DEAR DR. DONOHUE: I have had a chronic cough for about three years. I have been treated for allergies, asthma, postnasal drip and acid reflux, and I am still coughing. Can you suggest anything? – S.B.

ANSWER: A cough clears the lungs and airways of secretions and foreign material. It’s a reflex over which a person has little control. A cough that lingers is no longer serving a useful purpose. Constant coughing irritates the respiratory tract, and the cough becomes self-perpetuating. Finding its cause and eliminating it is the only way to obtain a cure. The search requires at a minimum a chest X-ray, pulmonary-function studies (tests that evaluate how well the lungs work) and perhaps lung scans and lung scopes.

The common causes of a persistent cough are chronic bronchitis, usually due to cigarette smoking; hidden infections like TB; and the most dread of all causes – cancer. I am sure these things have been checked for you.

You’ve also been investigated for three frequent and often-overlooked causes of a constant cough. Asthma is one. There is a form of asthma, cough variant asthma, that doesn’t lead to wheezing and episodes of breathlessness. Cough is its only symptom. The trickle of thick mucus into the throat and airways produces the cough of postnasal drip. And heartburn is an underappreciated cause of a constant cough. So are some medicines, with ACE inhibitors – a class of blood-pressure drugs – leading the list.

After an exhaustive search you might be one of those people for whom a cause is never found. Then you have to fight it blindly. If you have a dry house, especially a dry bedroom, get a humidifier. Dry airways bring on coughing spells. You might be forced to take medicines that suppress coughing. Suppressing the cough soothes the airways. Medicines with dextromethorphan often work. Robitussin and Vicks 44 Cough Relief are two examples. You could also try Atrovent. It comes as an inhaler, and it has given some chronic coughers relief from their coughs.

DEAR DR. DONOHUE: What is CLA (conjugated linoleic acid)? What is l-carnitine? Are these supplements safe? Do they work? – F.K.

ANSWER: CLA is a polyunsaturated fatty acid. Polyunsaturated fats and fatty acids don’t raise blood cholesterol like the saturated kinds do. It’s found in milk, beef, lamb, poultry and eggs. CLA supplements usually come from safflower or sunflower oils.

CLA is touted as an adjunct for weight loss. It is also said to decrease blood cholesterol, lower body fat, prevent cancer, arrest artery hardening and lower blood sugar. Animal studies show some benefits. Human studies have yielded conflicting results. I am skeptical of any product that claims so many benefits. It appears to be safe. If you want to try it, there’s no reason not to.

L-carnitine is an amino acid. Amino acids are the basic units of proteins. L-carnitine is involved with fat-burning and, therefore, is promoted for weight loss. It also takes part in getting rid of waste products generated by cell chemistry. It’s been touted to lessen the chest pain of angina, improve circulation through clogged arteries, relieve congestive heart failure and improve athletic performance. Believing it can do all this is a bit hard to swallow. There is evidence that it can do some of these things to a modest degree. It too has had no reported serious side effects.

My advice is not to substitute either of these products for prescribed medicines. You can take them as an experiment if you wish to and if you can afford to. Tell your doctor if you do. Don’t look for miracles.

DEAR DR. DONOHUE: I am scheduled for cataract surgery and am confused. My operation is called extracapsular. A friend told me she had intracapsular removal. Which is better? – O.O.

ANSWER: Extracapsular cataract surgery is the more commonly performed procedure these days. In this type of surgery, the capsule is left in place, and just the cataract is removed. The capsule is the back support of the natural lens. It’s left to provide support for the artificial lens, which replaces the clouded natural one.

Intracapsular cataract surgery removes both the cataract and the capsule.

DEAR DR. DONOHUE: I belong to an HMO. I have had three doctors and am on my fourth. They come and go. Today I went to my newest doctor, and he told me I have an irregular heartbeat and said it is atrial fibrillation. He said it could cause a stroke. He also said he is going to put me on Coumadin and monitor the thinness of my blood. I would like your personal opinion on this. – B.C.

ANSWER: The atria are the heart’s upper left and right chambers and the place where the heartbeat originates. Atrial fibrillation is a degeneration of the heartbeat into a jumble of erratic signals that cause the atria to beat rapidly and feebly. The ventricles – the heart’s lower pumping chambers – also beat rapidly and irregularly, but they can still function as pumps – in a slightly diminished fashion.

The great danger of atrial fibrillation is the formation of blood clots in the quivering atria. Pieces of those clots can break loose and be swept in the circulation to brain arteries. If they block a brain artery, as they frequently do, a stroke results. Atrial fibrillation is responsible for up to 20 percent of all the strokes that occur yearly in the United States and Canada.

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.

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