Cardiac Beat to Beat Variation: Age Related Changes in the Normal Population and Abnormalities in Diabetics*

Determination of heart rate variation (RR interval variation) is a non‐invasive technique which may be used for assessment of diabetic autonomic dysfunction. Interpretation has been complicated by age changes in the normal population and by uncertainty as to the optimum conditions for the performance of the test. This study was designed to establish a normal age‐related range for RR interval variation performed under the simplest conditions (resting, seated) applicable to an outpatient diabetic clinic and to compare these measurements with augmented RR variation due to deep breathing (ARRIV) and with the Valsalva ratio (VR ). Using an ECG recorder and a computer analysis program, resting RR interval variation (RRIV) was assessed in 100 non‐diabetics (N) aged 12–80 years and 60 randomly selected diabetics (D) aged 14–74 years. RRIV, the standard deviation of RR intervals, declined progressively after age 40 in normal subjects. The diabetics had significantly (p < 0.001) reduced RRlV compared with normals; 65% having RRIV values more than 1 SD and 25% more than 2 SD below the age related mean for normals. RRlV was compared with ARRIV in 54 subjects (N40, 014) and with VR in 84 subjects (N54, D27). There was a significant correlation of RRlV with both indices but RRlV resulted in greater discrimination between N and D than ARRIV or VR. There was no significant correlation between RRlV and duration of diabetes but mean RRlV was significantly reduced in diabetics with peripheral neuropathy compared to those without. In seven diabetics studied both before and after substantial improvement in metabolic control RRlV improved by a mean of 51% (p < 0.005). Measurement of RRlV is a simple non‐invasive technique for assessment of diabetic autonomic dysfunction. Interpretation, however, depends on knowledge of an age‐related reference range.