Abstract
A study was carried out to establish a normal range for use in a deep breathing test of cardiac vagal integrity in diabetes mellitus. The change in heart rate resulting from taking a deep breath was recorded in 174 healthy subjects aged 16-89 years. Results were expressed as the ratio of the longest R-R interval during expiration to the shortest R-R interval during inspiration. This ratio declined appreciably with age (p less than 0.001) but was not significantly related to resting heart rate. An age-related normal range was constructed and its diagnostic value investigated in 134 diabetics (aged 15-70 years) with various degrees of neuropathy. The sensitivity for indicating autonomic dysfunction was high: six false-negative and one false-positive result were obtained. Measurement of this age-dependent ratio, which may be made with any electrocardiographic apparatus, provides a simple, accurate diagnostic screen for autonomic neuropathy in the clinic.