Stability of myoelectric slow waves and contractions recorded from the distal colon

The stability of physiological activity in the distal colon was investigated by recording 5-6 hours in each of 6 healthy adults. Contractions and myoelectric slow waves were recorded from the sigmoid colon (25-30 cm from the skin surface) and rectum (10-15 cm), and pressure waves were recorded from the proximal small intestine. The activity index (sum of areas of all waves divided by recording time) varied by 200% to 800% across 4-min samples for all motility and myoelectric slow wave recordings. Spectral analysis indicated that contractile activity waxed and waned in a cycle with a period of 40-55 min in the colon and 64-80 min in the small intestine. Myoelectric slow wave activity in the colon cycled with a period of 30-40 min. Contractile activity in the sigmoid colon was correlated with similar activity in the rectum, but myoelectric slow wave activity in the colon was not correlated with myoelectric slow waves in the rectum. The frequency composition of contractions and slow waves was unstable over time.