1986 Volume 19 Issue 19 Pages 91-96
The existence of a circadian rhythm on the electrocardiogram was studied in 20 dogs. Statistically, it was confirmed in 7 measuring items: heart rate, P-R interval, Q-T interval, P wave amplitude, P wave duration, R wave duration, and S wave duration.
From 8: 00 a.m. to noon, P, R, and S waves showed tendencies to increase in interval and to decrease in voltage. From 8: 00 p.m. to midnight, however, they tended to be short in duration and to increas in voltage.
The average of circadian rhythm in the 20 dogs moved to a normal value. In individual dogs however, it was not a little lear that each measuring item moved both internally and externally from a normal range.
