METHODS IN HEART-RATE-VARIABILITY ANALYSIS - WHICH TACHOGRAM SHOULD WE CHOOSE

We investigated the practical impact of the representation of the card iac rhythm - the cardiotachogram - on two elementary spectral indexes in heart rate variability analysis: the low-frequency (0.07-0.14 Hz) a nd high-frequency (0.14-0.40 Hz) powers. Five commonly used tachograms (inter-beat interval function/series, counts, instantaneous heart rat e function/series) were compared. Measurements were done on seven volu nteers in the supine and standing positions. Ratios, and their deviati ons from 100%, of alternative power values were calculated. Mean low-f requency and high-frequency ratio deviations ranged from 0 to 5% and f rom 6 to 37%. The spectrum of counts yielded on average more (15-37%) high-frequency power. Spectra were incomparable without normalization of the tachogram with respect to heart rate. In conclusion, (i) the ch oice of a particular spectrum may lead to differing conclusions on the vagal contribution to heart rate variability and (ii) inconclusive re sults from studies using different tachogram variants can partly be du e to the omission of normalization.