This study will evaluate magnetic resonance imaging (MRI ) methods for measuring changes in
the brain's blood flow during hypercapnia (a condition of excess carbon dioxide in the
blood). MRI is a diagnostic tool that uses a large magnet and radio waves to produce images
of the body without X-rays.
Healthy normal volunteers in this study may have as many as six MRI scans over a 2-year
period. For this procedure, the person lies on a stretcher placed in a strong magnetic
field produced by the MRI machine. During the scan, the person's blood carbon dioxide (CO2
) levels will be increased either by: 1) breathing air mixtures containing up to 5% CO2; or
2) receiving an intravenous (I.V.) injection of a drug called acetazolamide.
Persons who breathe CO2 will have their heart rate, blood pressure and oxygen levels
monitored throughout the procedure. Those receiving acetazolamide will have the drug
injected intravenously (I.V.) into an arm vein. If the volunteer experiences any unpleasant
side effects from the CO2 or acetazolamide, the study will be stopped.
The information gained from this study will be used to develop better ways to study brain
function, possibly leading to better diagnostic and treatment methods.
Advances in MR perfusion imaging have provided clinical researchers with the opportunity to
quantitate regional increases in cerebral blood flow. The purpose of this study is to
acquire the technical experience required to perform MR perfusion imaging studies of the
hypercapnic cerebral blood flow response. Cerebral blood flow will be increased by
inhalation of carbogen (an air mixture containing 5% CO2) or IV injection of the carbonic
anhydrase inhibitor acetazolamide. The technical experience obtained in this study will be
used to design a study of the pharmacological and physiological mechanisms underlying
cerebral blood flow increases during hypercapnia.
Any normal volunteer above the age of 18 years old who is capable of giving informed
Subjects will be excluded if they have contraindications to MR scanning, such as the
following: aneurism clip, implanted neural stimulator, implanted cardiac pacemaker or
autodefibrillator, chochlear implant, ocular foreign body (e.g., metal shavings), or
insulin pump. Also, subjects will be excluded if they have panic disorder or migrane
(because of possible complications with CO2 inhilation), or if they have cirrhosis, are on
high dose aspirin therapy, or have an allergy to acetazolamide injection). Subjects will
be excluded if they have allergies to sulfonamide drugs or if they have a chronic