Mean Heart Rate Level Does Not Affect All Heart Rate Variability Indices
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To the Editor:
Monfredi et al1 have put forward an important discussion in Hypertension about an old debate: how basal heart rate (HR) or cardiac interval (CI) levels affect heart rate variability (HRV) indices. The authors elegantly demonstrate, using a biophysical model of sinoatrial node cells, that the higher the HR, the lower the SD of normal to normal beats (SDNN; see Figure 5 of Monfredi et al1). Then, they propose that HRV, represented by SDNN, should be normalized by an exponential decay function, whose parameters were found after fitting the exponential to data from many different studies.
Recently, van Roon et al2 have made a worthwhile comment on Monfredi’s articles, highlighting 2 key points: (1) the ceiling effect of mean HR on HRV is recognized since a long time, as can be seen in a study from Akselrod et al3 and (2) a much simpler normalization procedure is suggested (division of SDNN by the mean CI) which has the same effect as the normalization procedure proposed by Monfredi.
We have no doubt that the mean HR (or CI) level determines the range of variation of the …