Cardiac beat-to-beat variation as an indicator of neuropathy and the frequency of its abnormality in diabetes mellitus.

The cardiac beat-to-beat variation and the maximum constriction velocity and acceleration of the pupillary light reflex have been considered indices of parasympathetic neuropathy. The abnormality of these indices was evaluated in 191 non-diabetics and 151 diabetics. The cardiac beat-to-beat variation decreased gradually with age in non-diabetics as well as diabetics. It was small in diabetics compared to non-diabetics in corresponding age group between 10 and 59 years. In diabetics it was still smaller in the presence of peripheral neuropathy than in its absence. The overall prevalence of this abnormality was 30.1% in diabetics but only 3.0% in non-diabetics. In diabetics it rose to 40.0, 42.6 and 52.2% in the presence of motor, sensory and motor plus sensory nerve neuropathy, respectively. In 63 diabetics examined for both cardiac beat-to-beat variation and pupillary light reflex, no statistical difference was observed between the frequency of these abnormalities. These observations indicate an extremely high prevalence of abnormality in autonomic nerve function in diabetics especially in the presence of abnormality in autonomic nerve function in diabetics especially in the presence of other types of neuropathy, so that diabetics with peripheral neuropathy should be carefully examined for autonomic neuropathy and vice versa. Besides, the measurement of the cardiac beat-to-beat variation is similar in sensitivity in the detection of neuropathy to the measurement of pupillary light reflex.