Objective: To investigate power spectral analysis (PSA) of heart rate variability (HRV) in children and adolescents with IDDM, its relationship with other measures of HRV and standard cardiovascular responses, and factors associated with reduced HVR.
Research design and methods: A total of 130 subjects with IDDM aged 12.8 +/- 3.2 years and 108 healthy control subjects were studied. Power spectra were analyzed from supine electrocardiograph (ECG) recordings by processing into consecutive R-R intervals and analysis using fast Fourier transformation. Standard cardiovascular responses to deep breathing and standing were performed.
Results: IDDM subjects had a reduction in total power including both low-frequency (0.05-0.14 Hz; P = 0.0001) and high-frequency (0.14-0.40 Hz; P = 0.0002) components. These changes were seen from diagnosis. Other measures of HRV, coefficient of variation (CV) and standard deviation (SD) of mean resting heart rate, were also significantly lower in IDDM. All 20 (15%) of the 130 IDDM subjects with total power less than the 5th percentile in control subjects also had reduced HRV when measured by CV of heart rate. There was an independent relationship between age and the high-frequency component in IDDM subjects and control subjects. Total power correlated with mean heart rate (r = -0.56; P < 0.0001), CV of heart rate (r = 0.90; P < 0.00001), SD of heart rate (r = 0.91; P < 0.00001), heart rate response to deep breathing (r = 0.45; P < 0.0001), and duration in IDDM subjects. There was no correlation with short-term or long-term metabolic control. Retesting of 27 subjects showed a variability in total power and its components comparable to other measures of HRV and standard heart rate responses.
Conclusions: Changes in HRV are a sensitive and reproducible measure of early autonomic dysfunction in childhood. In this age-group, PSA appears no more sensitive a measure of reduced HRV than other closely correlated measures of HRV.