Dear Doctor: My doctor diagnosed me with food-allergy-related angioedema and sent me to an allergist, who couldn't find a cause. I'm afraid to eat anything because I never know when it's going to flare up, making my tongue, lips and inner mouth around my gums swell. I take Zyrtec and Benadryl, but they're not especially helpful. What else can I do?

Dear Reader: Angioedema can be very frustrating, especially when not controlled. For those unfamiliar with the condition, angioedema is an extreme swelling of the skin and sometimes other tissues. It occurs when fluid leaks from small blood vessels into the surrounding tissues, a process triggered by the release of inflammatory chemicals within the body. The swelling can be dramatic, especially when it occurs in the face and lips -- even life-threatening when it affects the throat or bronchi, or when a dilation of blood vessels leads to a severe drop in blood pressure. Angioedema is sometimes associated with hives.

As you can attest, identifying a cause can be difficult. In 38-41 percent of people with angioedema, no cause can be found. In only 16 percent of people is a specific trigger identified. This can be a food, environmental allergen, insect bite or drug (besides ACE inhibitors). As for ACE inhibitors, these anti-hypertensive drugs are responsible for 11 percent of cases; the related angiotensin receptor blockers (ARBs) can also -- on rare occasions -- lead to angioedema. So, too, can aspirin and other NSAIDs, such as ibuprofen and naproxen.

Genetics can play a role as well, with deficiencies in a protein known as C1-esterase inhibitor leading to uncontrolled inflammation in the body, including episodes of angioedema. Although these deficiencies are hereditary, they also can be acquired though bone marrow or autoimmune disorders. The hereditary form is exacerbated by trauma, infection, emotional stress and dental procedures, as well as estrogen exposure via pregnancy, oral contraceptives or hormone replacement therapy.

It appears that your doctors have narrowed the cause to a food allergy, but you should still be cautious about other risk factors. I would avoid aspirin or other NSAIDs, as well as ACE-inhibitors or angiotensin receptor blockers. You should also be assessed for a potential deficiency in C1-esterase inhibitor. If deficiencies are found, treatments can either replace the inhibitor or decrease the inflammation.

Although they haven't worked especially well for you, allergy medications Zyrtec and Benadryl can often be helpful in controlling the bouts of swelling. Note that higher doses of Zyrtec (cetirizine) at 10 milligrams twice a day have been shown to be more helpful than lower doses. Some doctors have found success with very high doses -- up to 20 milligrams twice a day -- but the impact of such use has not been officially studied.

When outbreaks do occur, they can be quickly stopped with the use of the steroid prednisone at 40 milligrams daily in addition to Benadryl. Case reports suggest immune-modulating medications such as Rituxan and Firazyr may be beneficial, but their use needs to be studied more.

While angioedema is not an easy condition to live with, I hope a higher dose of antihistamines and an avoidance of exacerbating factors will give you greater control over the condition.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: How did oxygen therapy help the brain of that toddler who almost drowned a few years ago? Has the child completely recovered from her near-death experience?

Dear Reader: The incident you're referring to happened in Arkansas in 2016, when a toddler who had just learned to walk managed to slip through a latched baby gate in her home. The little girl, who was 23 months old at the time, then entered her backyard, where she fell into the family's swimming pool. Although it isn't known exactly how long the child was in the water, news reports say it was at least five minutes and perhaps as long as 15 minutes. When her family found her, she wasn't breathing.

Despite nonstop CPR administered first by her mother and then by paramedics, it would be more than 1 1/2 hours before the child's heart began to beat on its own. At the hospital, MRI scans revealed extensive brain damage. When she returned home five weeks later, her profound brain injury was clearly apparent. The child had no motor control. She was unable to sit up or speak and had to take all nourishment through a feeding tube. Due to the brain injury, the toddler's body sometimes would "forget" to breathe while she was asleep. Alerted by a monitor, her parents would rush to resuscitate her.

Research into brain injuries and their treatment led the family to an expert in hyperbaric medicine at LSU Health New Orleans School of Medicine. Hyperbaric oxygen therapy is perhaps best known as the treatment used for decompression sickness, a complication that occurs when scuba divers resurface too quickly. It is also used to treat serious infections and wounds that won't heal. (Although some non-medical practitioners make claims that it can treat conditions like Alzheimer's disease, depression and spinal cord injury, there is no evidence of that at this time.)

In this type of therapy, the patient is provided with a higher percentage of oxygen than is available in the air we breathe. Most commonly, this involves a pressure-controlled chamber filled with pure oxygen. When the pressure of the chamber is raised -- it can be up to three times normal air pressure -- the lungs are able to deliver significantly increased amounts of oxygen to the tissues of the body.

In this case, oxygen delivered first via a tank and a mask, followed by several months of treatment in the hyperbaric chamber at the New Orleans clinic, had remarkable results on the child. She went from being profoundly injured to what her parents now say is a normal 3-year-old. Brain scans taken five months after the near-drowning reveal only mild injury to the brain. The shrinkage that accompanies serious brain injuries was also reversed.

It's not known exactly how hyperbaric oxygen therapy heals tissues at the cellular level. In this particular case, there is some speculation by researchers that the child's age, at which tissues are already rapidly growing, played a role in her recovery. The toddler's experience is unique enough that a case study was published last year in the journal Medical Gas Research.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: I've suffered from atrial fibrillation for several years now. I recently read that overall heart health could reduce the risk of the condition. Is it too late for me, considering I've already been diagnosed?

Dear Reader: You're not alone in asking this question, especially in light of this new report. Atrial fibrillation, or AFib, affects more than 2 million people in the United States, making it the most common heart-rhythm abnormality in the country.

For those not familiar with the condition: The atria are the chambers of the heart that pump blood into the ventricles, which are the more muscular chambers that then push blood out to the rest of the body. Injuries to the atria can happen for a variety of reasons, leading to abnormal electrical conduction and what is known as atrial fibrillation. In these circumstances, the atria quiver instead of contracting rhythmically, creating the possibility that the blood in the chambers will form a clot, travel to the brain and cause a stroke. In fact, 15 percent of all strokes are caused by AFib.

The new study you reference assessed ways to prevent AFib. Researchers analyzed data from 13,182 men and women, ages 45 to 64, who had filled out questionnaires from 1987 through 1989 about their health habits. The participants were reassessed four more times: from 1990 through 1992; from 1993 through 1995; from 1996 through 1998; and from 2011 through 2013. Data included height and weight, smoking status, blood pressure, cholesterol levels and blood sugar levels. Questionnaires also assessed participants' diet and level of physical activity.

From all of this information, the authors divided people into three different health categories: inadequate, average or optimal. Over the years of the study, up until Dec. 31, 2014, the authors also identified those in each category who developed atrial fibrillation.

After adjusting for confounding factors, the authors found that people in the average health category had a 37 percent decreased risk of AFib compared to those in the inadequate health category. And those in the optimal health category had a 57 percent decrease in risk compared to those with inadequate health.

Note that diet and cholesterol level did not appear to have any effect upon atrial fibrillation.

One problem with the study, however is that the authors didn't explain how they adjusted for binge drinking, which is a major risk factor for this condition. In fact, AFib occurs in 60 percent of binge drinkers. But even moderate amounts can cause the abnormal rhythm. A 2014 study found that, compared to people who had less than one drink per week, those who had seven to 14 drinks per week had a 14 percent greater risk of atrial fibrillation; those with 15 to 21 drinks per week had a 39 percent greater risk of AFib. Another factor on which the researchers were unclear is how they controlled for the impact of exercise; moderate exercise decreases the risk of AFib, while extreme exercise increases the risk.

If you have had atrial fibrillation for many years, it may be difficult for your heart to resume a normal rhythm.

However, removing risk factors such as hypertension, diabetes, smoking, sleep apnea and excessive alcohol consumption can reduce the frequency of AFib. Further, among people who underwent a heart ablation procedure to stop AFib, 62 percent of those who made lifestyle changes were able to eliminate the condition, compared to 26 percent of those who didn't make such changes. And, as we said, moderate exercise may slightly decrease the risk of AFib.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)