314
CHAPTER 26
tion before the bladder is sufficiently distended to act reflexly. Conversely, these influences
may inhibit vesical emptying in spite of desire or stop the flow of urine abruptly once it
has started. Prostatectomy may not necessarily prevent the ability to stop the urine flow
at will. The effect of stressful psychiatric interview on raising intravesical pressure has
been demonstrated by Straub
el al.
(1950). The emotional incontinence in subjects with
cerebral atherosclerosis or brain tumours is well known. On the other hand, normal
subjects may, through embarrassment, have difficulty in overcoming their inhibition
to micturate at will or on desire in the presence of a doctor or nurse. In others the visual
or auditory stimulus of running water may be necessary to facilitate volitional voiding.
This practice is sometimes adopted in training children.
Posture also has an influence on the ability to micturate, and certain normal subjects
are unable to pass urine in supine position even by using strong abdominal pressure.
Others are able to pass only small quantities of urine in that position and moreover, the
rate of urine flow is diminished, and greater or lesser quantities of residual urine result.
While the active contraction of the abdominal muscles during the act of defaecation
is essential, their degree of action in the act of micturition varies considerably from
individual to individual of both sexes according to circumstances. Certain individuals
use abdominal pressure only at the end ofmicturition. Denny-Brown & Robertson (1933)
found that abdominal wall contractions were not necessary to initiate and sustain micturi
tion. They also observed 'after contractions' at the end of voiding which were associated
with an increase in intrarectal pressure and contraction of the abdominal muscles. These
after contractions which were particularly pronounced when the urine volume was small,
were not considered to be the result of rise in abdominal pressure. Electro-myographic
studies have confirmed the variability of muscular activity of the abdominals in micturi
tion on desire or volition (Bors, 1963). However, the flow rate of urine depends, apart
from the volume, on the action of the abdominals and diaphragm in raising intra-
abdominal pressure.
Wilful suppression of desire to micturate leads to temporary inhibition and relaxation
of the detrusor muscle, in the same way as volitional suppression influences the function
of colon and rectum, which clearly indicates control of central stations of the nervous
system on the function of smooth muscles. Protracted suppression of releasing the
distended bladder normally sets up a feeling of considerable discomfort leading eventu
ally to irresistible urge to micturate accompanied by more or less pronounced cardio
vascular and other responses of autonomic mechanisms such as shivering, piloerection
and sweating. Habitual restraining of micturition in spite of large fluid intake, as is the
case in excessive beer or tea drinkers, results in increasing bladder capacity and may lead
eventually to chronic over-stretching of the detrusor muscle and reduction of its expul
sive power. These pre-paraplegic, individually varying habits of micturition, should
always be taken into consideration when dealing with patients suffering from bladder
dysfunction due to affliction of the nervous system, in particular in spinal paraplegics
and tetraplegics.
The question of sequence and latency in the reciprocal action between the detrusor
muscle and the internal and external sphincter complex and muscles of the pelvic
floor is still a matter of controversy (Denny-Brown & Robertson, 1933; Hinman
et al.,
