Impaired post-ischaemic microvascular hyperaemia in Indian Asians is unexplained by diabetes or other cardiovascular risk factors.

OBJECTIVE: People of Indian Asian descent have an increased risk of cardiovascular disease (CVD) that cannot be explained by diabetes and other established CVD risk factors. We investigated if microcirculatory function was impaired in a population-based sample of people of Indian Asian descent compared with Europeans in the UK and whether any differences could be accounted for by diabetes or other CVD risk factors. RESEARCH DESIGN AND METHODS: Cutaneous microvascular function was assessed using laser Doppler fluximetry in response to heating to 42 °C (maximum hyperaemia) and 3 min arterial occlusion (post occlusive reactive hyperaemia: PORH) in 148 Indian Asians and 147 Europeans. Blood pressure, anthropometry and fasting bloods were also measured. RESULTS: Maximum hyperaemia and minimum resistance did not differ significantly by ethnicity. Resting flux and PORH were lower in Indian Asians and time to peak of PORH was prolonged. Diabetes was associated with reduced maximum hyperaemia and PORH. Adjustment for diabetes accounted for differences in resting flux and time to peak but not differences in PORH (Europeans = 45.0 (40.3, 50.1)au, Indian Asians = 35.6 (31.9, 39.7)au, mean (95% confidence interval); p = 0.008 after adjustment). Differences in conventional CVD risk factors did not account for interethnic differences in microvascular responses. CONCLUSIONS: People of Indian Asian descent have impaired post-occlusive reactive hyperaemia unexplained by diabetes, dysglycaemia or other CVD risk factors. Abnormal microvascular function in response to ischaemia could represent a novel mechanism contributing to the elevated risk of CVD in Indian Asians.

Indian Asians have poorer cardiovascular autonomic function than Europeans: this is due to greater hyperglycaemia and may contribute to their greater risk of heart disease.

AIMS/HYPOTHESIS: A high prevalence of diabetes contributes to excess CHD in Indian Asians, but the underlying mechanisms are unclear. Heart rate, heart rate variability (HRV) and baroreflex sensitivity (BRS) are measures of cardiac autonomic function that are disturbed by hyperglycaemia and predict CHD. We compared these measures in Indian Asians and Europeans, and sought explanations for the observed differences. METHODS: A representative sample of 149 Europeans and 151 Indian Asians was recruited from primary care, 66% of them men (aged 35-75 years), 34% women (aged 55-75 years). Heart rate, HRV, BRS and cardio-metabolic profiles were measured over four successive 5 min periods with continuous ECG and blood pressure monitoring. RESULTS: Indian Asians were hyperglycaemic compared with Europeans (HbA(1c) (mean +/- SD) 6.5 +/- 1.2% vs 5.9 +/- 1.0%, p = 0.001). They had shorter mean RR intervals ((mean +/- SE) 969 +/- 13 vs 1,022 +/- 12 ms, p = 0.002), lower total RR interval power ((geometric mean, 95% CI) 925 [796-1075] vs 1,224 [1,064-1,422] ms(2), p = 0.008) and lower BRS ((mean +/- SE) 5.7 +/- 1.0 vs 6.6 +/- 1.0 ms/mmHg, p = 0.01). All measures of cardiac autonomic dysfunction were significantly associated with hyperglycaemia (mean RR interval vs HbA(1c) r = -0.22; p < 0.001). Ethnic differences in cardiac autonomic function persisted after adjustment for age, blood pressure and medication (mean RR interval 973 vs 1,021 ms, p = 0.004), but were attenuated or abolished by adjusting for HbA(1c) (979 vs 1,014 ms, p = 0.06) or other markers of hyperglycaemia. CONCLUSIONS/INTERPRETATION: Indian Asians from the general population have impaired cardiovascular autonomic function compared with Europeans. This is due to greater hyperglycaemia in Indian Asians and may determine their increased CHD risk.