Original Article

The use of flow equation in functional coloproctology: a new theory in anorectal physiology

  • AHMED FARAG

Pelviperineology 2009;28(1):17-23

The flow equation and hybrid law in coloproctology can be used to understand normal anorectal physiology and accordingly explains the controversies experienced due conflicting research data. It can be used equally for incontinence and constipation. According to the flow equation there are four primary mechanical factors maintaining continence and achieving unobstructed defecation, namely intra-rectal pressure (IRP), dynamic viscosity of the bowel contents, anal canal length and diameter. The last 3 factors are responsible for the anal canal resistance (ACR). All other factors are secondary, and working through one or more of the four primary mechanical factors each can be numerically calculated separately. The sensory and reflex components work through the IRP and ACR respectively, and can also be numerically calculated in each individual. This data can be used to plan treatment and predict outcomes. Calculation of the ACR before and after treatment is helpful when making an objective evaluation of different treatment modalities. If different treatments are given to the same patient, e.g. combining constipating agents with sensory biofeedback for the rectum and anal sphincter repair, each modality may affect a different component in the flow equation, such as the dynamic viscosity, IRP, anal canal length or diameter. Calculation of the ACR also gives new insight into the results of modifying existing treatment modalities or creating new ones. Norm-grams and the automated flow calculator were designed to illustrate and avoid tedious calculations and they suggest a final diagnosis for each patient.

Keywords: Flow equation; Hybrid law; Intra-rectal pressure; Anal canal resistance; Incontinence; Constipation.