Time-related changes in detrusor overactivity in awake rats with spinal cord injury observed by simultaneous registrations of intravesical and intraabdominal pressures

Abstract

Purpose: To compare the physical characteristics of detrusor overactivity (DO) induced by intravesical infusion of saline in awake, sham rats and rats with chronic spinal cord injury (SCI), by simultaneous registrations of intravesical and intraabdominal pressures.

Methods: Male Sprague-Dawley rats, normal or with a spinal vascular clip at the level of Th9, were investigated cystometrically 1 and 4 weeks after SCI. Intravesical pressure (IVP) and intraabdominal pressure (IAP) were recorded simultaneously to evaluate true DO. During the filling phase, the event of IVP rises, defined as increments that exceeded 2 cmH(2)O from baseline, were determined as DO according to the absence of simultaneous changes in IAP.

Results: All SCI rats exhibited DO during the filling phase, which was not shown in sham rats. The frequency and pressure of DO had a tendency to decrease with time. The DO frequency of SCI rats after 4 weeks (0.9±0.2 min(-1)) was decreased compared with that after 1 week (2.1±0.4 min(-1); P<0.05). The DO pressure of SCI rats after 4 weeks (8.4±1.9 cmH(2)O) was decreased compared with that after 1 week (11.6±2.9 cmH(2)O; P>0.05).

Conclusions: Cystometric studies in awake male SCI rats showed some significant changes in bladder function after SCI. All SCI rats exhibited DO during the filling phase, and showed different physical characteristics of DO over the course of time. The neurological basis of these time-related changes remains poorly understood, but may provide important prognostic information about long-term urological management in SCI patients.

Keywords: Overactive detrusor; Spinal cord injuries; Urodynamics.

Fig. 1

Representative cystometrogram showing detrusor overactivity (DO) with intravesical pressure (IVP), detrusor (DP), and intra-abdominal (IAP) pressures in conscious spinal cord injury (SCI) rats (A), and sham rats (B). The IVP rises during the filling phase were interpreted as DO if occurring without simultaneous similar changes in IAP. DO was shown in SCI rats. Sham rats did not show DO but the abdominal straining.

Fig. 2

The ratio of bladder weight (mg) to body weight (g) (A) and compliance (B) in spinal cord injury (SCI) and Sham rats. The ratio was higher in SCI rats than in sham rats at 4 weeks after the injury. The compliance of SCI rats after 4 weeks decreased significantly compared with that at 1 week. Results are expressed as the mean±standard error of the mean. ^a)P<0.05. ^b)P<0.01 (unpaired Student's t-test).

Fig. 3

The cystometric pressure-related parameters of awake spinal cord injury (SCI) and Sham rats. (A) Basal pressure by detrusor pressure (DP). (B) Threshold pressure by DP. (C) Maximum pressure by DP. Results are expressed as the mean±standard error of the mean. ^a)P<0.05. ^b)P<0.01 (unpaired Student's t-test). NS, no significance.

Fig. 4

The cystometric volume-related parameters of awake spinal cord injury (SCI) and Sham rats. (A) Bladder capacity. (B) Micturition volume. (C) Residual volume. (D) Micturition interval. Results are expressed as the mean±standard error of the mean. ^a)P<0.05 (unpaired Student's t-test).

Fig. 5

Cystometric detrusor overactivity (DO)-related parameters during the filling phase in awake spinal cord injury (SCI) rats at 1 and 4 weeks after the injury. (A) DO frequency. (B) DO pressure. Results are expressed as the mean±standard error of the mean. ^a)P<0.05 (unpaired Student's t-test).