DEAR DR. DONOHUE: Both my wife’s legs are swollen from her knees to her feet. She can barely walk on them.

Her doctor told her there is not much he can do. He told her that the condition is lymphedema. What can we do for her? – M.I.

ANSWER: Lymph is fluid that bathes and nourishes all cells and tissues. “Edema” means swelling. Lymphedema, therefore, is swelling due to too much lymph fluid.

One common cause is a disruption of lymphatic vessels – open-ended hoses, very similar to blood vessels, that suction up lymph fluid and return it to the circulation.

Another cause is scarred and damaged lymph nodes. They are sanitation depots that cleanse lymph of foreign matter on its way back into the circulation.

A third cause is surgery. After many surgical procedures, lymph vessels and lymph nodes are either removed or traumatized.

A common consequence of breast surgery is a swollen arm due to a disturbance of lymph vessels and lymph nodes. If your wife keeps her legs elevated as much as possible, especially when she sits, that drains some fluid out of her legs.

Most important is for you to locate a therapist experienced in massaging limbs swollen from lymphedema.

The National Lymphedema Network can help you. The number is 800-541-3259. The network’s Web site is: www.lymphnet.org.

Special pneumatic pumps also drive fluid out of lymphedema-swollen legs.

Your wife has lymphedema and not edema, correct? Edema is fluid accumulation in a limb, usually the legs, due to heart failure, kidney disease or liver problems.

Edema and lymphedema look very much alike, but the treatment for edema is quite different from the treatment for lymphedema.

The booklet on edema and lymphedema covers these two topics in detail. Readers can obtain a copy by writing: Dr. Donohue – No. 106, Box 536475, Orlando, FL 32853-6475. Enclose a check or money order (no cash) for $4.75 U.S./$6.75 Can. with the recipient’s printed name and address. Please allow four weeks for delivery.

DEAR DR. DONOHUE: Is there such a thing as stomach flu? – L.D.

ANSWER: There is a thing that many people call “stomach flu,” but it’s not the flu and it’s not caused by the influenza virus. True flu is a respiratory illness. People cough, have a fever and their muscles hurt.

They take to their beds because they feel so awful. They don’t have stomach cramps or diarrhea. The flu is due to the influenza virus, and this is the illness that the flu shot wards off.

Stomach flu is something that covers a wide variety of symptoms, like stomach cramps, diarrhea and sometimes vomiting.

A large number of viruses are responsible for it, but the influenza virus is not one of them. The flu shot doesn’t prevent this illness.

It would a boon to humankind to get rid of the diagnosis of “stomach flu.” It’s a source of confusion to many people.

DEAR DR. DONOHUE: I am a 69-year-old male in good health except for a slight increase in blood pressure.

Following a knee replacement a year ago, I have resumed my exercise program of walking two miles a day in 24 minutes.

I’m 6 feet tall and weigh 195 pounds. I now prefer to ride my bike the same two miles on flat roads at a speed of 14 miles an hour.

Obviously, this takes less time. I am breathing heavily and have a nice sweat when done. I prefer the quick bike ride to the half-hour walk.

Am I getting the same benefits from the bike exercise as from the walk? My family doctor says it’s the distance that counts. I feel it should include effort – namely, speed. What do you say? – P.M.

ANSWER: Intensity (how hard the exercise is; your “speed”) and duration (the amount of time spent exercising) are two important ingredients of exercise. Neither can make up for a deficit in the other.

Your walk of two miles in 24 minutes puts your pace at 5 miles an hour. That’s pretty fast. It’s not walking. It’s jogging.

At that clip, you are burning more than 10 calories a minute. Twenty-four minutes is close to 30 minutes a day, the time duration recommended for keeping the heart healthy.

Biking is equally as good an exercise as walking is. Pedaling at a pace of 14 miles an hour burns just about the same number of calories that jogging at 5 miles an hour burns.

However, the time you spend biking is only 9 minutes. The intensity is fine; the duration leaves something to be desired. You have to do three biking sessions a day to get the recommended exercise time in.

The biking doesn’t have to be done in one long session. It can be three sessions of the same time that you now spend.

Dr. Donohue regrets that he is unable to answer individual letters, but he will incorporate them in his column whenever possible. Readers may write him or request an order form of available health newsletters at P.O. Box 536475, Orlando, FL 32853-6475. Readers may also order health newsletters from www.rbmamall.com