Does insulin resistance alter pulse transit time in the cerebral circulation?

Abstract

Approximately 80 million adults in the United States suffer from an insulin resistant state known as metabolic syndrome (MetSyn), associated with increased risk for strokes, cerebral infarcts and neurologic disease. Adults with MetSyn also exhibit increased peripheral arterial stiffness, but whether arterial stiffness occurs in the cerebral circulation remains unclear. We hypothesized adults with MetSyn would exhibit increased cerebrovascular stiffness, demonstrated as faster pulse transit time (PTT) compared to healthy adults. Participants were 32±7 years old, sedentary, non‐smoking, free of cardiovascular disease and unmedicated. Healthy normal‐weight adults (Control; n=11; weight=70±8 kg; BMI = 23±2 kg/m2) were normotensive and normolipidemic. Adults with MetSyn (n=6; BMI=38±8 kg/m2) met three or more of the five criteria according to American Diabetes Association (MAP=107±5 mmHg; glucose=82±17 mg/dL; triglycerides 167±123 mg/dL; HDL 39±9 mg/dL; waist circumference 119±16 cm). Subjects were instrumented to continuously monitor heart rate, blood pressure, and end‐tidal CO2. A 3T MRI using 4‐dimensional flow phase contrast vastly under‐sampled isotropic projection reconstruction (PC VIPR; ~6 minutes) was used to capture cerebral blood flow (CBF = blood velocity • vessel cross sectional area) in the internal carotid arteries (ICA) and superior sagittal sinus (SSS). Cerebral blood flow across 20 equal segments of the average cardiac cycle was used to determine the time to peak flow in the ICAs and SSS. Pulse transit time (PTT) was calculated as the difference in time to peak in the SSS from the time to peak in the ICAs. Data are presented as mean ± SD. Significance was determined using independent t‐tests and was set at p≤0.05. MAP, HR, SpO2, and end tidal CO2 were not different in magnet bore (p>0.05). ICA to SSS PTT was not different between Control and MetSyn (141±109 vs. 144±91 ms; p=0.743).ConclusionPulse transit time was similar between healthy adults and those with MetSyn. Perhaps greater disease severity, aging, or their combination are required to negatively change PTT in MetSyn. Alternatively, the cerebral circulation may be resistant to vascular stiffening.Support or Funding InformationADA 1‐12‐IN‐39