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Heart rate variability: how to assess effects of mild therapies on autonomic control in small groups of mild and borderline hypertensives?

To the Editor: 

In their recent retrospective study, Singh et al1 could demonstrate on the basis of the impressively huge data set of the Framingham Heart Study that, first, short-term heart rate variability (HRV) is reduced in men and women with systemic hypertension and, second, among normotensive men, lower HRV was associated with a greater risk for developing hypertension. The authors concluded that autonomic dysregulation is present in the early stage of hypertension. Their findings are important but were not very surprising because the reported HRV reduction was generally in accordance with findings of earlier studies.2 However, what they inevitably left out of consideration was the analysis of the diurnal variation of blood pressure, heart rate, and their respective variabilities. Particularly, the asleep/awake ratios of blood pressure are probably more specific and sensitive than temporary daytime parameters.3 From the methodical point of view, the study was characterized by the strong and uncompromising use of statistics, but unfortunately without showing any raw data, eg, by using scatter or box plots of the blood pressure and HRV data. Moreover, one important question remained unanswered: How did the HRV parameters and the covariates change during 4 years of follow-up?

Independently and without knowledge of the results from the above study, we also studied the differences of linear and nonlinear HRV parameters in (only) 25 essential nontreated hypertensive subjects with respect to their status of hypertension. The study was carried out from Spring …