title: South Asians have adverse cerebrovascular haemodynamics, despite equivalent blood pressure, compared with Europeans. This is due to their greater hyperglycaemia.
abstract: BACKGROUND
  South Asians have a 1.5-fold increased stroke mortality compared with Europeans, despite similar blood pressures (BP). We hypothesized that it is the greater hyperglycaemia in South Asians that increases stroke risk, by adversely affecting cerebrovascular haemodynamics.
  
  
  METHODS
  A population-based sample of 149 Europeans and 151 South Asians underwent metabolic profiling and concurrent measurement of finger BP using a Finapres and middle cerebral artery (MCA) blood flow velocity using transcranial Doppler ultrasound. Cerebrovascular autoregulation, cerebrovascular resistance [resistive index (RI) and pulsatility index (PI)] were calculated. Means of cerebrovascular haemodynamic measures were compared by ethnicity, with the introduction of explanatory variables to a regression model to determine which variable could best account for ethnic differences.
  
  
  RESULTS
  Cerebrovascular resistance (RI) was 12.9 × 10(3) (0.9-24.8, P = 0.04) greater in South Asians than Europeans. Systolic, diastolic and mean MCA velocities were also higher in South Asians (mean velocity 41.4 ± 8.0 cm/s vs 38.0 ± 8.0 cm/s, respectively, P = 0.001). Low frequency gain, a measure of autoregulation, was worse in South Asians compared with Europeans (0.50 ± 0.01 cm/s mm/Hg vs 0.45 ± 0.01 cm/s mm/Hg, P = 0.01). RI positively correlated with HbA(1c) (r = 0.184; P < 0.01). Adjustment for BP could not explain the higher RI in South Asians, but adjustment for HbA(1c) abolished the ethnic difference in RI (5.8 × 10(3) (-6.5 to 18.1, P = 0.4).
  
  
  CONCLUSIONS
  Cerebrovascular resistance and autoregulation are worse in South Asians than in Europeans, despite equivalent resting BP. The greater hyperglycaemia in South Asians accounts for their adverse cerebrovascular resistance. This could explain excess stroke in South Asians but requires testing in longitudinal studies.
authors: National Heart and Lung Institute, Imperial College Academic Health Sciences Centre, London, UK.
authors: Rajaram
authors: R
authors: Bathula
authors: Alun D
authors: AD
authors: Hughes
authors: Ronney B
authors: RB
authors: Panerai
authors: John F
authors: JF
authors: Potter
authors: Simon A
authors: SA
authors: McG Thom
authors: Therese
authors: T
authors: Tillin
authors: Angela C
authors: AC
authors: Shore
authors: Rachel
authors: R
authors: Hale
authors: John
authors: J
authors: Chambers
authors: Jaspal
authors: J
authors: Kooner
authors: Nish
authors: N
authors: Chaturvedi
mesh_terms: D000328:Adult; D000368:Aged; D001211:Asia, Western / Q000453:epidemiology; D001794:Blood Pressure; D001921:Brain / Q000098:blood supply*; D005060:Europe; D005260:Female; D006439:Hemodynamics; D006801:Humans; D006943:Hyperglycemia / Q000150:complications / Q000208:ethnology*; D008297:Male; D008875:Middle Aged; D020521:Stroke / Q000097:blood / Q000150:complications / Q000208:ethnology*