T he traditional paradigm of hypertension as a product of increased stroke volume and peripheral resistance 1 has been progressively replaced over the last few decades by a more complex interpretative model, in which the left ventricle and peripheral arteries are functionally coupled with large arteries. The growing scientific interest in the functional properties of the large arteries has been driven primarily by an improved understanding of waveforms and of their modifications in physiological and pathological conditions. 2 Additional factors include the availability of non-invasive devices that are able to accurately estimate large-artery and muscularartery stiffness, 3 and the publication of several clinical studies that have shown the role of arterial stiffness as a predictor of cardiovascular damage and complications. 4,5 Aortic pulse-wave velocity, an index of large-artery stiffness and an independent predictor of cardiovascular complications in different clinical settings, 4,5 has thus been added to the list of factors influencing prognosis in hypertensive subjects, 6 although the need for dedicated equipment and trained personnel has hindered its application in daily clinical practice. A technique to estimate arterial stiffness without the use of special equipment or qualified observers would thus be welcome.By measuring blood pressure (BP) several times in a given individual, possibly under different circumstances, systolic BP (SBP) values can be plotted against diastolic BP (DBP) values. The slope of the relationship between SBP and DBP has been proposed as a theoretically attractive means of investigating large-artery functional properties. 7 In principle, the link between SBP-on-DBP slope and arterial functional properties is rather straightforward. 8 A change in DBP in a given subject is generally accompanied by a change in SBP that goes in the same direction. However, for a given increase in DBP, SBP might be expected to increase more in a stiffer artery than in a more pliable one. Thus, the increase in SBP for a given increase in DBP (SBP-on-DBP slope) could be related to arterial stiffness. The opposite holds for the increase in DBP for a given increase in SBP (DBP-on-SBP slope), which could be considered as a measure of arterial compliance. A slope-derived parameter obtained from 24-h ambulatory BP monitoring, namely the ambulatory arterial stiffness index (AASI), 7 has received great attention from the scientific community, despite the need for caution inherent to the use of a surrogate for more direct measures of arterial rigidity. 9,10 In the present issue of Hypertension Research, Gavish et al. 11 report the findings of a post-hoc analysis of three small studies that examined the effects of season, salt intake and paced breathing on 24-h BP and the related SBP-on-DBP slope. In one study, 13 hypertensive subjects were examined before and after 8 weeks of 15-min daily sessions of slow breathing guided by a device used to lower the high BP. In another study, 17 elderly subjects living in a nur...