Brain Blood Vessel Responses to Changes in Blood Flow: Younger Cohort

Exclusion Criteria15

• Diagnosis of Mild Cognitive Impairment (MCI) or Alzheimer's disease (AD)
• History or evidence of hepatic disease, hematological disease, or peripheral vascular disease; severe kidney injury requiring hemodialysis
• History of cardiovascular disease including: severe congestive heart failure, coronary artery disease, ischemic heart disease (stents, coronary artery bypass grafts) and tachycardia
• Uncontrolled hypertension
• History of clinically significant ischemic or hemorrhagic stroke, or significant cerebrovascular disease
• Severe untreated obstructive sleep apnea
• History of diabetes with HbA1c greater than 9.5 percent
• Major neurologic disorders other than dementia (e.g., MS, ALS, brain surgery, etc.)
• Current or recent (less than1 year) major psychiatric condition (Axis I) or addictive disorders
• Significant surgical history
• Other significant medical conditions at investigators' discretion
• Contraindications to MRI
• Prescribed medications that interfere with prazosin
• Lactose allergy
• lower body will not fit in lower body negative pressure (LBNP) chamber (regardless of overall height and BMI)