DEAR DR. DONOHUE: Recently in the news was the case of a woman who suffered brain damage due to a chemical imbalance. It mentioned a potassium imbalance. What does “chemical imbalance” mean? And what is a persistent vegetative state? – G.R.

ANSWER: With the arrival of the knowledge that the basis of many psychological problems, like depression, lies in an imbalance of brain chemicals, “chemical imbalance” has come to mean that brain chemistry has gone awry.

Long before that meaning of the term came to the fore, a “chemical imbalance” referred to a disturbance in the levels of blood chemicals such as sodium, potassium, bicarbonate and chloride. That meaning still endures, so there are two valid definitions of “chemical imbalance.” A person has to know the context of how these words are used in order to arrive at the correct meaning of the term.

Too low or too high a blood level of potassium is a chemical imbalance in the second sense. High or low potassium levels can disturb the heartbeat and initiate serious heart-rhythm disturbances, like ventricular fibrillation. Such a heart rhythm interferes with the heart’s pumping action, and too little blood gets to the brain. The result is brain death.

Potassium disturbances are common and are usually not terribly significant. It’s severe imbalances that lead to potentially fatal heartbeat disturbances.

A persistent vegetative state is a state where people are awake but unresponsive. They are unaware of what’s going on around them. They can have sleep-wake cycles, and their eyes are opened, but they cannot meaningfully interact with other people or their environment.

DEAR DR. DONOHUE: I have been told that people can check if they have a thyroid problem by drinking water and looking in the mirror to see a ball between the chin and the collarbone. Is this right? – M.R.

ANSWER: You’re talking about a goiter – an enlarged thyroid gland.

The thyroid gland is located at the bottom of the neck. When a person drinks, the action of swallowing muscles causes the gland to rise in the neck. If the gland is large, when it rises it is quite visible. It doesn’t look like a ball. It looks like a large thyroid gland.

A goiter is only one thyroid-gland condition. Drinking water doesn’t disclose those other conditions. The thyroid booklet outlines the gland’s many problems and their treatments. Readers can obtain a copy by writing: Dr. Donohue — No. 401, 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: In my doctor’s examining room is a poster advertising four different drugs. The poster urges patients to take the literature below it and ask the doctor if these drugs would be good for them. Is this unethical? Do doctors push drugs manufactured by pharmaceutical companies in which they have stock? I feel that many people would be interested in your comments on the subject. – S.H.

ANSWER: I don’t know if this is ethical, but it is crass and distasteful. The doctor’s office should not be a place for drug advertisements.

Have you told the doctor how offensive you find it? Do so. If there’s no response, it would be appropriate for you to find another doctor.

DEAR DR. DONOHUE: My grandchild asked me: “Where does the itch go after you scratch it?” Can you answer this one? – J.S.

ANSWER: It doesn’t go anywhere. A truly bothersome itch stays right there, but scratching blocks the transmission of the itch signal to the brain so a person doesn’t feel it for a short time. There’s more to it than that, but I hope that satisfies your grandchild for the moment. I’m working on a longer reply, which I’ll have ready for him or her in about five years.

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.