The Implications of Spinal Cord Injury on Prostate Compliance

Anthony Y. Yin, AB; M Damaser, PhD; V Wolfe, RN; Inder Perkash, MD; CE Constantinou, PhD

Objectives: Patients with spinal cord injury (SCI) are at increased risk for upper urinary tract infection and renal damage due to compromised innervation of the lower urinary tract. Theoretically, the quantitative diagnosis and treatment of micturition complications can be facilitated by characterization the elastic properties of the prostate, specifically, prostatic compliance. We measured this parameter in order to: (1) examine the effects of compromised neural innervation associated with SCI on prostatic compliance and (2) evaluate the effects of age, diagnosis of benign prostatic hyperplasia (BPH), use of a-blocking medication and surgical history on prostatic compliance specifically within the SCI population.

Methods: Subjects were evaluated during routine diagnostic evaluation at the Urodynamics Outpatient Clinic at the VA Palo Alto Health Care System. A Hitachi linear array system and transrectal probe provided digital ultrasound images used to visualize changes in mid-prostatic urethral displacement during voiding. Bladder pressure and internal sphincter electromyography (EMG) measurements corresponding to these images were also collected to provide functional information. All data were compiled using a Laborie Aquarius urodynamic system. D_detmax, the displacement at maximum bladder pressure (P_detmax), was measured with the aid of computer enhancement of the two-dimensional ultrasound images. Similarly, D_det50, the displacement at half maximum pressure (P_det50) was also measured.

Prostatic compliance, was calculated using the following relationship:

ß^-1=({ln[(P_detmax/P_det50)/(D_detmax- D_det50)/D_detmax]})^-1

Results: For the 17 patients evaluated, overall mean compliance was 0.494± 0.097. The mean compliance for 12 patients with SCI was 0.503±0.097 and for five non-SCI patients 0.471±0.102. In general, SCI did not have a significant effect on prostatic compliance, nor was there a correlation between age and prostatic compliance. However, there was a significant difference in compliance (P=0.02) based on BPH diagnosis (with BPH N=7), regardless of SCI status. Among SCI patients alone, BPH also had a relatively significant effect (P=0.09) on compliance. Among all patients, those with surgical history (N=5) and use of a-blocking medication (N=7) did not have significantly different compliances than other cohorts.

Conclusions: Results suggest SCI has no significant effect on the elastic properties of the prostate during voiding. Likewise, a-adrenergic innervation of the prostatic urethra appears to play a minimal role specifically during micturition. Glandular enlargement associated with BPH (but not age) has the strongest effect on compliance, indicating the relative importance of static/structural factors over dynamic factors on prostatic elastic properties. These findings support the development of pharmacology that focuses on reducing prostate size as a way to alter the viscoelastic properties. Finally, we have established a quantitative assessment tool for characterizing the geomechanical properties of the prostate during voiding that can be useful in directing patient management and urologic care.

Acknowledgment: This study was funded by the VA Rehabilitation Research and Development Merit Review, Grant #B1738-R.