Impaired hypoxic cerebral vasodilation in younger adults with metabolic syndrome

Metabolic syndrome (MetSyn) increases the risk of cerebrovascular disease and stroke; however, its impact on human cerebral circulation remains unclear. Reduced cerebral dilation is also associated with an increased risk of stroke and may occur in MetSyn adults. We hypothesised that MetSyn adults would exhibit reduced cerebral vasodilation to hypoxia and hypercapnia. Middle cerebral artery velocity (MCAv) was insonated with Doppler ultrasound in younger (approximately 35 years) MetSyn and healthy adults. We measured mean arterial blood pressure (MABP), arterial oxygen saturation (SpO2) and end tidal carbon dioxide (PETCO2). Cerebrovascular conductance index (CVCi) was calculated as MCAv* 100/MABP. Cerebral vasodilation (Delta CVCi) to hypoxia (SpO2 = 90% and 80%) and hypercapnia (+10 mm Hg PETCO2) was assessed. Baseline MCAv was similar, while adults with MetSyn had lower baseline CVCi. MetSyn adults demonstrated markedly reduced Delta CVCi compared to healthy adults in response to hypoxia (90% SpO2: 1 +/- 2 vs 6 +/- 2; 80% SpO2: 5 +/- 2 vs 15 +/- 3 cm/s/mmHg, p<0.05). Both groups demonstrated similar Delta CVCi to hypercapnia (18 +/- 2 vs 20 +/- 2 cm/s/mmHg). These data are the first to demonstrate that younger MetSyn adults have impaired hypoxia-mediated cerebral vasodilation prior to clinically overt cerebrovascular disease. These findings provide novel insight into cerebrovascular disease onset in MetSyn adults.