COMPARISON OF DIFFERENT METHODOLOGIES OF HEART-RATE-VARIABILITY ANALYSIS

Two methodological aspects of heart rate variability (HRV) are tested. Heart rate variability and RR interval variability (RRV) are compared in 109 healthy subjects using 24-h Holter recordings. Autoregressive power spectrum analysis was performed, and the power in three frequenc y bands was evaluated by two different methods: the peak power and the mean power within the band. The power in the low frequency (LF) and h igh frequency (HF) ranges showed greater changes between day and night values when RRV was analysed compared with HRV. The mid frequency (MF ) range power showed no significant change at night with RRV analysis compared with a significant decrease with HRV analysis. The different pattern of changes between day and night values when using RRV or HRV analysis is explained by the non-linear nature of the relationship bet ween RR interval and heart rate and the lower heart rate at night. The refore, depending on the heart rate, there may be amplification or att enuation of fluctuations when transforming from one heart rate variabi lity method to another. When comparing peak power and mean power measu rements within the frequency bands, the changes in LF and MF powers we re similar. However, HF mean power with RRV analysis showed less chang e at night than the peak power and no change with HRV analysis. The ex planation lies in the fact that respiratory fluctuations at night are much more regular, resulting in a sharp high peak in the power spectru m. The peak power is therefore higher alt night, whereas the total pow er changes much less or remains unchanged. The results of the present study may help resolve conflicting results when different methodologie s are used.