Intravesical pressure

Habler et al. (1990, 1992) examined the functional properties of unmyelinated and myelinated primary afferent neurons innervating the pelvic viscera in anesthetized cats. The axons were isolated from the intact dorsal root and the intact or chronically de-efferented ventral root of segment S2. The responses of the neurons were studied with natural stimulation of the urinary bladder using innocuous or noxious increases of intravesical pressure. 

The bladder functions as a low-pressure reservoir, filling at the rate of 2 mL/min until approximately 360-400 mL is reached, and the intravesical pressure increases. This pressure activates proprioceptive receptors in the bladder wall to signal the sacral spinal cord, thus triggering detrusor contraction. Sensory stimulation occurs at the micturation center in the brainstem that coordinates urethral sphincter relaxation as the detrusor muscle contracts. Higher controls in the frontal lobe can block this sensory message until conscious direction permits a voluntary void. Medical insults to the spinal column, peripheral sensory nerves, and cerebral cortex will cause malfunction in the voiding pattern (7). 

Steinhardt GF, Goodgold HM, Samuels LD (1988) The effect of intravesical pressure on glomerular filtration rate. JUrol 140 1293-1295... 

The classification of the International Children s Continence Society should be used to eliminate confusion, to facilitate and enable comparative research and metaanalyses. This classification recognizes two main dysfunctions overactive bladder or unstable bladder (urge syndrome) and dysfunctional voiding. The common denominator of lower urinary tract dysfunction is bladder sphincter discoordination leading to chronic high intravesical pressure with resulting negative consequences for the urinary tract. 

By the age of 4-5 years many children have been toilet-trained successfully and have adopted an adult pattern of urinary control. This is also characterized by the absence of involuntary or uninhibited detrusor contractions during bladder fiUing. Even if the bladder is full and there is a strong desire to void, no bladder contractions will occur. With micturition, coordinated relaxation of the external urethral sphincter takes place. Therefore, bladder emptying is under low intravesical pressure in children and adults. 

The child, attempting to maintain continence during such contractions, must voluntarily and tightly constrict the external urethral sphincter to stay dry. This results in simultaneous and unphysi-ological contraction of both the bladder and external urethral sphincter. During this event functional urinary obstruction and high intravesical pressure... 

In vitro experiments demonstrated that menthol (0.1-1.0 mM) inhibited carbachol-induced contraction of the detrusor smooth muscle of rat. Intravesical infusion of menthol (3.0 mM) facilitated the micturition reflex since it caused a reduction in voided volume (by 20%), volume threshold for inducing micturition (19%), and pressure threshold for inducing micturition (31%). This effect on micturition reflex was not modified by pretreatment with capsaicin. This was interpreted to suggest that intravesically infused menthol cannot relax detrusor muscle, and acts on capsaicin-resistant afferents (probably through TRPM8 in urothelium or sensory nerve endings) to facilitate the micturition reflex [15]. 

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