Study Populations

This study comprised 364 consecutive patients with established CVD or risk equivalent, recruited from our outpatient medical clinic. Established CVD included prior coronary artery disease and ischemic stroke, while CVD risk equivalence refers to conditions which confer equivalent cardiovascular risk and in our study context included patients with type II diabetes mellitus but without prior CAD/ ischemic stroke. Inclusion criteria constitute a homogeneous sample of subjects with presence of established coronary disease or factors considered to be of equivalent risks (i.e. ischemic stroke or diabetes mellitus) which place subjects at the medium to advanced spectrum of the cardiovascular continuum [7]. Diagnosis of coronary artery disease was established in the presence of any of the following: a history of myocardial infarction; a history suggestive of angina pectoris objectively evidenced by inducible ischemia on exercise treadmill or SPECT; and the presence of coronary atherosclerosis as defined by coronary angiography, computed tomography or magnetic resonance imaging. Diagnosis of ischemic stroke was made on the basis of clinical examinations and computed tomography brain imaging. Patients with type II DM were defined by WHO criteria [10]. Exclusion criteria constituted presence of non-conventional or non-cardiovascular factors which may present important confounding effects that may result in biased estimates of the relations under study or that may cause temporary potential fluctuations in vascular function parameters. These included dilated cardiomyopathy, pregnancy, history of heart failure, significant valvular heart disease, chronic atrial fibrillation, renal failure (serum creatinine > 1.2 mg/dL), cancer, recent myocardial infarction, unstable angina, or coronary revascularization within the past 6 months

During the study period, 93 age- and sex-matched healthy Chinese controls free from history of CVD or diabetes were recruited from a community health screening programme for comparison. The study was approved by the local ethics committee, the Institutional Review Board (IRB) of the University of Hong Kong/ Hospital Authority Hong Kong West Cluster (IRB, HKU/HA HKW Cluster). All participants understood and signed informed consent forms.

Demographic and clinical assessment

Demographic and clinical data were collected by an interviewer-administered structured questionnaire. Cardiovascular risk factors including tobacco smoking, hypercholesterolemia, hypertension, family history of CVD diagnosed in first-degree relatives before 55 years of age were assessed. Use of cardiovascular medications was recorded. Anthropometric measurements including body weight, height, and waist-hip circumferences ratio were measured. Body mass index (BMI) was then calculated in kg/m [2]. Systolic and diastolic blood pressures were measured. Fasting venous blood sample was obtained from all patients to measure serum glucose, HbA1c, triglyceride, total cholesterol, LDL-C and HDL-C levels.

Dietary assessment

A validated food frequency questionnaire (FFQ) for Chinese were used to assess dietary intake of all subjects over the past 6 months prior to date of interview, as described previously [11–13]. Briefly, subjects were assessed for frequency (day/week/month/year) and amount (unit of intake: liangs, equivalent to 37.8 g) intake of particular food past year, and 72 major food groups were recorded in FFQ. Types of fruit assessed included apples, pears, tangerines/oranges/grapefruits, bananas, grapes, watermelon, peaches and other fruits. Pictures of food with household units were shown to subjects to increase the accuracy of record. The conversion of dietary nutrients was performed by custom-made software as used in the Shanghai Women’s health Study [12]. High Carbohydrate diet was defined as daily carbohydrate intake of ≥60% of total energy, i.e. above the daily recommended intake (DRI) of carbohydrate at 60% of total energy (Chinese Nutrition Society) [14].

Arterial Stiffness

Arterial stiffness was measured non-invasively using Vascular Profiling System VP-2000 (Colin Corp., USA). All measurements were performed by a single experienced operator. Patients were allowed to rest in the supine position for 5 minutes in a quiet room before examination. Initially, the sites of maximum carotid and posterior popliteal arteries pulsation were determined by physical examination. Sequential recordings of pressure wave-forms at the precordium and the posterior popliteal arteries were made using hand-held manometer probes with simultaneous electrocardiogram gating. Measurement was taken after achieving coherent reproduction of signals with maximum amplitudes. Heart-ankle pulse wave velocity (PWV) was defined as the distance between the 2 points of measurement over the precordium and the respective posterior popliteal artery, divided by pulse transit time between the systolic R-wave and the upstroke of waveform at the posterior popliteal artery, and was calculated using system software with R-wave synchronisation over at least 10 cardiac cycles. A final estimate was derived from the average of the values from the bilateral measurements. Intra-observer variability testing revealed an intra-class correlation coefficient (two-way mixed, random-effect model, absolute agreement) of 0.87 (95% CI: 0.80 to 0.91, P < 0.001) for PWV measurement.

Statistical Methods

Continuous variables are expressed as mean ± SDs, and categorical data are presented as frequency and percentages. Statistical comparisons were performed by using Student’s t test, Pearson’s χ2 test, or the Fisher’s exact test, as appropriate. Absolute changes and 95% CIs of PWV were calculated by using univariate and multivariate linear regression analysis. Multivariate analyses were performed such that potentially confounding variables and known variables involved in prediction of PWV were chosen, including use of antihypertensive medications and statin [15, 16]. Each independent variable was considered a potential confounder if the p-value was <0.20 based on univariate analysis, and was entered and adjusted for in the multivariate Model. Multivariate linear regression analysis was repeated using the overall sample including all subjects, as well as separately among patients with CVD risk equivalent versus healthy controls. In the Full Model, all independent variables were entered and adjusted for all (Table 1). All data analyses were performed using the Statistical Package for the Social Sciences (version 16.0, SPSS). A value of P value less than 0.05 was considered statistically significant.