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Don't perform the Heimlich maneuver on a person who is choking but can still speak.

Each year, 3,000–4,000 Americans die from choking, or pulmonary aspiration — about the same as the number who die by drowning. Choking happens mainly during meals, and meat is the chief culprit. But food and small objects aren't the only causes. Swelling from a severe allergic reaction — or in an unconscious person, the tongue — can prevent air from flowing into the lungs.

Shared commute

Things go down the wrong way and cause us to choke because of an anatomical flaw that we share with most other air-breathing vertebrates. Our breathing tube, the windpipe or trachea, isn't segregated from the one we use for swallowing, the esophagus. Air, food, and drink all share the same commute down the throat until the trachea branches off, right around your Adam's apple.

Normally, the epiglottis keeps food and drink from going down the windpipe. This sturdy flap of cartilage is designed to snap shut automatically when we swallow, closing off the airway and shunting the sustenance down the esophagus to meet its digestive fate.

Another automatic body function, the gag reflex, sometimes keeps unwanted objects out of the upper respiratory tract by triggering a reverse contraction of throat muscles. We gag for many reasons; sometimes it's just a matter of tissues in the throat getting irritated. Gagging can feel like choking, but it's not the same. In fact, the gag reflex can prevent choking by clearing the throat of an unwanted substance.

Who's at risk?

Choking is most likely to occur in very young children, particularly toddlers, and in the elderly. Toddlers, those wonderfully curious creatures, like to explore their surroundings with their mouths — which often means putting things in them. If you've ever shopped for a toy for a young child, you've probably seen the choking hazard warning on items with small pieces.

Older people are vulnerable because they lose some of the reflexes and muscle tone needed to eject an object from the trachea. A condition like Parkinson's disease makes an older person even more vulnerable. Cognitive disorders like Alzheimer's disease can lead to swallowing difficulties and a greater likelihood of choking.

Drinking can be a contributing factor because alcohol suppresses the airway's protective reflexes.

Signs of choking

Choking on a bite of food used to be called a "café coronary" because it often occurred in restaurants and was mistaken for a heart attack. But once you know the signs of choking, they're easy to spot even without medical training. They include

• grabbing at the throat

• difficulty speaking

• weak, ineffective cough or labored breathing, sometimes accompanied by wheezing or whistling

• face turning blue from lack of oxygen (cyanosis).

When you see someone choking, speed is of the essence. Without adequate oxygen, the person will quickly lose consciousness and could suffer permanent brain damage in as little as four to five minutes.

What should you do?

First ask him or her, "Are you choking?" If the person indicates yes, then ask in a calm voice, "Can you speak?"

Don't perform the Heimlich maneuver on anyone who's able to talk. "If a person can speak, there isn't a major obstruction and the airway is at least partially intact," says Dr. Toby Nagurney, an emergency department physician at Massachusetts General Hospital. In this situation, encourage the person to continue breathing and to cough forcefully, which is the best way to dislodge items stuck in the airway. Stay with the person until he or she feels better or medically trained personnel have arrived. If someone is vomiting or seems to be losing consciousness then you should lay the person on his or her side. An upright position could be dangerous because an object that is partially blocking the trachea could be pulled further into it, creating a complete obstruction, notes Dr. Nagurney.

If the person can't talk, then you should try the Heimlich maneuver while having someone call 911 for help. We've posted more information about the maneuver on our Web site at /healthextra.