The passive and active contractile properties of the neurogenic, underactive bladder

What's known on the subject? and What does the study add? Detrusor underactivity is highly prevalent, particularly in the elderly. It is assumed to result from detrusor failure, although detrusor contractility is often derived from urodynamics studies. Given that detrusor pressure and force are not proportional and urodynamics cannot identify the basis of the pathology, we produced a neurogenic animal model with a highly-compliant bladder and studied detrusor muscle properties, aiming to increase our understanding of the underlying pathology. Highly compliant bladders were characterized by reduced passive wall stiffness and stretched detrusor muscle strips exhibited an enhanced rate of relaxation. These detrusor strips displayed spontaneous contractions that were of greater amplitude (expressed as a ratio of bladder wall stiffness) than those of strips from sham-operated animals; spontaneous contractions increased in amplitude when stimulated by an agonist. These data imply that compliance is not the result of a reduction of detrusor contractility; we hypothesize that altered matrix properties reduce the magnitude with which force can be generated to void the bladder. OBJECTIVE To characterize passive and active changes in detrusor activity in a highly compliant bladder. MATERIALS AND METHODS Bladders from adult female Sprague–Dawley rats were used 5 weeks after lower thoracic (T8) spinal cord transection or a sham-operation. Passive wall properties were assessed by pressure–volume relationships from whole bladders and the tensile response of bladder strips after a rapid (