Former president Richard Nixon's condition was downgraded to critical Wednesday after brain swelling was detected following a major stroke.
"His prognosis is guarded. These are critical hours," said Fred Plum, one of Nixon's doctors at New York Hospital-Cornell Medical Center.
Nixon, 81, was awake and alert when first hospitalized Monday after a stroke at his suburban New Jersey home.
He was moved out of intensive care Tuesday but moved back in after he began to fall in and out of consciousness.
Nixon, who became the first president to resign office in the wake of the Watergate scandal in 1974, received hundreds of get-well messages from around the world Wednesday, including a telegram from Russian President Boris Yeltsin.
According to doctors, Nixon has been treated for several years for an irregular heartbeat, which increases the risk of blood clots and raises susceptibility to an occlusive stroke, the most common form.
An occlusive stroke occurs when a blood vessel in the brain is blocked.
The other form of stroke, hemorrhagic, occurs when a blood vessel ruptures.
Experts say Nixon's stroke appears to have affected a portion of the left side of the brain, and based on information released by the hospital, his prognosis could be poor.
He is paralyzed on the right side of his body, able to move his right foot only slightly, and he cannot speak.
A stroke on the left side of the brain affects the speech expression center. The center connected to understanding speech is in another area.
Brain swelling often follows a more severe occlusive stroke, says neurosurgeon Laligam Sekhar of George Washington University. Sekhar treated Vice President Gore's mother, Pauline, for a stroke several months ago.
"When a person has a massive stroke, they may suffer severe brain swelling and die," Sekhar says. "If it's a small stroke, the vessels around the brain can resupply blood flow and allow recovery."
Swelling occurs as brain cells die and as the barrier between brain cells and blood vessels deteriorates.
Both problems allow fluid to build in the tissue. As swelling increases, pressure on the brain stem may affect the body's most basic functions.
Rehabilitation is tied directly to the seriousness of the stroke rather than age or the underlying disease.
People who suffer strokes that affect smaller blood vessels in less critical brain areas are the most easily rehabilitated, University of Cincinnati neurologist Joe Broderick says.
Strokes are the leading cause of disability in adults. Warning signs:
-- Numbness or weakness in the face, arm or leg.
-- Difficulty speaking or understanding.
-- Dizziness accompanied by one or more warning signs.
-- Sudden blurred or decreased vision.
Risk factors include heart disease, diabetes, high blood pressure, smoking, heavy drinking or obesity. Also, older people, men and blacks have an increased risk.
Nixon's serious stroke
An occlusive stroke, such as the one President Nixon suffered, is the most common form of stroke. About 500,000 Americans have strokes each year. More that 140,000 die. How occlusive stroke occurs:
1. Blood clot breaks away from heart or artery, blocks left side of brain. Left side of brain generally controls right side of body and speech. Effect: Nixon's right side is paralyzed. He able to move his right foot only slightly and is unable to speak.
2. Brain swelling occurs as cells, cut off from regular blood flow, die and as barrier between brain cells and blood vessels deteriorates. Both problems allow fluid to build in the tissue. Effect: As swelling becomes more severe, person becomes drowsy, loses consciousness.
Treatment Neurologist Joe Broderick of the Greater Cincinnati/Northern Kentucky Stroke Team at the University of Cincinnati, says there is no proven treatment for brain swelling caused by stroke. "There is only so much space in the skull and if you have a lot of swelling, it pushes on other parts of the brain, including deep areas. That can cause more problems than just stroke itself."
