Development of a Clinically-relevant Test for Assessment of Cerebral Vascular Function

Inclusion Criteria: Young and Older Healthy Adults: * Males and females willing and able to provide informed consent * Aged between 18-35 years (Young) or 60-80 years (Older) * Premenopausal women will be tested within 1-4 days after menses begins to control for hormone status * Women taking oral contraceptives will be allowed to participate and they will be tested in the low hormone or placebo phase * Postmenopausal women (at least 12 months since last menstrual cycle) who are not on hormone replacement therapy will be eligible * Sedentary or recreationally active * Non-tobacco/nicotine users (e.g., cigarettes, chewing tobacco, nicotine gum or patches) * Laboratory measured systolic blood pressure \<140 mmHg and diastolic blood pressure \<90 mmHg * Normal 12-lead ECG (reviewed by a physician) * Normal clinical results from a medical exam reviewed by a board certified physician (e.g., Medical \& Behavioral Health Questionnaire - see attached document) * Body mass index (BMI) \<40 kg/m2 unless athletic/muscular build; calculation = body weight (kg)/height (m2); this criteria is used to ensure subjects will fit inside the LBNP chamber * Females only: documentation of a negative pregnancy test prior to the familiarization and experimental sessions Young and Older Chronic Smokers of Tobacco Cigarettes: The same criteria (a-c and e-i above) as Young and Older Healthy Adults, except: \- Chronic smokers of tobacco cigarettes only (i.e., at least 20 pack year use) Exclusion Criteria: Young and Older Healthy Adults: * Age \<18 years, or 40-60 years, or \>80 years * Body mass index (BMI) \>40 kg/m2 unless athletic/muscular build; calculation = body weight (kg)/height (m2) * Regular tobacco/nicotine users within the last 6 months (e.g., cigarettes, chewing tobacco, nicotine gum or patches) * Not abstaining from the following 24 hours prior to the familiarization session and the experimental session: exercise, alcoholic substances, prescription or non-prescription medications (unless cleared by the medical screener), dietary supplements, herbal medications, caffeinated substances (including coffee, tea (iced or hot), caffeinated energy drinks or sodas). * Not fasted for at least 3-4 hours prior to the experimental sessions. * Positive pregnancy test * Hormone replacement therapy (males and females) * Females with an erratic/irregular menstrual cycle * Females who are using a continually-releasing hormonal (e.g., NuvaRing™ or other hormone-releasing vaginal rings, Depo Provera shot, birth control implants such as Nexplanon) and who do not have a regular menstrual cycle * Use of prescription drugs, non-prescription drugs or herbal medicines known to alter autonomic function unless cleared prior to the study * Any metabolic disease, except individuals who are on cholesterol-lowering medications (older subjects only; young subjects on cholesterol-lowering medications will be excluded) * Use of two or more anti-hypertensive medications (older subjects only; young subjects on anti-hypertensive medications will be excluded) * Use of beta blockers * Frequent use of bronchodilators * Use of anti-coagulant therapy * Current or past history of hyperthyroidism, or other thyroid hormone-related disease * Signs of cardiovascular abnormalities (e.g., resting systolic blood pressure \>140 mmHg or diastolic blood pressure \>90 mmHg; abnormal 12-lead ECG) * History of cerebrovascular abnormalities (e.g., prior stroke, transient ischemic attacks, epilepsy) * Known history of atherosclerosis of the carotid arteries (i.e., plaque formation) * Known history of peripheral artery disease (PAD) * Concussion and or other loss of consciousness within the past 30 days. * Autonomic dysfunction (e.g., Shy-Drager Syndrome, Bradbury-Eggleston syndrome, sinus arrhythmia, idiopathic orthostatic hypotension, fainting disorder) * Respiratory illnesses (e.g., chronic asthma (including exercise-induced asthma), Chronic Obstructive Pulmonary Disease, Reactive Airway Disease) * History of anaphylaxis * History of pre-syncopal/syncopal episodes or orthostatic hypotension * Donated blood within the last 60 days * History or family history of abnormal blood clotting, clots in deep veins in the legs or pelvis, or blood clots to the lungs * Known or suspected abdominal hernia * History of alcohol or drug abuse which inhibits the subject's ability to complete this study * Known depression, anxiety, or any other mental health issue which inhibits the subject's ability to complete this study Young and Older Chronic Smokers of Tobacco Cigarettes The same criteria (a-b and d-dd above) as Young and Older Healthy Adults, except: \- Less than 20 pack year use of tobacco cigarettes, or regular use of other tobacco/nicotine products within the last 6 months (e.g., electronic cigarettes, chewing tobacco, nicotine gum or patches).