Heart rate changes in diabetes mellitus.

Resting heart rates were measured lying, sitting, and standing in 61 diabetics with varying degrees of cardiovascular reflex abnormalities. Those with parasympathetic abnormalities alone had the highest heart rates, while those with both parasympathetic and sympathetic involvement had slightly less rapid heart rates, which were still faster than those in diabetics with normal cardiovascular reflexes. 38 other diabetics in whom autonomic function tests had been done at least three times had a similar pattern of resting heart rate. 25 had unchanged tests: those with parasympathetic involvement alone had the highest heart rates. The other 13 subjects whose autonomic function changed from normal to abnormal showed a sequential increase in heart rate as cardiac parasympathetic damage developed, followed by a fall in heart rate, but not back to normal, as sympathetic damage developed as well. The increased resting heart rates in diabetics may be due in some patients to cardiac parasympathetic damage alone and in others to combined parasympathetic and cardiac sympathetic damage. The sequential heart rate changes support the view that the vagus nerve is affected before the cardiac sympathetic nerves.