Impaired hypoxic cerebral vasodilation in younger adults with metabolic syndrome

Abstract

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 (S(p)O(2)) and end tidal carbon dioxide (Pet (CO2)). Cerebrovascular conductance index (CVCi) was calculated as MCAv*100/MABP. Cerebral vasodilation (ΔCVCi) to hypoxia (S(p)O(2) = 90% and 80%) and hypercapnia (+10 mm Hg Pet (CO2)) was assessed. Baseline MCAv was similar, while adults with MetSyn had lower baseline CVCi. MetSyn adults demonstrated markedly reduced ΔCVCi compared to healthy adults in response to hypoxia (90% S(p)O(2): 1±2 vs 6±2; 80% S(p)O(2): 5±2 vs 15±3 cm/s/mmHg, p<0.05). Both groups demonstrated similar ΔCVCi 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.

Figure 1

Isocapnic hypoxia. (A) Group mean CVCi – S_pO₂ values in metabolic syndrome (MetSyn) and healthy adults; (B) Group mean absolute ΔCVCi to 90% and 80% S_pO₂ ; (C) Individual subject and group mean stimulus-response slopes of CVCi at 90% and 80% S_pO₂ (a negative value reflects vasodilation). ΔCVCi : cerebral vasodilation; CVCi: cerebrovascular conductance index; S_pO₂: arterial oxygen saturation. All group data are presented as group mean ± SE. *Main effect of S_pO₂ 80% hypoxia on CVCi v. baseline (p<0.05). †Main effect of group (p<0.05). ‡Main effect of S_pO₂ 80% hypoxia vs S_pO₂ 90% (p<0.05).

Figure 2

Hyperoxic hypercapnia. (A) Group mean CVCi and Pet_CO2 values in metabolic syndrome (MetSyn) and healthy adults; (B) Absolute ΔCVCi group means (p=0.66); (C) Individual and group mean stimulus-response slopes (p=0.71, positive value reflects vasodilation). CVCi: cerebrovascular conductance index; Pet_CO2: end tidal carbon dioxide. All group data are presented as group mean ± SE. *Main effect of hypercapnia on CVCi (p<0.05). †Main effect of group (p<0.05).