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.)

Dear Doctor: Is it true that HIV can now be considered a chronic disease? Does that mean people are no longer looking for a true cure?

Dear Reader: To answer this, we first have to agree on the meaning of "chronic disease," which, believe it or not, has more than a few definitions. Rather than take a deep dive into those important but perhaps snooze-inducing distinctions, let's go with the most common understanding of the term. That is, a chronic disease is one that cannot be cured, but with ongoing medication and treatment can be managed. And thanks to the stunning success of antiretroviral therapies, infection with HIV now fits that definition of chronic disease.

As most of our readers probably know, HIV is shorthand for the human immunodeficiency virus. The virus undermines the immune system by attacking certain white blood cells that are vital to the ability to fight infection. The loss of these white blood cells leaves HIV-positive individuals vulnerable to disease, infection and complications of illness. AIDS is the stage of HIV infection at which damage to the immune system is profound, and patients are unable to fight off a host of opportunistic infections. For people with AIDS, infections that a healthy immune system would brush off become potentially deadly.

According to one school of thought, the antiretroviral drugs that are now the main treatment regimen for people living with HIV amount to a functional cure. But just because infection with HIV is no longer a near-certain path to developing AIDS, that doesn't mean living with the virus is problem-free. The drugs, which must be taken daily and for the rest of an infected person's life, are extremely powerful. Cumulative toxicity becomes a real concern. And while the antiretrovirals do prevent an HIV infection from progressing to full-blown AIDS, the individual's immune system remains affected by the presence of the virus and, consequently, is less robust. Add in the ability of HIV, like all viruses, to rapidly mutate and become resistant to existing drugs, and infection remains a serious condition.

Compared to the early days of the HIV crisis, when each new development in decoding and understanding the virus was heralded, things may now seem quiet on the news front. But as researchers focus on both prevention and a cure, the science continues to move forward.

For many, the idea of a vaccine is the gold standard. In that regard, there has been encouraging news from researchers at the University of Massachusetts, who recently reported that they are about to enter into a phase 1 trial to assess the safety of a potential HIV vaccine. Other scientists are looking into topical medications that can stop the virus at the site of infection.

And thanks to ongoing advances in the field of immunotherapy, there is renewed hope of finding a cure. Earlier this year, researchers at the University of Maryland reported success in engineering immunotherapeutics that target and neutralize the virus on multiple fronts and across multiple strains. (And yes, that's a greatly simplified explanation.)

An estimated 36 million people worldwide now live with HIV, and while scientific advances don't always make headlines, they do make a difference.

(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.)