Prediction and consistency of blood pressure salt-sensitivity as assessed by a rapid volume expansion and contraction protocol

Background: This multicenter trial in essential hypertensive patients (n=94) is aimed i) to evaluate the distribution of blood pressure salt-sensitivity by a rapid volume expansion/contraction protocol over three days; ii) to investigate the within-patient reproducibility and to identify predictors of the response to the test; iii) to compare this response with the response to dietary NaCl restriction. Methods: The study design included: 1) screening for salt-sensitivity by the rapid test; 2) a controlled trial of dietary salt restriction; 3) repetition of the rapid test in a subgroup of patients. Results: The mean BP response to the rapid test fitted a Gaussian curve. In multivariate regression analysis, controlling for the effect of potential confounders, the blood pressure increment during the intravenous saline infusion was the best independent predictor of the response to the test (r=0.713) with minor contributions by the 24-h urinary sodium excretion before the test and by baseline fasting serum insulin. These three variables together explained 61% of the overall variability of the response. The Spearman rank correlation coefficient between the BP response to the rapid test and the response to the dietary protocol was 0.21, p=0 05. Upon repetition of the rapid test, the correlation coefficient between the responses observed on the two occasions was 0.60 (n=19, p<0.01); there were no patients misclassified across the extreme tertiles of the distribution of salt-sensitivity. Conclusion: We conclude that the rapid test reproducibly identified patients in the upper and lower parts of the distribution of salt sensitivity. The analysis of possible predictors of the response to the test suggested that the evaluation of the blood pressure response to saline infusion, upon careful standardization of dietary NaCl intake, may represent an alternative to the completion of the whole test for the screening of the salt-sensitivity.