Evacuation Initiation of defecation is normally under cortical control. As previously discussed, delivery of stool to the rectum stimulates the rectoanal inhibitory reﬂex, permitting sampling followed by accommodation. Further rectal distention results in an urge to defecate. Evacuation occurs with voluntary relaxation of the pelvic ﬂoor muscles (puborectalis muscle and EAS) in conjunction with increased intra-abdominal and intrarectal pressure from Valsalva. This results in widening of the anorectal angle and shortening of the anal canal, which facilitates emptying. Coordinated peristaltic activity of the rectosigmoid assists evacuation. After this process is complete, the closing reﬂex is initiated, resulting in contraction of the pelvic ﬂoor muscles and activation of the continence mechanism.
The epidemiology of anorectal dysfunction has been best defined in terms of the incidence and prevalence of fecal incontinence. Few studies have been done to assess the incidence and prevalence of defecatory dysfunction.
Defecatory Dysfunction The term defecatory dysfunction often is used synonymously with the symptom of constipation. Constipation is an imprecise term used by patients to report a variety of symptoms, including infrequent stools, dyschezia, straining, variation in stool consistency and caliber, incomplete emptying, bloating, and abdominal pain. The most common symptoms associated with constipation are straining and hard stools (2,3). Defecatory dysfunction is defined by many physicians as infrequent stools, typically fewer than three bowel movements per week. This definition is based on stool frequency studies in which 95% of women have more than three bowel movements per week. Using this definition, the prevalence of constipation should be 5% (4). However, the prevalence of constipation has been estimated to range from 2% to 28%, depending on the definition applied (5–7).
There is an increased prevalence of constipation among women and elderly individuals, nonwhite individuals, and those with low income and low education levels (5–7). Based on an estimated 2.5 million visits to US physicians per year for constipation, with an average cost of $2,752 per patient, the annual cost for evaluation of constipation would be approximately $6.9 billion (8,9). An estimated 85% of physician visits results in a prescription; including drug costs would increase this amount substantially (8). More recently, evaluation of 76,854 California Medicaid patients without supplemental insurance found somewhat lower annual total direct costs to care for constipation at almost $19 million ($246 per patient) for this subset of the US population (10). Constipation has a detrimental effect on health-related quality of life (3,10). Constipation contributed to decreased mental and physical scores for quality of life on the SF-36 Health Survey in a Canadian-based population (11).