Urinary flow rate in benign prostatic hypertrophy in relation to the degree of obstruction of the vesical outlet.

Forty men with bladder outflow obstruction from benign prostatic hypertrophy were investigated urodynamically by medium-fill water cystometry and pressure flow study. The most obstructed patients proved to be unstable. A positive link was found between the degree of obstruction, as assessed by the opening pressure (i.e. the detrusor pressure needed to start micturition), and the maximum mechanical power generated by the contracting bladder during voiding. What seems most striking, is that neither detrusor contraction velocity nor the urine flow rate fully mirrored the degree of obstruction--i.e. the opening pressure and the maximum contraction speed did not show a negative correlation, but rather a weak (though insignificant) positive link, and the flow rate decreased only slightly (not significantly) when obstruction increased. Such a surprising observation could be explained by the fact that prostatic obstruction produces both collagen infiltration into the bladder muscle (this affecting the spread of the depolarisation wave) and, at the same time, denervation supersensitivity. The latter actually yields a decrease in electrical resistance between the detrusor smooth muscle cells (and thereby an enhanced synchronisation of the detrusor contraction), which might be only partly cancelled by the effects of collagenosis.