesthesia is feasible in mice, permitting the integration of voided volumes with pressure and time data. The inclusion of volume and flow data enhances the usefulness of the mouse model for in vivo assessment of detrusor and potentially sphincteric performance.

Fig. 1

Testing of urine collection method. Volume recording at nominal infusion rates of 80, 100, and 120 ml/hr (0.022, 0.028, 0.033 ml/sec). Left graph demonstrates tracing of collection of free falling drops (distance, 2 cm) at 100 ml/hr. Right graph demonstrates tracing of paper-damped collection at 100 ml/hr, as used in urethane cystometry. Error is reported as percentage deviation from nominal infusion rate.

Fig. 2

Examples of voiding tracings in awake (top) and urethane-anesthetized (bottom) animal, acute suprapubic catheterization. Awake tracing is bladder pressure (cm of water) only. Voiding contractions are denoted by arrows in awake tracing (see text). Urethane tracing shows bladder pressure (cm of water, top) and volume voided (ml, bottom). Flow rate is the slope of volume tracing during voiding contraction pressure drop. Each horizontal division = 10 sec.

Fig. 3

Example of time-expanded bladder pressure tracing during voiding. Boxed area illustrates intermittent pulsatile high frequency oscillations (IPHFO) activity during flow. Pressure (cm of water, top tracing) rises per-flow, and flow is accompanied by IPHFO pressure fluctuation. Upon flow termination, pressure rises isometrically prior to dissipation of voiding contraction. Bottom trace is cumulative voided volume (ml). Each horizontal division = 0.5 sec.

Fig. 4

Pressure, time and wall performance data, awake versus urethane murine cystometry. P_max is the maximum voiding bladder pressure (cm of water), P_ctx the voiding contraction pressure threshold (cm of water), P_delta the contraction pressure change (P_max − P_ctx) (cm of water), P_loss the slope of maximal initial voiding pressure decline (cm of water/sec), IPHFO Hz the IPHFO contraction frequency (Hz), P_iphfo the IPHFO contraction pressure rise (cm of water), Interval the start-to-start interval between voiding contractions (minutes), AUC the area under voiding contraction curve (cm of water sec), Compliance the dP/dV (cm of water/ml). Shown are means with 95% CI bars. *P = 0.007, **P = 0.024, ***P = 0.0069.