Population Study On Epidemiology Of Blood Pressure Salt-sensitivity

【Background】Hypertension is one of the cardiovascular diseases,characterized by the raise of arterial,tension originated from hereditary defects and environment risks.The prevalence of the hypertension is increasing worldwide.The prevalence of hypertension in China increased from 5.1%in 1959 to 25%in 2004.It was attributed as the leading potential risk of death cause and 3^rd leading contributor to disease burden.Salt is considered as one important environmental factor that might lead to hypertension.Epidemiology study unveiled a linear relationship between the level of blood pressure and sodium intake.But blood pressure responds to sodium also showed individual variation,which we call it salt sensitivity of blood pressure.Salty sensitivity is now regarded as a mid-phenotype of hypertension heredity.There are many solutions for definition of salt sensitivity,including chronic liquid salt loading, diet salt loading,Sullivan and it's revision.Unified method of salt sensitivity definition is not yet setup..Many factors were involved in salt sensitivity development.Age,body mass index(BMI),baseline blood pressure were found to be related with changes of blood pressure after salt loading.As a mid-phenotype of hypertension heredity,salt sensitivity was previously proved to be sibling cluster. 【Objectives】Main objectives of this study were as below:●Describe the characters of salt sensitivity.●Describe changes of blood pressure across different salt loading peroid.●Sibling aggregation analysis of salt sensitivity.●Analyze the relationship between influence factors of salt sensitivity and changes of blood pressure to salt loading.●Analyze the consistence of sodium and potassium exretion between 24h and 8h urine sample.●Familial aggregation analysis of cold pressor test.●Correlation analysis of salt sensitivity and cold pressor test.●Consistency of salt sensitivity and cold pressor test at follow up test.【Methods】This study is an experiment epidemiological study.173 and their parents from 68 families were recruited through a proband who has an untreated high normal BP or stage-1 hypertension during 2003,siblings took part in baseline,cold pressor test and chronic salt loading,their parents only joined baseline;follow survey,cold pressor test and salt sensitivity test are adopted in 2008.Information was collected on family and personal medical history,lifestyle risk factors,body weight and height,waist and,BP(9 measures from 3 visits),and blood specimens in all participants at the baseline examination;siblings will collect 3 times urine specimens(1 time 24h urine and 2 times 8h urine),and took 1 time cold pressor test.Intervention studies were conducted in the siblings(n=173):1) A low sodium-feeding(3 grams of salt per day) intervention for one week;2) A high sodium-feeding(18 grams of salt per day) intervention for one week;3) An oral potassium supplementation(60 mmol potassium/day) and high sodium-feeding(18 grams of salt per day) intervention for one week.The study intend to describe changes of blood pressure,excretion of sodium and potassium in urine specimens at different study period and compare differences between SS and NSS.To discuss the relationship between salt sensitive associated fators(such as sex, age,BMI and baseline blood pressure) and the extent of blood pressure response to salt loading.To explore the trend of blood pressure changing in different interventions.To perform correlation analysis of sodium and potassium excretion between 8h urine and 24h urine specimens.To determine sibling and familiar aggregation of SS and cold pressor test.To perform correlation analysis between SS and cold pressor test.To determine the forecast action of salt sensitive test and cold pressor test to hypertension.T test and Chi-squre analysis were employed for comparison of continuous and category variables.【Results】1.General information68 families,309 subjects were recruited to baseline survey during 2003-04 with a mean age of 53.20±16.56 and male to female sex ratio of 1.89:1(202/107),173 subjects entered intervention,and 192 subjects joined in cold pressor test.135 subjects reentered the follow-up survey during 2008-2009,with a mean age of 56.74±15.92.Among them,57 and 77 sublings took follow-up feeding intervention and cold pressor test and 77 took cold pressor test specifically.2.Relation of salt-sensitive associated factors with changing of blood pressure response to sodium loading(1) No significant difference had been found on changes of blood pressure between male and female at low and high sodium feeding and potassium supplementation period compared to baseline period.(2) Significant differences had been found on changes of systolic blood pressure between different age groups at low and high sodium feeding periods compared to baseline period,and there had trend of the extent of the diastolic blood pressure and mean arterial blood pressure changing increasing with the age at low and high sodium feeding periods.(3) Significant differences found on changes of blood pressure between different BMI groups at low,high sodium feeding and potassium supplementation periods compared to baseline period,.(4) Significant differences have been found on changes of blood pressure between different baseline BP levels at low sodium feeding and potassium supplementation period compared to baseline period(P＜0.05).But nosignificant difference found between different baseline BP levels at high sodium feeding period compared to baseline period(P＞0.05).3 Characters of sodium sensitivity related factors(1) There is statistical difference between the 24h urinary sodium excretions of SS and NSS,when they suffered high sodium stage(t=-2.22,P=0.028).(2) Both mean arterial blood pressure and 24h urinary sodium excretion were increased after the SS through salt loading(P＜0.05).4 Changes of blood pressure response to potassium supplementationSystolic blood pressure,diastolic blood pressure and mean arterial blood pressure of all subjects and SS were decreasing after potassium supplementation compared to high sodium feeding(P＜0.01);while those of subjects being NSS showed no significant changing.5 Consistence of sodium and potassium secretion between 8h and 24h urinary specimenSodium and potassium secretion showed significant correlation between 8h and 24h urine specimen during different intervention periods(P＜0.05).6 Blood pressure changing during different intervention periodsLow level of blood pressure was presented during low sodium feeding and potassium supplementation period,and the lowest value was seen at 7th day of intervention;while high level of blood pressure was presented during high sodium feeding period,and the highest value was seen at 6th day of intervention. 7 Sibling aggregation of SSDistribution of SS among siblings over 3 members present aggregation status(χ² =19.88,P＜0.01),there were significant correlation between the salt sensitive associated factors(extent of SBP and DBP,sodium secretion of urine) that belong to siblings.8 Familiar aggregation analysis cold pressor test positiveFamiliar distribution of cold pressor positive present aggregation status.Cold pressor related factors were correlated between siblings and parents/children(P＜0.05). But no statistical relevance were found between spouses,even there was a negative relevance.9 Consistence of salt sensitivity and cold pressor testNo correlation was found between salt sensitivity and cold pressor test(χ²= 0.89, P＞0.05),there is a statistical relevance between the recover time of cold pressor test and the 24h urinary sodium excretion of the low sodium stage(r=-0.154,P＜0.05).10 Difference of blood pressure changing by SS and cold pressor test at follow-upChanges of systolic blood pressure,diastolic blood pressure of SS and cold pressor positive are higher than that of NSS and cold pressor negative between baseline and follow-up.Changes of diastolic blood pressure show significant differences(P＜0.01).This indicates that salt sensitive and cold pressor test might predict elevated blood pressure.【Conclusion】Differences of related factors between SS and NSS indicate sodium excretion barrier of kidney and deficiency of pressure natriuresis resconstruction among those being SS.No significant differences of blood pressure changing by gender and BMI;while significant difference was seen between different groups by age and base line blood pressure.Sodium and potassium excretion were found to be consistent between 8h and 24h urine specimen.The minimum blood pressure appearance in 7th day in low sodium and potassium intervention stages,and the maximum value of the salt load stage appearance in the 6th day.Neither the distribution of SS in sibling couples nor the distribution of the positive to cold pressor test in families is consistent with the binomial distribution, there is a aggregation,and the aggregation depend on the common hereditary basis not the influence of similar living environment.There is not uniformity between the results of salt sensitive test and cold pressor test,maybe there is relevance between the factors related with salt sensitive and cold pressor test,the sympathetic nerve activity of SS maybe depend on high sodium.Salt sensitive test and cold pressor test maybe have the function of forecasting the blood pressure increasing.【Suggestions】(1) Family samples need to be extended for better understanding of familiar aggregation analysis of SS and cold pressor test.(2) Strengthen the education of low sodium diet,especially to the SS,control the blood pressure of crowd by decreasing the sodium amount.(3) Because of potassium have the function of decreasing blood pressure,to resist the high blood pressure causing by high sodium;we suggest promoting potassium intervention in the crowd who have high sodium diet.(4) The cycles of the low sodium and potassium intervention stages are all should be 7 days,and the cycle of the salt load stage should be 6 days.(5) To screen the SS and the positive to cold pressor test whose blood pressure easier be higher and adopt earlier intervention to postpone or prevent the hypertension appearance,we should evolve the salt sensitive test and the cold pressor test generally.