Participants
All subjects in the present study were participants in an H-type hypertension Registry Study (Registration number: ChiCTR1800017274) conducted in China from March 2018 to August 2018 in Wuyuan, Jiangxi Province, China. The established standards of inclusion or exclusion as well as the data collection approaches related to this study have been described previously [21]. Briefly, this was a real-world observational study of adults over 18 years of age with hypertension as defined by diastolic blood pressure (DBP) ≥ 90 mmHg and/or systolic blood pressure (SBP) ≥ 140 mmHg, or by the use of antihypertensive agents.
Of the eligible patients, 5,233 completed baPWV measurements and were enrolled in the current study. However, 133 patients with ABI < 0.9 were excluded from the study [6],103 individuals with atrial fibrillation [6], 168 patients taking lipid-regulating medications, and 85 individuals with triglyceride levels ≥ 500mg/dl [22]. In total, 4744 individuals were considered eligible for the final assessment (Fig 1). The study got approval from the Ethics Committee of the Institute of Biomedicine, Anhui Medical University, and was also consistent with the Declaration of Helsinki. Patients participating in this study provided their written informed consent.
Clinical data collection
For each patient, demographic characteristics including age, sex, lifestyle (smoking status, drinking status, and labor intensity) medical history (including atrial fibrillation [AF], stroke, diabetes mellitus, and coronary artery disease), and medication usage (including antihypertensive, lipid-lowering, antiplatelet agents, and hypoglycemic). AF was diagnosed based on a medical history and through resting supine standard 12-lead surface electrocardiograms (25 mm/s, 10 mm/mV).
Anthropometric measurements for each participant including weight, waist circumference, SBP, DBP, and heart rate (HR) were obtained by researchers. A validated non-invasive electronic oscillometric device (Omron; Dalian, China) with an appropriate cuff size for the upper arm was used to take four consecutive BP measurements (with a time interval of 1-2 min), with the mean values from the three final recordings being used for analytical purposes to decrease the impact of reactivity on BP. BMI was determined as follows: BMI = weight(kg) /height2 (m2). Diagnosis of incident diabetes was defined as fasting glucose >7.0mmol/l, and/or self-report diabetes during the follow-up period. All research staff involved in this study underwent identical training to ensure consistency.
Laboratory assay
Venous blood specimens were obtained from all patients following a 12 h minimum overnight fasting and were stored at 4℃. Plasma total homocysteine, low-density lipoprotein cholesterol (LDL-c), total triglyceride, fasting blood glucose, high-density lipoprotein cholesterol (HDL-c), total cholesterol, serum uric acid serum creatinine, and blood urea nitrogen levels were quantified with automated clinical analyzers (Beckman Coulter) at the core laboratory of the National Clinical Research Center for Kidney Disease, Guangzhou, China. The entire laboratory’s measurements were obtained in a manner consistent with a standardization and certification program. The estimated glomerular filtration rate (eGFR) was established with the equation of Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI), as in those with higher eGFR levels this equation exhibits superior accuracy as compared to the equation of Modification of Diet in Renal Disease (MDRD) [23]. AIP was calculated as follows: log10 [triglyceride/ HDL-c] with each concentration being presented as mmol/L
Measurement of baPWV
BaPWV and the ankle-brachial index (ABI) were measured on the day of blood sample collection using a BP-203RPEIII networked arteriosclerosis detection instrument (Omron Health Care, Kyoto, Japan). Measurements were conducted in a noiseless room with subjects in the supine position following at least 5 minutes of rest. Participants were not permitted to consume tea, alcohol, coffee, or cigarettes for 30 minutes prior to testing. The measurement approaches of baPWV and ABI related to this study have been described previously [24]. Four cufs were wrapped around ankles and bilateral brachia followed by their connection to an oscillometric pressure sensor and plethysmographic sensor. The ABI was measured by dividing ankle SBP divided with the brachial SBP. Recording the pressure waveforms was carried out with semiconductor pressure sensors for assessing the transmission time between the initial rises in both the tibial and brachial arteries waves. The estimation of the distance between baPWV sampling points was based on height. The formula (La-Lb)/Tba was used for calculating baPWV. Where La represents the distance between the brachium and the heart, and Tba represents the time interval between the ankle and brachial waveforms. An identical approach was used to measure baPWV for all patients, Right and left baPWV values were averaged for analytical purposes.
Statistical Analysis
Continuous data has been presented as means ± standard deviations when normally distributed, or as medians (quartiles) when it is not distributed normally. Categorical variables were given as frequencies or percentages. These three data types were compared using one-way ANOVAs, Kruskal Wallis H tests, or chi-squared tests, respectively. The relationship between AIP and baPWV was assessed using univariate and multivariate linear regression models. Covariates were adjusted for when, if added to the model, they altered the matched odds ratio by at least 10% [25]. To detect non-linear associations, a generalized additive model (GAM) was also applied. When AIP/baPWV ratio was indicated in a smoothed curve, the inflection point was assessed by considering the recursive approach with a maximum likelihood model. Subgroup analyses were conducted with a stratified multivariate regression approach, and interaction analyses were presented in tabulated form. A likelihood-ratio test was used to assess subgroup interactions.
EmpowerStats (http://www.empowerstats.com, X&Y Solutions, Inc, MA.USA) and R (http://www.R-project.org, The R Foundation) were applied for all statistical analyses. A two-sided P < 0.05 was the significance threshold.