UTLight-transcranial Doppler Assessment of Regional Cerebral Autoregulation

Cerebral autoregulation (CA) is a complex mechanism that serves the essential and vital purpose of controlling cerebral blood flow and metabolism. A stable and optimal brain blood flow is imperative for normal brain function. Diabetes Mellitus (DM ) is associated with microvascular disease that alters CA and also with autonomic failure that may lead to orthostatic hypotension (OH). These conditions may lead to decreased brain blood flow in upright position. This observational study will compare two technologies that evaluate brain blood flow during standing up and other maneuvers in people with and without type 2 diabetes. These technologies are transcranial Doppler and UTLight technology (CerOx). This study will determine the safety and feasibility of CerOx technology for continuous monitoring of cerebral blood flow.

Cerebral autoregulation (CA) is a complex mechanism that serves the essential and vital purpose of controlling cerebral blood flow and metabolism. A stable and optimal brain blood flow is imperative for normal brain function; therefore normal function of CA is crucial for brain health. Diabetes mellitus (DM) is associated with microvascular disease and abnormal autoregulation, which increases risk for stroke and death. Failure of CA has serious consequences across the lifespan and, in terms of prevalence adverse outcomes related to failing CA are most prominent in the elderly with diabetes. Older diabetic adults often suffer from hypotension or fainting upon standing-up and may have abnormal CA. With abnormal CA, cerebral perfusion and tissue oxygenation declines upon standing up. Abnormalities in perfusion regulation in older people, and particularly those with diabetes may accelerate progression of brain atrophy resulting in cognitive decline, vascular dementia or Alzheimer's disease. UTLight technology (CerOx), provides a new tool for evaluation of regional blood flow and oxygenation in cortical microvasculature, which is lacking in clinical medicine and patient care. UTLight may become a novel tool that would provide an easy and reliable assessment of regional perfusion and CA in specific cortical areas in health and disease that can be widely implemented in outpatient clinics. This is a pilot, observational feasibility study to compare blood flow measurements using UTLight and TCD. Aim 1: To assess the safety and feasibility of UTLight for evaluation of regional cerebral blood flow regulation in the anterior circulation ((ACA) and/or middle cerebral artery (MCA) territories) in 20 non-diabetic adults \>50 yrs old and 40 age-matched adults with type 2 diabetes. Aim 2: To compare the profiles of UTLight blood flow (UT\_BF), regional oximetry (UT\_Ox) and TCD-blood flow velocities (TCD\_BFV) in response to: 1) blood pressure changes induced by the postural change from supine to head-up tilt, and from sitting to standing-up; and 2) vasodilatation and vasoconstriction responses induced by hypercapnia and hypocapnia. The investigators hypothesize that: 1. UT\_BF will accurately track TCD\_BFV in responses in the anterior circulation (ACA and/or MCA territory) to blood pressure changes, hypercapnia and hypocapnia challenges in healthy older people. 2. UT\_BF may be more sensitive to detect abnormalities in regional perfusion in diabetic adults as compared to healthy controls and compared to TCD\_BFV. (UT\_Ox) may provide a new indicator to identify older diabetic adults with brain tissue hypoxia during orthostatic challenges that may be at greater risk of brain damage of cognitive decline that will be derived from a change in tissue oxygenation upon standing up that is not routinely evaluated by TCD. Outcomes: Primary outcome is the sensitivity and specificity of UT\_BF and TCD\_BFV to blood pressure and CO2 challenges, defined as percent change of UT\_BF and TCD\_BFV in response to hypercapnia and hypocapnia challenges. Secondary outcomes are the differences in cerebral blood flow measured by UT\_BF, TCD\_BFV between healthy old and diabetic subjects during postural changes. Third outcomes are differences in UT\_Ox between healthy old and diabetic subjects.