Q: When riding Metro, I sometimes develop sudden pressure in my ears, similar to that during airplane descents. Is this harmful to my eardrums?

A: As Metro trains speed through tunnels, they push and compress the air inside the tunnel. This causes a build-up of air pressure, which some riders feel against their eardrums. When the train passes an air vent or other opening that allows the air to escape, the pressure suddenly drops, causing some people's ears to "pop."

The pressures are probably less pronounced and shorter lasting than those you feel during airplane descents. It is very unlikely that this pressure damages normal eardrums.

You can relieve the ear pressure by holding your nose, closing your mouth and gently blowing against your pinched nose. This will send a small puff of air through the Eustachian tube, a tiny connection between the back of your nose and middle ear space in the inner side of your eardrum. This action equalizes the air pressure on both sides of your eardrum, restoring it to a normal position and feeling.

This maneuver also works well for ear pressure during airplane descents, but shouldn't be done if you have a cold or runny nose, because you may blow some bacteria into the middle ear space and cause an infection. It also shouldn't be done if you've ever had a perforation or hole in your eardrum, even if it's healed.

People with Eustachian tube problems are more likely to have trouble equalizing eardrum pressure. People with colds or allergies and those who smoke have Eustachian tubes that don't work as well as they should.

Q: What is the difference between cholesterol, triglycerides and hyperlipidemia? Would a low-cholesterol diet also reduce triglyceride levels in your blood?

A: Hyperlipidemia is a general term meaning increased amounts of fats in the blood (hyper means high, lipid means fat, and emia means blood). Hyperlipidemia and hyperlipoproteinemia refer to the same condition. Cholesterol and triglycerides are both lipids (fats), so hyperlipidemia could refer to increased amounts of either or both of these substances.

Fats in the blood aren't closely connected with being overweight -- thin people can have hyperlipidemia, too. Doctors have divided high blood fat levels into about six types, depending on the amounts and types of lipids in the blood.

Cholesterol is important because high levels of it in the blood are associated with high risk of heart disease and heart attacks. Cholesterol travels through the bloodstream attached to lipoproteins, combinations of lipids and protein. One type of lipoprotein, known as high-density lipoprotein (HDL), actually protects against heart disease and has been called the "good cholesterol."

Triglycerides are another type of lipid and aren't as important as cholestrol with regard to heart disease. Extremely high levels may cause painful inflammation of the pancreas (pancreatitis), but this happens infrequently.

A diet low in cholesterol and saturated fat helps most types of hyperlipidemias, including high triglyceride levels. Weight reduction, if needed, is also usually helpful, and in some cases cutting back on alcoholic beverages is, too. If diet alone doesn't work, a variety of medications are effective in lowering lipid levels.

Q: My 2-year-old terror gets into everything that isn't nailed shut. Last week I caught him playing with the laundry soap. What can I do to prevent accidental poisoning?

A: It's impossible to prevent every accident your son can have, but here are some tips for "poison-proofing" your home:

Store all harmful substances out of your child's reach or in cabinets with child-resistant locks. But don't underestimate your child's ability to reach places that seem unreachable.

Keep all medicines in bottles with child-resistant caps, and try to buy household products with these types of tops.

Most accidental ingestions occur while the product is being used, so keep a careful eye on your child while working with, say, your household bleach. If you leave the room to answer the phone, take the product or your child with you.

Be extremely conscientious about the most dangerous, potentially lethal products, such as drain cleaner, windshield washer fluid, antifreeze, insecticides, gasoline, kerosene and paint thinner.

Also keep in mind commonly overlooked sources of toxic ingestions, such as certain plants and cigarettes, and places not usually thought of as needing child-proofing, such as handbags and coat pockets.

Prevention is the best medicine, but when that doesn't work you need to know how to act quickly when treatment is needed. Put the phone number for the National Capital Poison Control Center (625-3333, 24 hours a day) in a handy place. I recommend a sticker on your telephone. The center's staff is well trained in handling most emergencies by phone and telling you when more help is needed.

Every household with children should have a bottle of ipecac syrup, which induces vomiting and can be bought without a prescription. But you should use ipecac only after checking with your physician or poison control center.