Circadian disruption and surgical recovery

Circadian rhythms were investigated in rats following surgery, as measured by body temperature and locomotor activity, and postoperative recovery was measured by activity level. Eight randomly selected Sprague-Dawley rats were implanted with radio temperature-transmitters under general anesthesia. Timer-controlled cassette recorders recorded body temperature at predetermined intervals. To monitor activity, the rats were placed in individual metabolic cages equipped with infrared-sensitive locomotor activity monitors. Temperature was sampled hourly. Activity was measured continuously and summed every 15 minutes for sampling. Measurement was begun before surgery and continued from 12 to 20 days following surgery, depending on when the animals regained their typical rhythmic patterns. Temperature and activity rhythms were altered and uncoupled from external cues in a manner similar to that previously found in humans. The animals demonstrated individual variation in their return to presurgical activity levels. Six days after surgery, the rats experienced a second period of disrhythmic and decreased activity. Rats with the greatest activity phase-shifts took longest to return to presurgical activity levels. This suggests that the degree of circadian alteration following surgery is positively related to the time required for recovery and reentrainment of rhythmicity.