2.1 Study design and participants
In this cross-sectional study, we reviewed the medical records of the Zhejiang Provincial People’s Hospital in Zhejiang, China and identified 586 adults (>18 years old) with a diagnosis of CKD who had underwent CABP measurements between January 2017 and May 2019. CKD is defined as abnormalities of kidney structure or function, present for > 3 months, with implications for health. Patients with a history of general or local vasospasm (such as that following hypothermia in cardiopulmonary bypass surgery, or of Raynaud’s phenomenon), aortic stenosis (gradient > 60 mmHg), or a SphygmoCor system operation index ≤ 80 were excluded from the study. Finally, 289 patients were eligible for analysis.
This study was approved by the Medical Ethics Committee of Zhejiang Provincial People’s Hospital, and was conducted in accordance with the Declaration of Helsinki (as revised in Brazil 2013). Written informed consent was obtained from each participant prior to inclusion.
2.2 Data collection
Demographic data such as age, gender, weight, height, history of smoking and drinking, duration of diabetes and hypertension, previous medical history, and current antihypertensive medication usage were collected. Whole blood samples (5–10 mL) were collected from each participant after 12–14 h of fasting to perform comprehensive blood analyses including albumin, glucose, blood urea nitrogen, creatinine, estimated glomerular filtration rate (eGFR), uric acid, potassium, sodium, calcium, magnesium, phosphate, total cholesterol, triglyceride, low-density lipoprotein cholesterol, haemoglobin, and platelet count. Regarding physical examination, the heart rate, BABP, height, and weight were measured by two clinicians in a quiet environment.
The eGFR was estimated according to the modified Modification of Diet in Renal Disease (MDRD) formula:
eGFR (mL/min/1.73m2) = 175×Scr-1.234×Age-0.179 (×0.79, if female)
in which Scr is the serum creatinine.[12] The body mass index (BMI) was calculated by dividing the body weight (in kilograms) by the square of the height (in meters).
2.3 Echocardiography
All echocardiographic examinations were performed by trained ultrasound physicians, in accordance with the American Society of Echocardiography guidelines.[13] The left ventricular mass (LVM) was calculated using the formula:
2.4 Blood pressure measurement
2.4.1 CABP measurement
CABP measurements were obtained in the supine position after 10 minutes of rest, using the SphygmoCor® CvMS (AtCor, Australia, 2013) device and software. The Sphygmocor® operates through a tonometer placed on the right radial artery and is calibrated by standard cuff blood pressure. The Sphygmocor® CvMS CABP analysis option provides a derived ascending aorta waveform and a series of central artery indexes. The generalized transfer function of the SphygmoCor® software was used to estimate the CABP profile. Central systolic blood pressure (CSBP), central diastolic blood pressure (CDBP), central pulse pressure (CPP), augmentation pressure (AP), pulse wave velocity (PWV), augmentation index (AIx) and augmentation index adjusted for 75 beats per minute of heart rate (AIx@75) were registered for analysis. To ensure consistency between measurements, recordings were discarded if the operator index was < 80%.
2.4.2 BABP measurements
BABP, including brachial systolic and diastolic blood pressure (BSBP and BDBP, respectively) was measured using the standardized American Heart Association protocol. Trained staff obtained three manual readings in the seated position after at least 10 minutes of rest.
2.5 Statistical analysis
We categorized patients into two groups according to the presence or absence of LVH and investigated the association of CABP and BABP with LVH. Summary statistics for normally distributed quantitative variables were expressed as means and standard deviations. For non-normally distributed variables, we used median and interquartile ranges; categorical data were summarized by ratios and percentages. Differences between the LVH and control groups regarding continuous variables with normal distribution were compared using the independent Student’s t-test, while abnormally distributed continuous variables were compared using the Mann–Whitney unpaired test. Differences between groups were tested by chi-square statistics for proportions. Participants were categorized in quartiles according to blood pressure measurements, setting the first quartile as the reference group. The analysis of variance (ANOVA) or chi-squared tests were used to compare the covariates of CABP quartiles. Correlations between continuous variables were assessed using the Spearman correlation coefficient. Multivariate logistic regression analysis was used to identify predictors of LVH and their corresponding odds ratio (OR) and 95% confidence intervals (95% CI). Receiver operating characteristic (ROC) curves were used to evaluate the accuracy of CABP and BABP to predict LVH. Statistical significance was defined as P < 0.05 for all tests; all P-values were two-sided. Statistical analyses were performed using the Statistical Package for the Social Sciences (IBM Corp, Released 2016, IBM SPSS Statistics for Windows, version 24.0, Armonk, NY: IBM Corp, USA) , Prism® (version 8.0, GraphPad, San Diego, CA, USA) and MedCalc (version 19.1, MedCalc Software, Ostend, Belgium).