Thursday, April 17, 2014

1860: Why do young people outgrow asthma?

For many centuries it was believed that most cases of asthma were present in children, and that as one ages the asthma has a high tendency of disappearing.  The first person, to my knowledge anyway, to come up with a theory as to why this was believed, was Dr. Henry Hyde Salter. 

Dr. Salter believed that asthma was a nervous disorder, and that some exciting cause excited the nervous system and this ultimately caused spasms of the bronchial muscles that constricts the air passages.  When this occurs blood in the pulmonary vessels is unable to move through the blocked portions of the lungs, and becomes congested. 

When asthma is pure (free from any organic changes), it is intermittent, meaning that the attacks come upon the patient and then go away for a long period of time prior to occurring again.  The period of time between the attacks is random or periodic and cannot be predicted. 

Salter believed asthma was more likely to be of the pure form the younger people were when they acquired it.  So asthmatics under the age of 15 had a greatest chance of outgrowing it, those between 20 and 40 a fair chance, and over 40 a rare chance. 

"Now, why is this?" Salter asked.  "Why, caeterus paribus, (everything else being equal) should age have such a determining influence on the tendency of asthma?

He answered his own question:

1.  The young are more capable of repair:  "Partly for the reasons that I have mentioned—that in the young the powers of repair are great, in those advanced in life feeble; that in the young the pulmonary congestion that always accompanies asthma completely vanishes in the intervals of the attacks, the capillaries recover their tone, and the nutritional balance of the lungs is regained; whereas in the old the engorged capillaries are slower in recovering themselves, and the pulmonary congestion hangs about the patient some time after the asthmatic spasm has disappeared, manifesting itself by a profuse mucous exudation, and a certain thickness of breathing and incapacity for exertion. If the attacks are frequent this pulmonary congestion never entirely vanishes, and thus is produced a kind of spurious chronic bronchitis, with a tendency to aggravation by each attack, which is one of the worst and commonest complications of the asthma of the old."

2.  The young are less likely to develop chronic bronchitis:  "Another complication of asthma—dilated right heart —is much more apt to occur in the old than in the young, and for the very reason that the dyspnoea in the old is so apt, by the generation of this spurious bronchitis of which I have been speaking, to pass from the occasional and intermittent form characteristic of pure asthma, and become continuous and permanent . As far as I have seen, the right side of the heart never becomes dilated by asthma, however severe the dyspnoea may be during the attacks, if the intervals between them are considerable, and the recovery in those intervals complete. It is a continued and not an occasional and transient arrest of the pulmonary circulation that dilates the right side of the heart. It is from this fact that we see dilatation of the right side of the heart, venous stasis, and general dropsy so much more common as a result of chronic bronchitis than of asthma."

3.  The young have more room for hope:  "But this greater disposition in asthma to produce organic change in the old than in the young is not the only circumstance which imparts to age its determining influence on the tendency of the disease. In asthma, as in all other constitutional disorders, we have in the young much more room for hope from those changes in the type and build of the constitution which in them are so marked and striking; whereas in the old the constitution is set and fixed, and we have but little to hope on this score. Indeed, the existence of a constitutional peculiarity in a child is of itself almost a presumption that he will one day lose it; while in an old person it furnishes a presumption equally strong that it is fixed and indelible.

4.  Young lungs have more time to recover between fits:  "Again, in an old person the probability is that the asthma has existed longer than in a young one, and, as I shall show presently, the chances of recovery from asthma (as is the case in almost all diseases) are in inverse proportion to the length of time that the disease has existed."

5.  The young are more likely to have pure nervous asthma:  "But there is a special reason, depending on the nervous nature of asthma, that makes us sanguine of recovery in the case of the young, and which explains at the same time the greater frequency of pure nervous examples of the disease in the young than in the old. What, for want of a better name, we must call "nervous irritability" is much more marked in the young than in the old. It appears continuously to diminish from birth forward. Sources of irritation that in the young are adequate to the production of the most violent nervous phenomena, in mature life are powerless to produce such effects. The cutting of a tooth, for example, will send an infant into epileptic convulsions: one never hears of a fit from the second dentition. A young child will grind its teeth, or even be violently convulsed, from the presence of ascarides in its rectum; but one never sees such results from worms in the adult. And thus the diminution of nervous irritability, as childhood passes into youth and manhood, may make an attack of asthma less and less prone to occur on the supervention of its exciting causes, and less intensely spasmodic when it does occur. I believe, indeed, that this diminution of nervous irritability is the true explanation of that gradual recovery of young asthmatics which is so common, so almost universal."

6.  Youth asthma is not causes by organic changes:  Lastly, age influences unfavorably the tendency of asthma, not only because it is more apt in advanced life to engender organic disease, but because it is also more apt to have organic disease as its cause. The causation of asthma in youth and age is indeed very different. In age there is commonly some appreciable organic basis for it; in youth much more rarely.

So there you have it: six reasons why the youth are more likely to outgrow their asthma. 


References:
  • Salter, Henry Hyde, "On Asthma: It's Pathology and Treatment," 1882, New York, William Wood and Company, pages 135-142  (original publication of chapters in magazines during the 1850s. The articles were compiled and published as a book, the first edition of which was in 1860 in London)

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