Aortic pulsatility and cardio-renal syndrome

Although cardio-renal syndrome has been considered to be a bidirectional pathological link between chronic kidney disease (CKD) and cardiac complications, increased central (aortic) pulsatile haemodynamics may be an additional common underlying pathogenic mechanism, and in the current issue of the Journal, Hashimoto and Ito [1] provide evidence to support this possibility. Central haemodynamics, estimated glomerular filtration rate (eGFR), and standard parameters were measured in a group of patients with hypertension along with B-type natriuretic peptide (BNP) and urinary albumin/creatinine ratio (UACR), biomarkers for cardiac and renal damage, respectively. BNP levels were positively and negatively correlated with UACR and eGFR, respectively, and pulse pressure (PP) showed the strongest correlation with BNP out of the central haemodynamic parameters measured. In the absence of haemodynamic parameters, notably PP and pulse wave velocity (PWV), albuminuria was an independent predictor of a BNP elevation, but not when PP and/or PWV were included in the multivariate logistic analysis model; on the contrary, lower eGFR predicted higher BNP levels in all models. The data are indicative of a shared common mechanism in the context of (micro) albuminuria and raised BNP levels, namely increased aortic PP, whereas the association between reduced eGFR and BNP is mediated by a separate mechanism (possibly volume expansion). The authors’ suggest aortic PP as a possible therapeutic target because it is a common exacerbating factor for both renal and cardiac complications [1]. In this study, positive correlations were observed between plasma BNP and aortic PWV and augmentation index, in addition to aortic PP, and this is in agreement with other studies [2,3]. Although in the discussion, the authors’ relate plasma BNP levels to left-ventricular hypertrophy, the latter seems to be more strongly related to aortic systolic pressure rather than aortic PP [4,5]. Studies using a rat model of CKD, the Fawn Hooded rat, suggest that glomerular hypertension is a major causative factor [6]. A study in normotensive humans demonstrated that wave reflection (including augmentation index) was associated with signs of increased glomerular pressure, namely increased filtration fraction and UACR [7]. In a previous study, Hashimoto and Ito [8] demonstrated that increased aortic PP is closely related to changes in renal haemodymanics, namely the renal resistive index, in patients with hypertension, which the authors considered to be the mechanism responsible for microalbuminuria. However, it is uncertain if and how increased aortic PP increases glomerular pressure or whether glomerular pressure and/or flow pulsatility is a major determinant of UACR. Do increases in aortic pulsatility (aortic banding) cause CKD in animal models? Also, in the context of increased aortic pulsatility, what, if any, is the role of impaired myogenic properties of the afferent arteriole? Impaired myogenic properties of the afferent arteriole are thought to be a key determinant of hypertensive renal injury [9], and impaired myogenic properties of proximal renal arteries have been observed in the Fawn Hooded rat prior to advanced kidney failure [10]. Given the concept of cross-talk between large and small arteries [11], perhaps a shared underlying pathology may also exist. ACKNOWLEDGEMENTS Conflicts of interest There are no conflicts of interest.