Reduced Blood Flow Velocity Precedes Diabetic Microvascular Disease

A slowing of blood flow in the middle cerebral arteries, may signal the onset of microvascular disease in elderly patients with type 2 diabetes, a potential mechanism of cerebrovascular disease in these patients. Dr. Vera Novak, at Beth Israel Deaconess Medical Center in Boston, and associates studied blood flow in the brains of 28 type 2 diabetics and 23 controls. The mean age was 62.3 years.

The researchers used transcranial Doppler ultrasound at rest and during hyperventilation to reduce carbon dioxide to 25 mm Hg for 3 minutes to assess cerebral blood velocity. Measurements were taken again after breathing 5% carbon dioxide and 95% air for 3 minutes to increase carbon dioxide level to 45 mmHg. The investigators then compared changes on ultrasound with changes in white matter hyperintensity on MRI.

Compared with controls, diabetics had a lower mean blood flow velocity and higher cerebrovascular resistance at baseline, defined as mean blood pressure divided by mean cerebral blood flow velocity. Diabetics also had hypocapnia, hypercapnia and impaired carbon dioxide reactivity compared with controls.

Baseline blood flow velocity positively correlated with systolic blood pressure, but was negatively associated with periventricular white matter hyperintensity, hemoglobin A1c levels and the presence of inflammatory markers, Dr. Novak’s team reports in the July issue of Diabetes Care.

This study provides "further evidence that type 2 diabetics is associated with microvascular disease that may reduce cerebral blood flow in elderly people. Interventions to treat microvascular disease and to enhance cerebral blood flow may play a role in preventing cerebrovascular complications of diabetes," the researchers conclude.

The jury is still out on whether reduced cerebral blood flow is a cause or an effect of white matter disease, the investigators note.
Diabetes Care 206;29:1529-1534.

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