Brain blood flow secrets revealed by breathing test

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: 1. Healthy adult subjects (\>18 years old) OR adult patients (\>18 years old) diagnosed with vascular pathology of the brain willing to participate and sign a consent form. 2. Able to participate in MRI scan without sedation 3. Not on stimulant medications 4. No psychiatric history, as defined by seeing a psychiatrist for medical evaluation and treatment, or taking anti-depressant medications 5. No seizure history 6. May have occasional headaches if not taking a daily preventative medication for headaches 7. Not on vasodilatory medication, such as sildenafil or verapamil Exclusion Criteria: 1. Subjects refusing to undergo testing 2. Subjects with obstructive or resistive lung disease whose PaCO2 at rest is greater than 50mmHg or whose venous serum bicarbonate is greater than 26 mEq/L 3. Subjects with pre-existing respiratory or metabolic acidosis 4. Subjects who require portable oxygen at rest or with exercise 5. Subjects with chronic heart failure or severe pulmonary disease who are unable to climb one flight of stairs due to shortness of breath 6. Subjects with severe heart failure or restrictive lung disease with resting respiratory rate over 15 breaths/min 2. Patients that cannot participate in a course of rehabilitation therapy. 7. Subjects that cannot undergo an MRI scan due to one of the following indications: * Pregnancy * Obtundation, or Coma * Confusion, Delirium, or Dementia * Unable to understand or carry out commands regarding keeping still and breathing pattern * Increased intracranial pressure due to space occupying lesion or obstruction of outflow of CSF * Claustrophobia * History of kidney problems * Pace makers * Skin tattoos * Neurostimulators (TENS-unit) * Implanted drug infusion device (i.e., insulin pump) * Exposure of metal fragments to your eye * Artificial heart valves * Aneurysm clips * Cochlear implants * Metallic implants and prosthesis * Vascular stent or stent graft * History as a metal worker * Shrapnel or bullet wounds * Dorsal column stimulators