Abstract 4147740: Association of Tissue Sodium with Nocturnal Hypertension and Dipping in Salt Sensitivity of Blood Pressure

Background: Salt sensitivity of blood pressure (SSBP) is an independent risk factor for cardiovascular mortality but the mechanisms are not fully elucidated. Nocturnal dipping of blood pressure, i.e. a decrease in blood pressure during sleep, is considered a sign of a healthy circadian rhythm. The disrupted dipping pattern,known as the non-dipping phenotype, is seen in individuals with SSBP and is associated with nocturnal hypertension and vascular inflammation. Tissue sodium levels are also associated with vascular dysfunction, but their impact on nighttime blood pressure has not been studied. We hypothesized that increased tissue sodium levels are associated with non-dipping pattern in patients with SSBP. Methods: Thirty hypertensive subjects were examined with an inpatient salt loading (SL) and salt depletion (SD) protocol. SL was achieved through saline infusion and a high-salt diet (460mmol/24 hours), while SD was achieved via diuretic administration (furosemide 40mgx3) and a low-salt diet(10mmol/24hours). BP measurements were recorded via ambulatory BP device (Spacelabs 90207). Baseline muscle and skin Na + levels were assessed with the 23 Na MRI technique. Spearman's correlation was used to analyze the associations. Demographic data are presented with mean and standard error of the mean. Results: Participant demographics and clinical data were as follows: age 53 ± 1.34 years,53% female,baseline systolic 140.2 ± 2.62mmHg, diastolic blood pressure 87.30 ± 1.77 mmHg and salt sensitivity index 3.72 ± 1.4 mmHg. While there were no correlations between baseline muscle Na + levels and daytime BP measurements, we found direct correlations with nighttime systolic BP(r=0.56 p=0.0043), mean arterial pressure (r=0.56 p=0.0039) and pulse pressure (r=0.40 p=0.0481) values after SL. Muscle sodium levels inversely correlated with dipping of SBP in SL Day(r=-0.53 p=0.0072). 24-hour total potassium excretion significantly correlated with dipping of SBP on SL day (r=0.65 p=0.0004). We noted an opposite trend in dipping of BP after SD, but this association did not achieve statistical significance (r=0.24 p=0.24). There were no significant correlations between Skin Na + and other measurements. Conclusion: These preliminary findings showed that lower muscle Na + was associated with greater dipping of BP after SL. The trend to reversal of dipping after SD highlights the potential importance of muscle Na + as a dynamic tissue and suggests a relationship with nocturnal BP dynamics.