Research subjects and methods
Subjects
A total of 132 children, comprising 103 males (78.0%) and 29 females (22.0%) diagnosed with essential hypertension and admitted to the Affiliated Children’s Hospital of Capital Institute of Pediatrics (Beijing, China) from August 2017 to June 2019 were included in this case-control study. The research protocol of this study was approved by the Ethics Committee of the Children's Hospital Affiliated to Capital Institute of Pediatrics. The parents or guardians of the patients received information about the relevant examinations and signed the written informed consent before the study.
Diagnostic criteria and staging of the essential hypertension were in accordance with the Fourth Report on the Diagnosis, Evaluation, and Treatment of High Blood Pressure in Children and Adolescents issued by the National High Blood Pressure Education Program (NHBPEP), 2004 [4]. Stage 1 hypertension is defined as the mean systolic or diastolic blood pressure in the range of 95–99th percentile of children of the same age and gender + 5 mm Hg; stage 2 hypertension is specified as mean systolic or diastolic blood pressure at least 5 mm Hg above the 99th percentile of children of the same age and gender.
Exclusion criteria for this study were patients older than 18 years old; with secondary hypertension caused by kidney disease, vascular disease, endocrine disease, CNS disease, or drugs; or with essential hypertension that had been treated with antihypertensive drugs.
Methods
Determination of blood glucose, blood lipids, electrolytes, and other biochemical indicators
The pediatric patients were fasted for 8 h, followed by the collection of their venous blood in the morning to measure serum sodium and potassium concentrations, plasma cholesterol, triglyceride, uric acid, and other parameters.
Determination of plasma renin activity, angiotensin II level, and aldosterone level
Samples of venous blood were taken from the patients in the morning before eating, and the patients were required to have stayed in bed for more than 4 h. The samples were collected in tubes containing anticoagulants and refrigerated. After centrifugation for 5 min (1000 r/min), the plasma was collected. A Maglumi 2000 Plus automatic chemiluminescence immunology analyzer (Snibe Diagnostic) was used to measure angiotensin II, renin, and aldosterone. Renin activity was assayed using a chemiluminescence immune sandwich method, and the levels of angiotensin II and aldosterone were assessed using chemiluminescence immune competition. The normal reference ranges of angiotensin II, renin, and aldosterone were 25–60 pg/mL, 3.11–41.2 μIU/mL, and 30–160 pg/mL, respectively.
Twenty-four-hour ambulatory blood pressure monitoring
Non-invasive blood pressure monitoring was used, with the daytime measurement taken every 30 min from 09:00 to 21:00 and the nighttime measurement made once every hour from 21:00 to 09:00. The measurements were automatically recorded.
Evaluation of blood pressure variability (BPV)
Dynamic BPV is defined as the 24-h blood pressure fluctuation of the pediatric patients. The indicators used for BPV were the following coefficients of BPV (CV): coefficient of 24-h systolic BPV (24-h SBP (systolic blood pressure)-CV), coefficient of 24-h diastolic BPV (24-h DBP (diastolic blood pressure)-CV), daytime SBP-CV, daytime DBP-CV, nighttime SBP-CV, and nighttime DBP-CV. The calculation of the indicators of evaluation were as follows: CV = standard deviation (SD) of blood pressure/mean blood pressure; 24-h SBP-CV = 24-h SBP SD/24-h mean SBP; 24-h DBP-CV = 24-h DBP SD/24-h mean DBP; daytime SBP-CV = daytime SBP SD/daytime mean SBP; daytime DBP-CV = daytime DBP SD/daytime mean DBP; nighttime SBP-CV = nighttime SBP SD/nighttime mean SBP; nighttime DBP-CV = nighttime DBP SD/nighttime mean DBP.
Indicators for evaluating target organ damage
Heart
The left ventricular mass index (LVMI) and relative wall thickness (RWT) were determined. Cardiac ultrasound was used to measure left ventricular end-diastolic diameter (LVDd), interventricular septum thickness (IVST), and left ventricular posterior wall thickness (LVPWT). According to the Devereux equation, we first calculated the LVM = 1.04 × 0.8 × [(LVDd + IVST + LVPWT)3 − LVDd3] + 0.6, and subsequently calculated the LVMI = LVM/height2.7, as well as the RWT = (IVST+LVPWT)/LVDd. Left ventricular hypertrophy (LVH) was diagnosed if one of the following conditions was fulfilled: a. Male LVMI ≥ 37.08 g/m2.7, female LVMI ≥ 34.02 g/m2.7; b. male and female RWT > 0.36 [5].
Kidneys
Renal damage was diagnosed in the patient if any of the following conditions was fulfilled: Creatinine (Cr) > 0.004 × height × 88.4 μmol/L; Cr clearance rate (Ccr) < 80 mL/min; 24-h urine protein > 150 mg/24 h; urine micro-albumin (MAU) > 19 mg/L; blood beta-2 microglobulin (β2-MG) > 3 mg/L; and urine β2-MG > 0.3 mg/L.
Fundus
Hypertensive retinopathy grade I was contraction and narrowing of the focal arterioles, grade II was retinal arteriosclerosis and presence of arteriovenous cross-signal, grade III was fundus hemorrhage or cotton-wool like exudation, and grade IV was grade III symptoms accompanied by optic disc edema or arteriosclerosis.
Grouping
The patients with essential hypertension were grouped according to their plasma renin activity, or their levels of angiotensin II or aldosterone. Based on the renin activity, patients were classified into a high renin group (> 41.2 μIU/mL, n = 58) and a normal renin group (≤ 41.2 μIU/mL, n = 74). Based on the angiotensin II and aldosterone levels, the patients were classified into a high angiotensin II group (> 60 pg/mL, n = 87) and a normal angiotensin II group (≤ 60 pg/mL, n = 45) as well as a high aldosterone group (> 160 pg/mL, n = 70) and normal aldosterone group (≤ 160 pg/mL, n = 62). Also, the patients were grouped according to the presence or absence of target organ damage. The organ damage-group referred to the patients with damage in one or more target organs, including the heart, kidneys, and fundus. These patients were subdivided into cardiac damage, renal damage, and fundus groups. The differences in plasma renin, angiotensin, and aldosterone levels between groups were analyzed.
Statistical analysis
SPSS 20.0 software (IBM, Armonk, NY) was used for data processing in this study. Normally distributed measurement data are shown as mean ± standard deviation. Independent sample t-test was used to compare the difference between two groups. Analysis of variance (ANOVA) was used to compare the measured differences among multiple groups. Count data are presented as percentages (%), and the chi-square (χ2) test was used to compare the difference between groups. Pearson’s correlation analysis was performed for the variables. P < 0.05 was considered as statistically significant.