Study design
The Northern Shanghai Study is a prospective, on-going and multistage study, and aims to investigate the CV risk assessment system in the elderly Chinese, as previously described [13, 14].We recruited residents from urban communities in the north of Shanghai (aged 65 years or more), who are also available for long-term follow-up. Subjects with severe cardiac disease (NYHA IV) or end-stage renal disease (CKD > 4), or malignant tumor with life expectancy less than 5 years, or stroke history within 3 months were excluded. Finally, 2830 participants (91.5%) were enrolled from June 2014 to May 2018. The study was approved by the Ethics Committee of Shanghai Tenth People’s Hospital, and written informed consent was obtained from all participants.
Definition of weekly walking activity
Weekly walking activity was evaluated by standard questionnaire based on the International Physical Activity Questionnaires-short form (including how many days spent on walking at least 10 minutes at a time and walking duration time) [15, 16]. In subgroup analysis, walking duration per day was classified into two categories: over 30 min/day and over 1 h/day, and walking days per week were categorized into < 4 and ≥ 4 days/week.
Social, clinical and biological parameters
We obtained social and clinical information from standard questionnaire, including gender, age, weight, smoking habits, history of hypertension / diabetes mellitus / coronary heart diseases, and usage of medications, etc [13].
As to biological markers, venous blood samples and urine samples were obtained from subjects after an overnight fast. Biological markers were measured in the Department of Laboratory Medicine of Shanghai Tenth People's Hospital, including fasting plasma glucose, plasma low-density lipoprotein (LDL) cholesterol, high-density lipoprotein (HDL) cholesterol, plasma creatinine, urinary microalbumin and creatinine, etc. We respectively calculated creatinine clearance rate (CCR) and urinary albumin-creatinine ratio (UACR) based on the modified MDRD formula for Chinese and urinary microalbumin divided by urinary creatinine [14].
Measurement of blood pressure, ankle-brachial index and carotid-femoral pulse wave velocity
Specialized physicians measured the blood pressure (BP) of each subject in the morning by the electronic device three times after at least 10 minutes of rest in the sitting position. The average of the three BP readings was used in the subsequent statistical analysis.
Bilateral brachial and ankle blood pressures were measured and ankle-brachial index (ABI, calculated as ankle systolic BP divided by brachial systolic BP) was automatically calculated via the VP1000 system (Omron, Japan). Lower ABI was used for analysis in the present study.
Carotid-femoral pulse wave velocity (Cf-PWV) was measured using SphygmoCor system (AtCor Medical, Australia) to assess the arterial stiffness. Briefly, after a 10-minute rest, peripheral BP was recorded twice with an interval of 3 minutes, and measurements of the superficial distance directly from the carotid to the femoral artery were performed. Subsequently, pressure waveforms in the right carotid and right femoral arteries were recorded, and transit time for each artery was automatically calculated via ECG data. Finally, cf-PWV was calculated by travelling distance divided by travelling time. An operator index greater than 80% indicated a high-quality waveform.
Ultrasonography
All ultrasonographic measurements were performed by a single experienced sonographer. Arterial plaque and common carotid artery intima-media thickness (CIMT) was assayed by the MyLab 30 Gold CV system (ESAOTE SpA, Genoa, Italy). The presence or absence of plaques in the left and right carotid arteries was recorded. CIMT was measured on the left common carotid artery (always on plaque-free arterial segments), 2 cm from the bifurcation, as previously described [14]. The average value of three CIMT measurements was used for further analysis.
Furthermore, M-mode and 2-dimensional echocardiography were performed using the same device, according to the guidelines of the American Society of Echocardiography (ASE). From the parasternal view, we measured left ventricular end-diastolic diameter (LVEDd), interventricular septal (IVSd) and posterior wall thickness at end-diastole (PWTd), and then calculated left ventricular mass index (LVMI). Simultaneously, peak transmitral pulsed Doppler velocity / early diastolic tissue Doppler velocity (E/Ea) was calculated for the evaluation of LV diastolic function. Additionally, left atrial volume index (LAVI) was calculated using model formula, as previously described [13].
Definition of asymptomatic hypertensive mediated organ damage
Asymptomatic HMOD included cardiac, renal and vascular HMOD. Left ventricular hypertrophy was defined as LVMI ≥ 115 g/m2 (male) or LVMI ≥ 95 g/m2 (female). LV diastolic dysfunction was defined as E/Ea ≥ 15, or 15 > E/Ea > 8 with any of the follows (LAVI > 40 ml/m2 or LVMI > 149 g/m2 (male) or LVMI ≥ 122 g/m2 (female)). Chronic kidney diseases (CCR < 60 ml/min/1.73m2) and microalbuminuria (UACR > 30) represented renal HMOD, while vascular HMOD included the presence of arterial plaque, increased CIMT (CIMT > 900 μm), arterial stiffness (cf-PWV ≥ 12 m/s) and peripheral artery disease (ABI < 0.9).
Statistical analysis
Data were presented as means ± standard deviation or the percentage by Student’s t-test or Chi-squared test, respectively. Pearson’s correlation analysis was applied to investigate the correlation of cardiovascular risk factors with walking activity. Logistic regressions were conducted to investigate the association of weekly walking activity with HMOD, together with cardiovascular risk factors. In subgroup analysis, pearson’s correlation analysis and logistic regressions were performed to investigate walking days per week and walking duration per day in association with vascular HMOD. Statistical analysis was performed using SAS software, version 9.3 (SAS Institute, Cary, NC, USA). P < 0.05 was considered statistically significant.