Can transcutaneous recordings detect gastric electrical abnormalities?

The ability of transcutaneous recordings of gastric electrical activity to detect gastric electrical abnormalities was determined by simultaneous measurements of gastric electrical activity with surgically implanted serosal electrodes and cutaneous electrodes in six patients undergoing abdominal operations. Transient abnormalities in gastric electrical activity were seen in five of the six patients during the postoperative period. Recognition of normal gastric electrical activity by visual analysis was possible 67% of the time and with computer analysis 95% of the time. Ninety four per cent of abnormalities in frequency were detected by visual analysis and 93.7% by computer analysis. Abnormalities involving a loss of coupling, however, were not recognised by transcutaneous recordings. Transcutaneous recordings of gastric electrical activity assessed by computer analysis can usually recognise normal gastric electrical activity and tachygastria. Current techniques, however, are unable to detect abnormalities in electrical coupling.

Colonic and anorectal motility in young women with severe idiopathic constipation.

Forty-four severely constipated women and 16 (8 female, 8 male) asymptomatic volunteers underwent assessment of colon function by (a) clinical examination, (b) rectosigmoid intraluminal pressure recording, (c) colonic transit utilizing radiopaque markers, (d) anorectal manometry, and (e) rectosigmoid electrical activity. Constipated patients were characterized by (a) a greater volume and pressure of rectal distention required for both sensation and sphincter relaxation, (b) diminished basal and postmorphine motility indices only in the distal rectum, (c) delayed transit, and (d) an empty rectum when severely constipated. A neural abnormality affecting afferent nerves may be present in the rectum of female patients with severe idiopathic constipation. Delivery of stool to the rectum is impaired in these patients.

Development of a platinized platinum/iridium electrode for use in vitro.

Silver/silver chloride (Ag/AgCl) electrodes possess excellent electrical properties for measuring the electrical activity of gastrointestinal smooth muscle but exert toxic effects on this tissue in vitro. We thus developed a platinum electrode for use in vitro, the construction of these electrodes relying upon the formation of a glass-platinum/iridium seal. The platinum/iridium (Pt/Ir) electrodes were platinized using a current density of 0.45 mA mm-2. The electrode impedance at 0.01 Hz showed a minimum with platinization current-time products greater than 500 mA s mm-2. However, deposits in excess of 600 mA s mm-2 were readily removed by mechanical abrasion and proved unsatisfactory. Optimal platinization was obtained with a deposit of platinum-black corresponding to a current-time product of 550 mA s mm-2. Optimally-platinized electrodes (geometric surface area 0.11 mm2) had a stable and reproducible potential with a drift of less than 1 microV min-1 and a lower impedance than optimally chlorided silver electrodes (geometric surface area 0.46 mm2) at frequencies higher than 0.25 Hz. The platinized Pt/Ir electrodes were used to record the electrical activity of gastrointestinal smooth muscle in vitro.

Human colonic smooth muscle: spontaneous contractile activity and response to stretch.

The length dependence of the spontaneous contractile activity of human colonic muscle was assessed in vitro. Muscle obtained from the right colon was more distensible than that of the left colon. This was true for all muscle layers. Maximum spontaneous active stress was exerted by both circular and longitudinal muscle layers of the right colon at greater degrees of stretch (p less than 0.001) than those of the left colon. The contractile frequency of longitudinally oriented strips increased with length. The contractile frequency of intertaenial longitudinally oriented strips from the right colon was lower (p less than 0.001) than that of strips from the left colon. The contractile frequency of circularly-oriented strips from the right colon (6.25 +/- 0.38 min) was higher (p less than 0.001) than that of strips from the left colon (3.35 +/- 0.35 min). The human colon appears to consist of two distinct areas based on the mechanical behaviour of the smooth muscle during spontaneous contraction.

Human colonic smooth muscle: electrical and contractile activity in vitro.

Extracellular electrical and contractile activities were recorded in vitro from strips of human colonic smooth muscle obtained at the time of surgery. Serosal electrical activity of longitudinally oriented strips from the taenia and intertaenial region was characterised by continuous oscillation at a frequency of 28 +/- 1/min. Contractions were marked electrically by a series of oscillations upon which spikes were superimposed. The electrical activity recorded from the submucosal surface of circularly oriented strips exhibited oscillations at 24 +/- 4/min, a frequency significantly lower (p less than 0.001) than that recorded from the serosal surface of similar preparations. The contractile force and frequency was dependent upon the part of the colon from which the strip originated; the most powerful contractions were recorded from strips of sigmoid colon. The contractile frequency of circularly oriented strips from the right colon was 6.3 +/- 0.6/min, significantly higher (p less than 0.001) than that of strips from the left colon (3.4 +/- 0.3/min). Stretching these strips caused an increase in contractile frequency to that of the electrical oscillation.

In vitro electrical activity in human colon.

Extracellular electrical activity was measured in vitro in 28 specimens of human colon taken at the time of operation. The mucosa was removed, and the muscle strips were mounted in an organ bath irrigated with oxygenated Krebs. Records were made from 3-7 silver/silver chloride electrodes placed directly on the circular muscle, for periods of 15-30 min. Data were stored on magnetic tape, digitized, analyzed by the fast Fourier transform method and plotted in three-dimensional form (signal power vs. frequency vs. time). Some plots showed a single frequency peak in the range 2-9 cpm, which was present throughout the study. However, multiple peaks were frequently seen and were of two types: (a) peaks of two or three closely related frequencies in the 2-9 cpm range, which divided and fused during the recording time. The power of the fused peak was greater than that of the components. And (b) peaks at frequencies which were integer multiples of the fundamental frequency; we interpret these to be the second and third harmonics of the fundamental frequency. When the fundamental frequency peak developed into several components, similar components also appeared at their individual harmonic frequencies, i.e., the second harmonic components were separated by twice the interval between the fundamental components. We conclude that only one fundamental frequency of electrical activity exists in any one site in human colon. Multiple frequencies are due either to the simultaneous recording from two or more poorly coupled electrical oscillators or to harmonics of the fundamental frequency.