The past fifteen years have seen a renewed interest of clinicians and researchers for the evaluation of the sympathetic neural profile characterizing the essential hypertensive state [1]. This was in large part dependent on the discovery of a new therapeutic option represented by the bilateral renal nerves ablation, whose main target is the marked sympathetic overdrive documented in different clinical hypertensive phenotypes, including drug-resistant hypertension [2]. The evidence so far collected in this regard can be summarized as follows. First, by directly quantifying the net release of the adrenergic neurotransmitter norepinephrine from sympathetic nerves in different regional cardiovascular districts, via the norepinephrine isotope dilution method, it has been possible to detect, particularly in resistant hypertension, a marked sympathetic overactivation in the coronary and in the renal circulation [3]. Second, neuroimaging techniques allowing to directly visualize the sympathetic innervation of different organs have also documented an increase in cardiac sympathetic outflow in different hypertensive states [3]. Third, microneurographic recordings of efferent postganglionic muscle sympathetic nerve traffic have provided evidence, confirmed by the results of a recently published meta-analysis, that the neuroadrenergic overdrive is a hallmark of the essential hypertensive state, particularly when a drug resistant hypertensive phenotype is detected [3, 4]. A final methodological approach, which has gained growing popularity during the years as a result of its simple application in a large number of clinical conditions, is represented by the power spectral analysis of the heart rate signal [5]. The approach, however, has been shown to display a number of important limitations in reflecting static as well as dynamic changes in sympathetic cardiovascular drive [3, 6], including those characterizing drug-resistant hypertension.

In the present issue of the Journal of Human Hypertension, De Azevedo et al provide a novel application of the power spectral analysis of the heart rate variability signal, based on an analysis of the low frequency/high frequency components [7]. The analysis has been performed on data collected in four groups of age-matched subjects, classified as healthy normotensives, essential hypertensives with office blood pressure values controlled by a combination drug treatment, resistant and refractory hypertensives, both characterized by uncontrolled office blood pressure values despite the use of more than three antihypertensive drugs and five antihypertensive compounds, respectively [7].