ABSENT VASOREACTIVE RESPONSE TO HIGH SODIUM INTAKE COINCIDES WITH SALT SENSITIVITY IN CKD PATIENTS

Abstract

Objective: Chronic kidney disease (CKD) patients are advised to limit salt intake, because of its detrimental effects on blood pressure (BP) and albuminuria. The salt-sensitive BP response in CKD is classically attributed to impaired renal ability to excrete sodium (Na+) resulting in fluid overload. Yet, BP sensitivity to salt is also linked to vasodysfuction, and may even be fluid independent. We aimed to investigate which factor contributes to BP sensitivity to salt in CKD. Design and method: In this randomized crossover study, CKD patients (KDIGO stage G2-3A, proteinuria >0.5 g/d) and healthy controls (HC) followed a 7-day low sodium diet (LSD, <50mmol/d) and high sodium diet (HSD, >200mmol/d), respectively. After each diet, assessment of the hemodynamic profile included daytime BP (Mobil-O-Graph) and cardiac output (CO) measurements (using NexfinTM), by which SVR was calculated accordingly. Extracellular fluid volume (ECV) change was assessed with multi-frequency body impedance spectroscopy (FHCresenius). Results: We included 16 HC (median age 36.0 yrs) and 8 CKD patients (median age 49.5 yrs, and median (IQR) proteinuria 0.6 (0.5-1.1) g/d and plasma creatinine 144 (103 - 167) μmol/l. Dietary salt intervention was successful with median difference in urine Na+ excretion of 242.2 vs 224.6 mmol/day in HC and CKD respectively (p = 0.74). After HSD, the median (IQR) change in systolic BP of patients with CKD was 14 mmHg (4 - 18; p = 0.04), while systolic BP change (4 mmHg (-3 - 8)) in HC was not significant (Fig 1A). After HSD, we observed a significant ECV expansion in both CKD and HC subjects (Fig 1B), but no effect on CO. No associations between HSD-induced BP changes and both ECV and CO were found. Systolic BP increase was correlated with SVR decline in HC, but not in CKD patients (Fig 1C). Conclusions: In contrast to healthy persons, BP salt sensitivity in CKD does not associate with vasodilation. Regarding the absence of differences with ECV and CO between healthy and CKD persons, our data indicate that the incapacity for vasodilation might explain salt sensitivity in CKD.