DEAR DR. DONOHUE: Lately whenever I take a walk, I get such pain in my calves that I have to stop until it goes away. Is this a muscle problem or arthritis? – M.S.

ANSWER: Most likely it is a circulation problem – peripheral vascular disease. “Peripheral” indicates that arteries in the body’s periphery – arms and legs – are partially blocked by a buildup of plaque. Plaque is a mound of cholesterol, fat and blood proteins clinging to the artery wall. It’s a problem that comes with growing old. About one in six people older than 55 suffers from it.

Calf pain while walking is a hallmark symptom. The calf muscles require more blood, but the plaque on artery walls obstructs the needed extra blood flow to the muscles. Muscles, lacking the oxygen and fuel brought by blood, cry out in pain. Pain can also be felt in the thighs or buttocks if arteries to those muscles are filled with plaque.

A person can tell, almost to the inch, the distance at which pain will develop. Resting relieves the pain, and the walking can continue until the next onset of pain.

A doctor can confirm the diagnosis by taking the blood pressure in the arms and comparing it with the blood pressure in the ankle region. The two should be similar. In peripheral vascular disease, the ankle pressure will be lower than the arm pressure.

Don’t take a nonchalant attitude about this. Peripheral vascular disease is often a tip-off that arteries supplying the heart and brain are also partially blocked, and blockages there are a prelude to a heart attack or stroke.

Treatment for obstructed arteries entails lowering blood cholesterol to stop plaque enlargement. A supervised exercise program is most important. Medicines such as aspirin, Pletal and Plavix can enhance blood flow through involved arteries. Opening the arteries by squashing the plaque with an inflated balloon or bypassing the obstructed segment with a graft also works – two procedures borrowed from treatment of blocked heart arteries.

The peripheral vascular disease pamphlet answers the unanswered questions you most likely have about this common disease. To order a copy, write: Dr. Donohue – No. 109, Box 536475, Orlando, FL 32853-6475. Enclose a check or money order (no cash) for $4.50 U.S./$6.50 Can. along with the recipient’s printed name and address. Please allow four weeks for delivery.

DEAR DR. DONOHUE: My father, 82, lives with us and is in good mental and physical health. He complains that he cannot get to sleep at night because he hears his heart beating loudly in his ears. What can he do? – S.G.

ANSWER: Often the sound of the heart beating in an ear comes from arteries adjacent to the ear that have become hardened and amplify the sound of the heartbeat. If your dad sleeps on his back, have him try sleeping on his right or left side. A change of position can sometimes eliminate the sound. Propping up the head with pillows might also get rid of the noise.

Some serious conditions can be at work. High blood pressure, obstructed neck arteries, Paget’s disease (a bone disease), anemia and tumors near the ear are examples. Your father ought to mention the problem to his doctor so a few simple tests can reveal whether one of these serious problems is producing his symptom.

DEAR DR. DONOHUE: I am doing a project on twins, and I wonder if you would be kind enough to furnish me with some information. What’s the difference between identical and nonidentical twins? How often do twin births happen? Does it run in families? – T.J.

ANSWER: Identical twins come from one fertilized ovum that splits in two. Identical twins have the same genes. Nonidentical twins, on the other hand, come from two different ova that have been fertilized simultaneously. They do not share the exact same genes. These twins are called fraternal or dizygotic.

Twin births happen in 1 percent to 2 percent of all births.

Family history does figure into twinning. When there is a history of twins on the mother’s side of the family, then the chances for twinning increase.

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.