Friday, March 26, 2010

History of Exercise Induced Bronchospasm

If you have asthma chances are you have exercise induced asthma (EIA), statistics show about 80% of asthmatics have it. Yet prior to 1966 few understood EIA.

I happened upon a book called "Allergy: Principles and Practice Volume II (5th edition, Elliot Middleton, editor, 1998) which, on page 953, so happened to have a good review of the history of EIA, which has actually since been changed to EIB (exercise induced bronchospasm). To learn more about EIB you can check out this link.

In upcoming posts on this blog you will get to know the asthma experts such as Sir Joh Floyer and Fredrick Hyde Salter that are mentioned below, for now all you need to know is they were physicians who helped shape the history of the disease you and I have: asthma.

E.R. McFadden, Jr, wrote the following history of EIA:

"EIA was formally brought to the attention of clinicians of the modern era in 1966. Actually, the association between strenuous exertion and the acute development of airway obstruction was originally recorded by Arateaus the Cappadocian in the first century AD.

It was then rediscovered in 1968 by Sir John Foyer, who was the first to point out the relationship between the level of ventilation and the severity of symptoms. In 1864, Salter (Fredrick Hyde Salter) recognized that the postexertional obstructive response could be accentuated if the exercise was performed in a cold environment. He too suspected the importance of the absolute level of ventilation achieved during exertion and suggested that the rapid passage of fresh and cold air over the bronchial mucous membrane could stimulate the airways either in a direct manner or by production of nervous system irritability (he believed asthma was a nervous disease). The importance of these thoughts were unrecognized until recently.

It wasn't until 80 years later, McFadden writes, that a man named Herxheimer published works on his theories about what EIA was. He actually believed that "hyperventilation during exercise was the key factor, but he reasoned that it brought about its effects through the constrictor action of airway hypocapnea (low CO2)."

When you breath fast you blow off CO2, and was believed to (through a series of reactions) to cause bronchospasm (airway narrowing). This was later disproven.

While others agreed with Herxheimer, some believed substances released from the muscles during exercise (such as lactic acid) were the stimuli that caused EIA.
This theory, as well as the theory that low CO2 caused EIA, were found to be false in 1977.

What was not considered back then was temperature and humidity of the air inspired were important factors in the cause of EIA.

While scientists are still digging for all the facts about EIA, it appears we're pretty close. On a recent post at MyAsthmaCentral.com, I reported on the up to date definition of EIA. So here I quote myself:

"The best definition I could find came from this post at AAAAI.org, which notes exercise doesn't necessarily "cause" asthma, but that "hyperventilation (fast breathing) associated with exercise cools and dries the upper and lower airway resulting in the release of histamine and other substances that produce the bronchospasm (spasming of the muscles in the air passages in your lungs)."

Likewise, when an asthmatic exercises when the temperature is cold, and the air dry, "Hyperventilation of cold dry air produces a similar response."

In this way, asthmatics are more likely to have asthma symptoms when they exercise in cold, dry air.

Dr. Randolph also said it isn't so much the cold weather that triggers the asthma attack, but the fact that the air is dry. Asthmatic lungs have a diminished ability to humidify the air, and this triggers the asthma response. This has been proven via various studies.

AAAAI.org also notes it doesn't help that "During strenuous activity, people tend to breathe through their mouths, allowing the cold, dry air to reach the lower airways without passing through the warming, humidifying effect of the nose."

Actually, according to Dr. Christopher Randolph, a clinical professor at Yale University who was interviewed by The New York Time's, EIA is not quite the same as asthma. He notes the "'preferred term' in the scientific community for exercise-induced asthma is exercise-induced bronchoconstriction, or EIB."

So by default we'll probably continue to call it EIA, although it's actually EIB. And that's why I titled this post, "History of EIB."

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