Correlation Between Sodium Salt Intake And Heart Rate Variability In Essential Hypertension

Background and objective:Excess dietary sodium salt intake is a major risk factor for salt-sensitive hypertension,and increased sympathetic excitability is an important mechanism of excess dietary sodium salt intake leading to increased blood pressure.However,study shown^[1,2]that dietary salt intake is not only associated with changes in blood pressure,a possible correlation between sodium salt intake and heart rate variability.Heart rate variability（HRV）is one of the foremost noninvasive evaluation of autonomic nervous function.Previous studies on the correlation between dietary salt intake and HRV mostly adopted the dietary method of directly giving altered sodium intake,but the process is tedious,time-consuming and labor-intensive。As the gold standard for the current evaluation of sodium salt intake,24-hour urinary sodium quantification is adapted to be used in the studies for the evaluation of sodium intake^[3].However,there are few studies that use 24-hour urinary sodium quantification to evaluate sodium salt intake and analyze the relationship between sodium salt intake and autonomic nervous function in the early time.Therefore,the purpose of this study is to evaluate the sodium intake in 24 hours urinary sodium quantitatively and to explore the correlation between sodium intake and autonomic nervous function by using HRV as the evaluation method of autonomic nervous function.Material and methods:In this study,we involved 214 patients,including 120 females and 94 males,with essential hypertension in the Department of Hypertension,the first affiliated Hospital of Dalian Medical University from January 2015 to November 2018.Background data including gender,age,height,weight,medication history, previous medical history,smoking history and et al were collected.General diet was given after admission,and fasting venous blood was taken for blood sodium,blood potassium,blood glucose,blood creatinine,blood triglyceride（TG）,total cholesterol（TC）,high density lipoprotein cholesterol（HDL-C）,low density lipoprotein cholesterol（LDL-C）。On the second day after admission,24-hour ambulatory electrocardiogram,24-hour ambulatory blood pressure monitoring and 24-hour urinary sodium were measured.According to the formula,body mass index（BMI）=weight（kg）/height（m）squared,the BMI of all patients was calculated.According to a MDRD formula into the patient’s estimated glomerular filtration rate（eGFR）: eGFR(ml·min^-1·1.73m²)^-1=186 x[serum creatinine（mg/dL）-1.154*age（years old）-0.203*0.742（female）.Automatic calculation of 24-hour ambulatory electrocardiogram HRV index-SDNN,SDANN,rMSSD,PNN50,HF,LF,VLF with Shenzhen bo ying 1.0 Rev 5c.150202 program。According to the quantitative results of 24 hours urinary sodium,the subjects were divided into the low urineary sodium group,the middle urinary sodium group and the high urinary sodium group by using the three-point method.Univariate anova or rank sum test were used to compare the general clinical data and HRV index between the three groups.Spearman simple correlation was used to analyze the correlation between the included indicators such as24 hours urine sodium quantification,gender and age,etc.and HRV.Multivariate linear stepwise regression was used to analyze the relationship between 24 hours urinary sodium and LF,VLF,and P<0.05 was statistically significant.Results:（1）Enrollment status:a total of 214 patients with primary hypertension were included,including 120 females and 94 males,aged 22-79 years,with an average age of 55.8±11.0 years old.The 24 hours urine sodium content was between 32-402mmol/L,and the average 24 hours urinary sodium content was 149.3±76.0mmol/L.The mean systolic blood pressure of the whole day was between 104-166mmHg,with an average of 134.9±12.8 mmHg.The mean diastolic blood pressure of the whole day was 55-116mmhg,with an average of 83.2±9.4mmhg.（2）Clinical background data:According to the 24-hour urinary sodium quantificationvalue,all patients were divided into three groups:（1）Low urinary sodium group:A total of 71 people,including 45 women,26 men;between 25 and 74 years old,average age was 57.2±9.5 years old.The mean systolic blood pressure of the whole day was between 104-153 mmHg,with an average of 130.8±12.1 mmHg.The mean diastolic blood pressure of the whole day was 55-99mmHg,with an average of 79.8±7.4mmHg.（2）Middle urinary sodium group:A total of 73 people,including 42women,31 men;between 22 and 79 years old,average age was 55.8±13.5 years old.The mean systolic blood pressure of the whole day was between 166-112 mmHg,with an average of 135.2±12.5 mmHg.The mean diastolic blood pressure of the whole day was 61-116 mmHg,with an average of 83.2±10.8 mmHg.（3）High urinary sodium group:There were a total of 70 patients,including 33 females and 37 males.The patients were 39-79 years old,with an average of 54.2±9.2 years old.The mean systolic blood pressure of the whole day was between 110-163mmHg,with an average of 138.8±12.7 mmHg.The mean diastolic blood pressure of the whole day was between68-102mmHg,with an average of 86.5±8.5mmHg.There were no statistically significant differences among the three groups in gender,age,proportion of dihydropyridine calcium channel blockers,serum sodium,serum potassium,serum creatinine,eGFR,blood glucose,TC,and LDL-C（P>0.05）.There were statistically significant differences in BMI,TG,HDL-C,mean all-day systolic blood pressure and mean all-day diastolic blood pressure between the three groups（P<0.05）.（3）HRV index:there were no significant differences in all-day average heart rate,SDNN,SDANN,rMSSD,PNN50 and HF between the three groups（P>0.05）.LF and VLF were significantly different among the three groups（P<0.05）.（4）Spearman simple correlation display:There was positive correlation between24-hour urinary sodium quantification and rMSSD（r=0.143,P=0.037）,PNN50（r=0.142,P=0.038）,HF（r=0.142,P=0.038）,LF（r=0.181,P=0.008）,VLF（r=0.200,P=0.003）.The correlation was not significant between 24-hour urinary sodium quantification and all-day average heart rate（r=0.125,P=0.067）,SDNN（r=0.125,P=0.068）,SDANN（r=0.101,P=0.143）.（5）Multiple linear stepwise regression analysis:there was a positive correlation between 24-hour urinary sodium and VLF.Conclusion:In this study,it was found that the HRV index LF,VLF,which reflected sympathetic activity,increased with the quantitative increase of 24-hour urinary sodium,suggesting that sympathetic nerve excitability increased with the increase of sodium salt intake.The HRV index HF,PNN50,rMSSD,which reflects parasympathetic nerve activity,did not change significantly with 24-hour urinary sodium,suggesting that parasympathetic nerve activity did not change significantly with the increase of sodium salt intake.