Physiology of rectal sensations: a mathematic approach.
OBJECTIVE
The first awareness of balloon inflation (first sensation (FS)), flatus sensation (constant sensation (CS)), urge to defecate (UD), and maximum tolerated threshold (MTT) are the four commonly evaluated rectal sensations. The traditional view that these sensations are attributable to pelvic floor mechanoreceptor stimulation is challenged by current evidence in favor of rectal wall mechanoreceptors. The aim of this study was to determine the physiology of these sensations, using a dynamic mathematic model of the rectum.


METHODS
In a group of 15 healthy adult volunteers (11 female and 4 male; median age, 51.5 (range, 31-74) years), the polynomial behavior of the two smooth muscle components of a dynamic mathematic model of the rectum was analyzed to find strain levels of smooth muscle activity in relation to corresponding strain levels of each of the four "rectal" sensations.


RESULTS
Longitudinal and circular smooth muscle relaxation appeared to be the rate detection and signaling mechanisms, respectively. The latter triggered sensations of CS, UD, and MTT. FS was an anal canal sensation, related temporally with onset of rectoanal inhibitory reflex. In vitro validation of the model suggested MTT to be a physiologic protective mechanism associated probably with tetanic smooth muscle contraction.


CONCLUSIONS
Evaluation of rectal sensations should be confined to CS and UD because MTT is painful and does not contribute any additional information, and FS is not a true rectal phenomenon.
Rao
G N
GN
Academic Surgical Unit, University of Hull, Cottingham, United Kingdom.
Drew
P J
PJ
Monson
J R
JR
Duthie
G S
GS
D000328:Adult; D000368:Aged; D000818:Animals; D003672:Defecation / Q000502:physiology*; D005260:Female; D005414:Flatulence / Q000503:physiopathology; D006801:Humans; D008297:Male; D008465:Mechanoreceptors / Q000502:physiology*; D008875:Middle Aged; D008954:Models, Biological; D009126:Muscle Relaxation / Q000502:physiology; D009130:Muscle, Smooth / Q000502:physiology*; D017773:Pelvic Floor / Q000502:physiology; D011312:Pressure; D051381:Rats; D017207:Rats, Sprague-Dawley; D012007:Rectum / Q000502:physiology*; D012044:Regression Analysis; D015203:Reproducibility of Results; D012677:Sensation / Q000502:physiology*; D012684:Sensory Thresholds