Dear Doctor: I've had lower back pain for years, but I can't afford to go to a physical therapist. My husband, who started taking a yoga class at the community center here a few months ago, swears that his back pain is going away. Just how effective is yoga for lower back pain?

Dear Reader: When it comes to back pain, you and your husband have plenty of company. It's estimated that 80 percent of all adults will experience it over the course of their lifetimes. And little wonder.

The spine is a feat of engineering. Bones, joints, muscles, ligaments, nerves and other specialized tissues interconnect to form a strong and flexible column. They bear the weight of the upper body while providing an axis from which we can stretch, bend, reach and pivot. But when any one part of the spine moves out of alignment, whether due to injury, illness or overuse, the result is pain and, occasionally, immobility.

Your question addresses pain in the lower back, which is also known as the lumbar spine. And for that, we have some promising news. The results of a recent study by researchers at the Boston Medical Center suggest that practicing certain yoga poses is a viable alternative to physical therapy for dealing with chronic lumbar pain.

The study recruited 320 adults who were living with chronic lower back pain that they rated from moderate to severe. The participants were divided into three separate treatment groups.

One group took part in 15 one-hour physical therapy sessions over the course of three months, and was assigned additional exercises to do at home. A second group took weekly 90-minute yoga classes over the course of the three months, and was also assigned additional home exercises. The third group of participants did not take part in any kind of treatment. Instead, they received a self-help book about back pain, occasional newsletters with information about lumbar health and access to telephone check-in sessions.

After the first three months of the study, the yoga group and the physical therapy group each continued with their forms of therapy for an additional nine months. When the study concluded a year after it had begun, the group that underwent physical therapy and the group that took yoga classes self-reported similar improvement in both pain levels and improved mobility.

Both of these groups reported feeling better than the group that was given only back pain literature. In addition, the individuals in the physical therapy group and the yoga group were more likely to have stopped using medication to manage their pain.

But before you rush out and sign up for any old yoga class, it's important to note that the exercises done by the participants in this study were geared specifically to address issues of the lumbar spine. That means that the areas of the spine targeted by the yoga postures, as well as the pace of the exercises and their intensity, were carefully calibrated.

If you decide to give yoga a try, find an experienced teacher and be sure to let her or him know your specific limitations.

(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: A few months ago, I started to hear pulsating sounds in my head. I finally came to realize it was my blood pulsing. The sound is always there, but really only noticeable when I'm in bed or sitting quietly. Is it anything to worry about? Will it ever go away?

Dear Reader: What you're describing sounds like the symptoms of pulsatile tinnitus. Tinnitus is normally perceived as a ringing, buzzing or whistling sound in the ear. Pulsatile tinnitus, however, is a pulsing sound synchronous to the heartbeat. It occurs in less than 10 percent of people who have tinnitus. I have had patients, and a family member, with pulsatile tinnitus, so I understand how intrusive and irritating the sounds can be, especially when one lies down at night. Usually, this type of tinnitus is heard in just one ear.

The biggest issue with pulsatile tinnitus is finding the source. Often the pulsing sensation is caused by malformations between the arterial system and the venous system and the ensuing turbulent blood flow that occurs when blood moves from a high-pressure system, the artery, to a low-pressure system, the vein.

Pulsatile tinnitus can also occur when the temporal bone transmits the sound of a nearby artery -- or from more serious conditions, such as when a nearby artery suffers an aneurysm, when a carotid artery narrows, or when a person develops a paraganglioma (a tumor that can occur in the neck and in the head). Often, these tumors are located near blood vessels and have a good blood supply, leading to turbulent blood flow that is audible not only to the person but also sometimes the doctor. Elevated blood pressure in the brain and anemia can play a role in pulsatile tinnitus as well.

Due to concerns about aneurysms, malformations, narrowing of the carotid artery and paragangliomas, it is important to try to identify the cause of the pulsatile tinnitus. Diagnostic testing can detect an underlying cause in 70 percent of patients. To get to a diagnosis, your doctor will need to take a thorough history and do a focused examination.

Radiologic tests then may be necessary to find the cause. An MRI of the brain with MR angiography can identify vascular abnormalities and brain tumors. A CT scan with angiography can also identify vascular lesions and tumors, but not as well as an MRI. One differentiating benefit with a CT scan is that it can identify bony lesions near the ear that would lead to pulsatile tinnitus.

So, I wouldn't ignore the sounds you're hearing. You should make an appointment with your primary care doctor or an ear, nose and throat doctor to evaluate the cause of your symptoms. They may recommend imaging to try to identify the cause, as well as treatment for some of the conditions related to pulsatile tinnitus. Then, finally, you may find relief from this irritating symptom.

(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: What's the deal with the tick bite that makes you allergic to meat? Will I know if it happens to me?

Dear Reader: Sounds like science fiction, right? A single tick bite scrambles your immune system so that overnight you become allergic to foods you've been eating your entire life. But unfortunately for a small but growing number of people in the United States, this scenario is all too real.

The culprit is the Lone Star tick, which is widely distributed throughout the Eastern, Midwestern and Southeastern states. Recent studies suggest that the tick may be on the move. It has been identified as far north as New York state and Maine, and as far west as Texas. It gets its name from the single splotch, or "star," that the adult female has on her back.

It was in 2009 that scientists first began to connect the dots between the Lone Star tick and a rather unusual immune response. Certain people who were bitten by the tick went on to develop a sudden and sometimes quite serious allergy to red meat. This includes beef, lamb and pork.

Something in the tick bite sends alarm bells ringing in the immune system, ordering it to target a specific carbohydrate found in meat. The full name is galactose-alpha-1,3-galactose, but it's commonly shortened to alpha-gal.

The specific agent that causes the allergy, be it a microbe or a biological compound found in the tick's saliva, is under study. So far scientists have been left with far more questions than answers. This includes whether the sensitivity to alpha-gal can be reversed.

In most food allergies, the physical response is swift. Eat a strawberry and a few minutes later, you break out in hives. With the alpha-gal allergy, however, it can take the body up to 12 hours to react. The slow onset of alpha-gal allergy symptoms can make the diagnosis a challenge.

The most common symptoms are stomach pain, nausea, hives, skin rash, sneezing, headaches and wheezing. In severe cases, anaphylactic shock is possible. The allergic reaction can happen after just a single bite of meat. It has also been observed in people taking medications that contain gelatin, as well as those using new cancer drugs derived from genetically modified mice.

The recent spread of the alpha-gal allergy beyond the traditional borders of the Lone Star tick's range has scientists questioning whether other species of ticks may also be involved. If you've recently been bitten by any tick and suspect you may have developed an alpha-gal allergy:

-- Stop eating red meat or any other foods that trigger symptoms.

-- Know that some symptoms can be controlled with antihistamines and corticosteroids.

-- For severe reactions, including anaphylaxis, use injected epinephrine, which requires a prescription.

For an accurate diagnosis, make an appointment with an allergist. He or she will want to know:

-- What you ate that triggered the symptoms.

-- The time frame in which symptoms appeared.

-- The specifics of the symptoms and how long they lasted.

A blood or skin test will show whether food-specific antibodies are present. Your allergist will use the results of these tests to arrive at a diagnosis.

(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.)