The “simultaneous contractions” of the human colon are a fast propagating rhythmic neurogenic motor pattern associated internal anal sphincter relaxation and gas expulsion, not an artifact of abdominal pressure changes

So called “simultaneous contractions” are the most abundant motor pattern of the human colon in 24 hr manometry recordings (1), yet we know little about their origin or function, in part because many suspect them to be artifacts of abdominal pressure changes. This motor pattern was assessed by High Resolution Manometry (36 sensors, 1 cm apart) in 30 patients with idiopathic constipation or IBS and volunteers to evaluate their use in assessing neurogenic pathology. “Simultaneous contractions” had a propagation velocity > 7 cm/s, an amplitude between 5 and 60 mm Hg. They held the colon in a tonic contraction for 10–20 s over the measured 36 cm, often highly rhythmic at 1.5 – 2 cpm. They were by far the most significant motor pattern causing bowel sounds and/or gas expulsion. A typical “simultaneous contraction” was associated with many haustral boundary contractions. When the internal anal sphincter pressure was recorded at the same time, relaxation was observed in synchrony with the “simultaneous contractions”, even if they were of very low amplitude (<5 mm Hg) indicating that it was not rectal contraction or distention but a neural program that induced IAS relaxation. We believe the simultaneous contractions to be the motor equivalent of electrical activity termed “rushes” with a velocity of 10.5 ± 2.6 cm/s (2). Hence “simultaneous contractions” are fast propagating contractions orchestrated by a neural program that includes anal sphincter relaxation. Its rhythm may be linked to neurally induced pacemaker activity of the intramuscular interstitial cells of Cajal. Supported by grants from the National Natural Science Foundation of China and the Canadian Institutes of Health Research.