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.
All blood pressure measurements were performed using the auscultation method as recommended by the Fourth Report on the Diagnosis, Evaluation, and Treatment of High Blood Pressure in Children and Adolescents, and the results were used for hypertension diagnosis and stage classification [10]. Hypertension was diagnosed when the average systolic and/or diastolic BP was ≥95th percentile from the auscultation measurement on at least 3 separate occasions adjusted for gender, age, and height. Stage 1 hypertension was diagnosed if a child’s BP was greater than the 95th percentile but less than or equal to the 99th percentile plus 5 mmHg; and stage 2 hypertension was diagnosed if a child’s BP was greater than the 99th percentile plus 5 mmHg.
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.
Laboratory examinations
Blood lipids, electrolytes, and other biochemical indicator measurements
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.
Plasma renin activity, angiotensin II level, and aldosterone level measurements
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, 0.15–2.33 ng/mL/hr, and 30–160 pg/mL, respectively.
Ambulatory blood pressure measurement
All patients underwent 24 h ambulatory blood pressure monitoring using a DMS-ABP device (DM Software Inc, Beijing). Information on the procedure and the device was provided to the patients. In order for the device to function properly, patients were told to perform their daily activities normally, but to remain immobile during measurements. BP recordings were programmed to occur every 30 min during the day and every 60 min while sleeping.
Sleep and wake times were recorded and adjusted for each patient to define the nighttime period. On the basis of these measurements, 24-h systolic blood pressure (24-h SBP), 24-h diastolic blood pressure (24-h DBP), daytime SBP, daytime DBP, nighttime SBP and nighttime DBP were determined. The method was considered reliable if >75% of the measurements were valid.
Blood pressure variability was calculated using the average real variability (ARV) index;
ARV was calculated mathematically using the numerical variation between two successive measurements, as shown in the formula below: (see Equation 1 in the Supplementary Files)
where N is the number of valid blood pressure measurements, and BPk+1 and BPk represent two successive blood pressure measurements. The rationale for selecting the ARV index for blood pressure variability calculation was based on earlier reports stating that the ARV index was a more reliable index for establishing the prognostic significance of blood pressure variability [11].
Indicators for evaluating target organ damage
Heart
LVH was assessed using echocardiography. Left ventricular internal dimension (LVIDd), interventricular septal thickness (IVST), and left ventricular posterior wall thickness (LVPWT) at the end diastole were measured using the Philips iE33 Ultrasound System. Left ventricular mass (LVM) was calculated as LVM=1.04 × 0.8 × ((LVIDd+IVST+LVPWT)3–LVIDd3 )+0.6 [12]; and LVM index (LVMI) was calculated as LVMI=LVM/height2.16; and relative left ventricular wall thickness (RWT) was calculated as RWT=(IVST+LVPWT)/LVIDd; For the diagnosis of LVH, LVMI ≥ 45 g/m2.16 or RWT> 0.41 was considered abnormal[13,14].
Kidneys
Renal damage was diagnosed in the patient if any of the following conditions was fulfilled: albuminuria (urinary albumin/creatinine quotient) >3 mg/mmol creatinine; 24-h urine protein excretion > 200 mg/m2/day [15, 16].
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 (> 2.33 ng/mL/hr, n = 58) and a normal renin group (≤ 2.33 ng/mL/hr, 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 patients in the organ damage-group were subdivided into cardiac-damage and renal-damage 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. Univariate associations between the indices of RAAS levels, LVMI, and other variables of TOD were assessed through simple linear regression analyses and Pearson correlation coefficients. P < 0.05 was considered statistically significant.