Characteristics and analysis of uterine electromyographic activity in the pregnant sheep.

Myometrial electromyographic activity was recorded with electrodes placed on the uterus in seven pregnant sheep. Electromyographic recordings were made continuously in two groups of animals. One group of four animals was studied for the first 8 days after operation at 60 to 132 days' gestation. The second group of three animals was studied at least 8 days after operation. Myometrial electromyographic activity could be divided into epochs of varying duration. With the use of microprocessor-based data acquisition systems and computerized analysis it was demonstrated that (1) on the basis of an analysis of duration of electromyographic activity there were at least two populations of electromyographic epoch, (2) myometrial electromyographic activity increased in the first 3 to 4 days after operation, and (3) by 6 to 7 days after operation a relatively stable level of activity had been achieved. The separation of electromyographic activity into two populations was most marked in the animals observed in the immediate postsurgical period. In these animals the population of epochs with the longer-lasting activity had a median duration of 5.9 minutes in eight pairs of electromyographic electrodes from four animals. Curve-fitting techniques demonstrated that no more than 14% of uterine electromyographic activity had a duration less than 3 minutes. The longer-lasting group of myometrial electromyographic events corresponds to uterine contractures we have described previously; the other group of epochs of activity was of shorter duration.