QUESTION: I know shock waves are used to dissolve kidney stones. Why not use them on gallstones, which are the same thing? I'm especially interested in this subject because I have gallstones and am facing regular surgery. Is anything being done along these lines? - Mrs. B.P.

ANSWER: Yes, shockwaves for crushing gallstones are being investigated, but it's presently on hold. The name of the procedure is lithotripsy, and it is being used for kidney stones.Although the gallbladder and kidney stone situations are similar, there are some drawbacks to use of lithotripsy for gallstones. For one, the gallbladder duct, unlike the kidney's, is quite small, and often small stone fragments from the crushing can lodge there afterward. That can cause more trouble than if the stones were left intact in the gall bladder. Secondly, no one is certain that removal of the gallstones will prevent reformation later.

For the present, I don't advise your waiting around for lithotripsy as an ultimate answer. If you are told you need surgical removal of your gallbladder it would probably be best to get that done now before you have a full-scale gallstone attack.

QUESTION: I am taking the new cholesterol-lowering drug, Mevacor. I was told to take it with my evening meal. Do I really have to do that? Why can't I take it when it's most convenient? I wonder what the need for such timing is. How does Mevacor work? - W.W.

ANSWER: Mevacor (lovastatin) lowers blood cholesterol levels by stopping manufacture of it in the liver. It is a little-known fact that the liver is the source of most of our body's cholesterol.

As to the timing of lovastatin dosages, there are good reasons for the evening meal rule. The presence of food increases the amount of the drug that's absorbed. Also, more cholesterol is made at night than during the daytime. For your other cholesterol-related questions, see booklet No. 5, available by writing to Dr. Donohue/No. 5, P.O. Box 19660, Irvine, CA 92713, enclosing a long, stamped, self-addressed envelope and $2.

QUESTION: When I do sit-ups, I notice a peculiar distention in the abdominal area. I have been examined by two internists who say the condition is recti diastasis. I received too little of an explanation to satisfy me completely. Is it serious? Can I continue to do my sit-ups? Can it be corrected? - M.J.C.

ANSWER: The recti abdominis muscles are two muscles that run from the rib cage down to the pubic bone. Usually, these two bands touch one another in the middle of the abdomen, but some people are born with a small separation (diastasis) between them. This is your situation.

It is a normal variation, and needs no treatment. You can continue to do your sit-ups. You don't have to have the slightest concern unless informed otherwise by the examining doctors. You can ease your mind by expressing your concern directly to one of them.

QUESTION: I belong to Bat Conservation International. I object to your statement that bats carry rabies. It demeans their significance and is not so. - B.E.H.

ANSWER: I mean no offense to the noble bat family or to your organization. But bats do carry rabies, and rabid bats have been reported in every state except Hawaii.

C) 1989 North America Syndicate Inc.