Background: Body mass index (BMI) and waist circumference (WC) correlate with cardiovascular (CV) risk factors in childhood which track into adulthood. WC provides a measure of central obesity, which has been specifically associated with CV risk factors. Reference standards for WC, and for WC and BMI risk threshold values are not established in Chinese children. Objectives: To construct reference percentile charts of WC, establish relationships between WC, BMI and other risk factors, and propose WC and BMI threshold values predictive of CV risk factors in Hong Kong ethnic Chinese children. Methods: Weight, height, waist and hip circumference were measured in 2593 (52% boys, 47% girls) randomly sampled Hong Kong school children aged 6-12 years. In 958 of these and 97 additional overweight children (n ¼ 1055), the relationships between WC, BMI, waist/hip and waist/height ratio and six age-adjusted CV risk factors (485% percentile levels of blood pressure (BP), fasting triglycerides, low-density lipoprotein (LDL) cholesterol, glucose and insulin levels, and o15% percentile levels of high-density lipoprotein (HDL) cholesterol) were studied. Receiver-operating characteristic analysis was employed to derive optimal age-adjusted sex-specific WC and BMI thresholds for predicting these measures of risk. Results: WC percentiles were constructed. WC correlated slightly more than BMI with CV risk factors and most strongly with insulin and systolic BP, but poorly or not with LDL and glucose. Optimal WC and BMI risk thresholds for predicting four of these six CV risk factors were ca. the 85th percentiles (sensitivities B0.8, specificities B0.87) with age-specific cutoff values in girls/ boys from B57/58 to B71/76 cm and 17/18 to 22/23 kg/m 2 . Conclusion: These are the first set of WC reference data for Chinese children. WC risk cutoff values are proposed which, despite a smaller waist in Chinese children, are similar to those reported for American children. WC percentiles may reflect population risk.

Background: Childhood obstructive sleep apnoea (OSA) is suggested to be associated with cardiac structural abnormalities and dysfunction but existing evidence is limited and the treatment effect on echocardiographic outcome remains controversial. Objective: To examine the presence of subclinical cardiac abnormalities in childhood OSA and the effects of treatment on cardiac changes. Methods: Polysomnography (PSG) and echocardiographic examinations were performed in 101 children aged between 6 and 13 years who were invited from a community based questionnaire survey. They were classified into a reference group (apnoea-hypopnoea index (AHI) ,1, n = 35), mild OSA group (AHI 1-5, n = 39) and moderate to severe group (AHI .5, n = 27) based on the PSG results. Treatments, including adenotonsillectomy or nasal steroids, were offered to the mild and moderate to severe OSA groups. Results: The moderate to severe OSA group had greater right ventricular (RV) systolic volume index (RVSVI), lower RV ejection fraction (RVEF) and higher RV myocardial performance index (RVMPI) than the reference group. They also had more significant left ventricular (LV) diastolic dysfunction and remodelling with larger interventricular septal thickness index (IVSI) and relative wall thickness than those with lower AHI values. The moderate to severe OSA group had an increased risk of abnormal LV geometry compared with the reference group (odds ratio 4.21 (95% CI 1.35 to 13.12)). Log transformed AHI was associated with RVSVI (p = 0.0002), RVEF (p = 0.0001) and RVMPI (p,0.0001), independent of the effect of obesity. Improvement in RVMPI, IVSI and E/e9 were observed in those with a significant reduction in AHI (.50%) comparing 6 month with baseline data. Conclusions: OSA is an independent risk factor for subclinical RV and LV dysfunction, and improvement in AHI is associated with reversibility of these abnormalities.Childhood obstructive sleep apnoea (OSA) is being increasingly recognised and its prevalence among the paediatric population is reported as 2-4%.

Elevated RHR is independently associated with elevated BP in children, whereas increased structured exercise is related to lower RHR.