#4777 BLOOD PRESSURE RESPONSE TO A LOW SODIUM DIET IN NORMOTENSIVE SUBJECTS

Abstract

Abstract Background and Aims The term salt sensitivity (SS) has been used to show an increase in BP in response to saline overload in both normotensive and hypertensive patients. Age, sex, and obesity have been proposed as predisposing factors. The objective of our work was to evaluate the response of office BP (OBP) and ambulatory BP (ABP) to changes in salt intake in healthy normotensive subjects. Method We analyzed 193 subjects who participated in the evaluation as potential kidney donors; none had a history of hypertension, diabetes, renal or cardiovascular disease. They received two consecutive standardized diets, one with 300 mEq and the other with 30 mEq of Na+/day. On the last day of each diet, a 24-h urine collection was obtained and an ambulatory BP monitor was placed for 24 h in the non-dominant arm, following recording of OBP. Data were expressed as mean and standard deviation (SD). Student's test and one-way ANOVA were used to compare means, values of p<0.05 were considered statistically significant differences. Results In the study group there were 120 females (62%) and 71 were salt sensitive (SS) (37%). The mean age was 46.9 ± 10 years (20 – 72) without significant gender differences (F = 46.7 ± 10 vs M = 47.3 ± 9 p = 0.704). The age of the salt sensitive (Ss) group was significantly higher than the salt resistant (Sr) (49.8 ± 9 vs 45.3 ± 10 p = 0.002). BMI was found to be increased (27.7 ± 4) without significant gender or incidence of SS differences. We found no association between gender and SS (p = 0.509). After the high sodium and before low sodium diets, the mean difference in urinary Na+ excretion was 165.2 ± 83 mEq/24h, significantly higher among men than women (201.6 ± 84 vs 142.3 ± 75 p = 0.0001). There were no differences based on SS. We did not find significant gender differences in the variation of OBP or ABP, with the changes in the diet. The mean reduction of systolic pressure OBP for the group was 6.13 ± 10 and of diastolic pressure OBP 0.35 ± 5 mmHg. In separate analysis, systolic and diastolic OBP drops were significantly higher in the Ss than in the Sr (9.69 ± 12 vs 2.57 ± 8 and 2.24 ± 7 vs – 0.95 ± 5 mmHg respectively, p = 0.001). The average reduction in systolic ABP was 7.13 ± 8 and in diastolic ABP 3.33 ± 5 mmHg. In separate group analysis we also observed a significantly greater reduction in Ss than in Sr (12.83 ± 7 vs 1.8 ± 5 and 6.56 ± 5 vs. 0.12 ± 3 mmHg respectively, p = 0.001). Conclusion In our study group, the reduction of both OBP and ABP following a low sodium diet in normotensive subjects depends on salt sensitivity and is independent of gender and body weight.