Ask the Doctors: Carbon monoxide from cigarettes causes oxygen debt

Hello, dear readers, and welcome to a bonus letters column. Our mailboxes are filling up fast, so we'll get right down to your questions. — We recently wrote about congestive heart failure, which is when the heart becomes unable to pump enough blood to meet the body's needs. In discussing the role of smoking in developing the condition, we described how nicotine harms the body. A reader — and fellow physician — said we omitted an equally important factor: "You did not mention carbon monoxide, which is even more harmful to the heart," he wrote. "You cannot separate one from the other." Carbon monoxide, or CO, is a poisonous gas formed during the incomplete combustion of tobacco. Due to its chemical structure, CO binds to hemoglobin 200 to 300 times more readily than oxygen. That means with every inhale, a smoker sharply reduces the supply of oxygen being sent to the heart, lungs and other tissues and organs, and with each additional cigarette, keeps the body in a damaging state of oxygen debt. Thank you to our reader for this chance to revisit an important topic.

— In writing about treatment options for cluster headaches, we mentioned oxygen therapy. Cluster headaches are a severe form of headache that occur in groups, or clusters. A reader living with this condition asked for additional information. "How might I find medical-grade oxygen canisters for home treatment of cluster headaches?" he asked. "My search thus far has been unsuccessful." Medical-grade oxygen requires a prescription. Oxygen is a highly flammable gas that is delivered under pressure. Improper use can lead to an accident or to lung damage. With a prescription from the doctor who diagnosed your cluster headaches, you can receive the appropriate equipment, along with training, from a medical supplier. The prescription will also make it possible to seek treatment at a medical facility.

— In a column about grip strength, which is the force generated by the muscles of the hand and forearm, we discussed its importance as a biomarker in older age. A decline in grip strength can indicate an onset of serious health conditions, including arthritis, osteoporosis, heart disease and cognitive issues. This prompted a question from a younger reader. "I'm 37 years old, healthy and a marathon runner, but in the past few weeks, I've had a harder time holding heavy weights for long periods of time," she wrote. "I do have a history of MS in my family, but I have no other symptoms or issues. Should I be worried?" A decrease in grip strength in weightlifting can have a range of causes, including overuse, inflammation, carpal tunnel syndrome and even small changes to technique. If the weakness persists, the history of multiple sclerosis in your family makes it a good idea to check in with your doctor. MS is not an inherited disease. However, a genetic component does put family members at higher risk. Your doctor can evaluate your situation and help monitor any future changes.

Thank you, as always, for taking the time to write. We love hearing from you and will return soon with our regular monthly letters column.

Dear Doctors:

I am 14 years old and recently had to test for tuberculosis. What is the common age range for tuberculosis? I did some research and learned that there are both latent and active tuberculosis infections. What is the cause of this dormant phase in tuberculosis bacteria?

Tuberculosis is a serious infectious disease caused by bacteria that can affect anyone at any age. Although it usually infects the lungs, the bacteria can travel via the blood to other parts of the body. This includes the spine, lymph nodes, kidneys and brain.

Here in the United States, most cases of tuberculosis, or TB, are caused by Mycobacterium tuberculosis. It spreads through the air on minute droplets that someone with an active lung infection emits when they sneeze, cough, shout or sing. To become infected, you must be close enough to inhale the bacteria-laden droplets.

Not everyone infected with TB bacteria gets sick. As you point out, this is known as a latent infection. It means that although the bacterium is present in the body, it is not actively growing or reproducing, and, thus, not causing symptoms. That's because the

Dear Reader:

immune system has identified the bacteria as a threat and successfully isolated it. It is estimated that as few as 10% of people infected with TB bacteria go on to develop the active form of tuberculosis. However — and this is why testing is important — it is possible for the bacteria to become active at any time. The shift can occur when additional burdens on the immune system — such as illness, extreme stress or immunosuppressive treatment for another condition — allow the bacteria to grow and multiply.

Active disease can occur anywhere from a few weeks to many years after an initial infection. Infants, young children, older adults and people living with weakened or suppressed immune function are at highest risk. Symptoms include a persistent cough not associated with a viral infection, weakness, fatigue, chest pain, shortness of breath, loss of appetite, chills, night sweats, unintended weight loss, fever and bloody sputum.

Diagnosis for TB begins with a skin-prick test. If those results are positive, blood tests and chest X-rays are used to confirm the diagnosis and to determine if the infection is active or latent.

Both latent and active forms of TB are treated with antibiotics. For latent infections, treatment can last from three to six months. Active infection requires a longer course of treatment, often with two drugs. Unfortunately, some forms of the TB bacteria have become drug-resistant, even to combinations of drugs. This has led to the development of tests to identify genetic mutations in TB bacteria. Those results are used to choose drug combinations with the best chance of outwitting the mutated bacteria.

Active tuberculosis is a potentially fatal disease. It can cause permanent damage to the lungs, and can also spread to other parts of the body, causing serious health complications, including organ damage. Tuberculosis causes millions of deaths worldwide each year. That makes it very important for anyone with a TB diagnosis to follow through with treatment.

Eve Glazier, M.D., MBA, is an internist and associate professor of medicine at UCLA Health. Elizabeth Ko, M.D., is an internist and assistant professor of medicine at UCLA Health.