Asthma rates in children may finally be abating . . . somewhat
Asthma is by far the most common chronic lung problem in children, affecting nearly 10% of all children. It may even be the most common chronic health problem of any sort if you exclude obesity. What is it?
Here is a schematic drawing of what a normal lung looks like:
You can think of the lungs as being composed of two parts. The first is a system of conducting tubes that begin at the nose and mouth, move through the trachea (windpipe), split into ever smaller tubes, called bronchi, and end with tiny tubes called bronchioles. The job of this system is to get the air to the business portion of the lungs, which are the alveolar sacs. This second part of the lung brings the air right next to tiny blood vessels, or lung capillaries. Entering capillary blood is depleted in oxygen and loaded with carbon dioxide, one of the waste products of the body’s metabolism. What happens next is gas exchange: as the blood moves through the capillaries, oxygen from the air we breathe in goes into the blood, and carbon dioxide leaves the blood and goes into the air we breathe out. The newly recharged blood then leaves the lungs in an ever enlarging system of pulmonary veins and then goes out to the body.
The main problem in asthma is that the conducting airway system gets blocked in several ways, so the oxygen can’t get in and the carbon dioxide can’t leave. Although both are a problem in a severe asthma attack, getting the air out is usually a bigger issue than getting it in because it is easier for us to generate more force sucking in air than blowing it out. So the hallmark of asthma is not getting the air out — called air trapping. Why does this happen? There are two principal reasons: for one, the small airways, the bronchioles, constrict, get smaller; for another, the walls of the airways swell and the airways themselves fill with excess mucous, blocking air flow. Here’s another schematic drawing of what that looks like.
Thus during an asthma attack these things happen, all of which act together to narrow the airways and reduce air flow:
- The smooth muscle bands around the tiny airways tighten
- The linings of the airways get inflamed and swell
- The mucous glands in the airways release too much mucous, filling the airways
The medicines that we use to treat asthma work by reducing (or even preventing) one or more of these things.
Between 1980 and 1995 the prevalence of asthma in children doubled. Then from 1995 to 2010 the number continued to increase, but more slowly. Where are we now? A recent report in Pediatrics, the journal of the American Academy of Pediatrics, gives some answers. The authors looked at the time period from 2000-2013. They separated patients by gender, race, geographical location, and socioeconomic group.
The investigators found that across all groups asthma prevalence steadily increased from 2000-2009, although the rate of rise had slackened compared with the previous 2 decades. The year 2009 was the peak. After that there was a plateau, and since then the rates have actually fallen a bit for the total group. Among poor children, however, asthma rates have continued to rise steadily. This is concerning. The reasons for these changes in asthma prevalence are complex and experts think it is most likely an interplay of several things. If you are interested you can find more information in the article linked above. But it does appear that, on balance, the “asthma epidemic” is abating.