Time-frequency analysis of heart rate variability

The heart rate variability (HRV) is effected by the presence of diabetes mellitus (DM). Specifically, the power spectral density (PSD) of the HRV is perturbed in specific frequency ranges. This study presents the algorithm employed to extract changes in the PSD due to the onset of DM. In particular, streptozotocin (STZ) is administered to test animals in order to impair the insulin producing, pancreatic b-cells and thus model the onset of DM. The treated animals display symptoms of Type 1 DM including hypoinsulinaemia and hyperglycemia. In order to index the progressive effect of DM on the HRV PSD, five minutes of rat (n=12) electrocardiogram (ECG) were acquired hourly for 30 days. At day 10, half the animals were treated with STZ. The HRV signal was extracted from ECG and the short-term frequency transform (STFT) was used to estimate the 24 hr PSD. At 3 days after STZ-treatment, the animals were shown to be diabetic and at 5 days, the HRV PSD displayed a significant depression in the higher frequencies with a 3.3 Hz centered trough.