The science of wildfire smoke: What does it do to your lungs?

You're breathing it in, that acrid air, day after day, outside and even inside your house.

The smoke from the Great Dismal Swamp National Wildlife Refuge fire is not bringing you to your knees, but it's starting to feel ubiquitous.

Where does it go? What does it do?

Dr. Jeffrey Schnader can tell you. He's a pulmonologist and a professor at Eastern Virginia Medical School who has studied the lungs.

For most healthy adults, the lungs will do just what they're designed to do - filter out impurities the smoke is spewing into the air.

But that doesn't mean you won't feel some effects, depending on several key factors:

• How close you are to the smoke;

• How heavy a dose you're breathing;

• And how susceptible you are to lung injury.

The first question to pose, Schnader said, is: What's in this purple haze?

In this case, the smoke is from wildfire, which contains a combination of gases and fine particles from burning trees, peat moss and other plants.

That can cause coughing, buildup of phlegm, wheezing, stinging eyes, scratchy throat, headaches, irritated sinuses and difficulty breathing. That's your body trying to get rid of the toxins.

Cells that line the nasal system and bronchial tubes sense the presence of an unwanted substance and signal the respiratory muscles to contract, causing you to sneeze or cough to remove the offensive intruder.

Airborne soot is small enough to be inhaled into the lungs, where it can irritate the lung tissue and damage it if the dose is heavy enough.

The cells of the respiratory system have a barrier function designed to filter out impurities in the air before it reaches tiny sacs in the lungs where oxygen is delivered to tissue and where carbon dioxide, a waste gas, is removed from the body when you exhale.

But if the system is overwhelmed with a prolonged or particularly heavy dose of smoke, or because the respiratory cells don't function that well to begin with, there can be damage to the tissue.

Sometimes that results in cells growing where they shouldn't be, or fluid leaking into places where air should be. The irritants can also cause inflammation to the muscle cells around your breathing tubes, causing them to contract and cause breathlessness.

For people with conditions like asthma, chronic obstructive pulmonary disease and emphysema, it's worse because they're predisposed to breathing problems, which may have already caused damage to their lung tissue.

Wildfire smoke also contains carbon monoxide that can enter the bloodstream through the lungs and limit oxygen going to the body's organs and tissues. People with heart disease are particularly vulnerable to carbon monoxide levels because it further reduces oxygen levels, causing chest pain and rapid heartbeat.

Older people are more vulnerable to the smoke because they're more likely to have heart or lung disease. Children are more susceptible because their breathing airways are narrow and still developing. They also tend to be outside more than adults.

Most people will be fine, but for some, damage to lung tissue can last longer than the haze.

"It may go away on its own, it may linger or it may never go away," Schnader said.

Most people think of asthma as a condition diagnosed in childhood, but it can also be acquired as an adult.

"I'll have 80-year-olds say 'I've never had asthma, why do I have it now?' " Schnader said.

Usually adult-onset asthma is due to a viral infection or an allergy. But a heavy dose of a irritating substance like smoke also can cause it.

A lot of recent pulmonary research has centered on firefighters and emergency workers of the 9/11 attacks a decade ago. Many of the first responders exposed to the heaviest dose of smoke developed what's been dubbed "World Trade Center Cough," a persistent cough and other asthma-like symptoms that lasted long past the fire. Some firefighters' respiratory illness caused them to retire.

That smoke, though, differed from wildfire smoke because it contained toxins from glass fibers, gypsum, concrete and paper.

State air quality control officials say the worst air conditions have been near the Virginia-North Carolina border, but wind shifts figure heavily into who bears the brunt of smoke.

Today winds are expected to be from the southeast, which would mean it would be traveling north and west, more toward Richmond and Petersburg.

But any wind shift could put Hampton Roads back in its path. And because the fire is still flaming and smoldering, smoke may be around for a while.

Your nose will give you the first hint, Schnader said. "If you can smell it, you're being exposed."

Elizabeth Simpson, (757) 446-2635, elizabeth.simpson@pilotonline.com