Doctors said there were several possible medical explanations for the incident on Sunday in which Bush apparently passed out after a pretzel went down the wrong way.

Dr. William Ravich said choking can cause a person to faint, an occurrence known as vasovagal syncope.

Pain, such as that caused by a cramp or choking, sends a signal to the vagus nerve, which in turns signals the heart, slowing it down so much that the person faints.

``It refers to a neurologically mediated fainting episode that is usually brought on by stress or pain,'' Ravich said in a telephone interview.

``It is something like when a person sees blood, he or she faints from the sight of blood,'' Ravich said. ``It is a stress-related response. ... If somebody felt he couldn't breathe, stress could cause you to lose consciousness. It would essentially lower blood pressure.''

If Bush coughed and coughed to get rid of the pretzel, he could also have fainted from that, Ravich said, simply having one's trachea blocked by food can also cause a faint.

``It is the type of thing the Heimlich maneuver is performed for,'' he said.

The Heimlich maneuver is a carefully placed push that can help dislodge an object from a choking person's throat.

``Choking can occur if a person is distracted,'' he said, ''Maybe presidents are more distracted than others,'' he added.

Choking can also be caused by a number of disorders, especially if the many muscles involved in swallowing do not work together.

So was grandma right when she advised chewing 30 times before swallowing? "Who would possibly count?'' Ravich asked. ``You swallow 600 times a day. Those are old wives tales. But you do want to chew your food and when people get in trouble is when they are not paying attention to chewing.''

Notes:
Pass out: lose consciousness; faint
Bring on: lead to, cause or result in something
Old wives' tale: old and usually foolish idea or belief

(Agencies)