BIOMECHANICAL WALL PROPERTIES OF THE HUMAN RECTUM - A STUDY WITH IMPEDANCE PLANIMETRY

Biomechanical properties of the rectal wall were studied in 17 healthy adult volunteers (nine men and eight women). With impedance planimetr y it is possible to obtain simultaneous measurements of pressure and r ectal cross sectional area (CSA) during balloon inflations. Rectal dis tensions were done with an intraluminal balloon using specified pressu res up to 40 cmH2O above baseline rectal pressure. Balloon inflation e licited a phase of rapid increase in rectal CSA followed by a phase of slow increase until a steady state was reached. Steady state occurred within 67 to 140 seconds with the shortest period at the highest dist ension pressures. Steady state rectal CSA values had a non-linear rela tion to increasing distension pressure. Rectal CSA values in women sho wed a tendency of being slightly higher than male values at all pressu re steps with a significant difference at 3 and 5 cm H2O. Biomechanica l parameters were calculated from rectal CSA pressure relations. Circu mferential wall tension increased in a linear way. Rectal compliance d ecreased in a non-linear way with no further decline between 30 and 40 cmH2O. The pressure elastic modulus increased steeply until a distens ion pressure of 35 cmH2O with no further increase to 40 cmH2O. This su ggests that rectal tone is reduced as the muscle fails to resist furth er distension at 35 cmH2O and higher pressures. Impedance planimetry o ffers new possibilities for investigation of anorectal physiology thro ugh the study of segmental biomechanical wall properties of the human rectum.