Enlarged bronchial glands pressing upon the pneumogastric nerve may cause asthma, and this explains why it is so frequent in children after attacks of measles and whooping cough (Williams and Biermer). Others have remarked that asthma is often coincident with hypertrophied tonsils (Schaeffer). In the great majority of cases the exciting cause does not act directly upon the pneumogastric nerve, but upon the skin or some other remote organ, whence it is transmitted to the nervous centre and reflected back through the nerves of respiration to the bronchi.
Biermer believes that the irritant in many cases, instead of being directly transmitted to the medulla oblongata, causes a fluxion to the exposed mucous membrane. He thinks that the absence of catarrhal symptoms is more apparent than real, the evidences of congestion being unappreciable during the early stages of the disease. According to Riegel,12 the action of the irritant may be explained in one of three different ways—viz. 1st, both the spasm and the fluxion may be the common result of the irritant; 2d, the catarrh may cause the spasm; or, 3d, the spasm may secondarily produce catarrh.
12 Op. cit., p. 256.
Although cold may not be so frequent a cause of asthma as was formerly supposed, low temperature undoubtedly acts as an irritant upon the terminal branches of the respiratory nerves, especially the pneumogastric, and in the manner just described may produce spasmodic contraction of the bronchi. The effect of cold is of course much more deleterious when it is associated with sudden changes and diminished barometric pressure, high winds from the east and north being particularly prejudicial. Aside from its meteorological characteristics, the locality itself exercises a potent influence in the production of asthma; and here, again, we have an example of the capricious character of the disease. A patient who for years has suffered with asthma may change his residence and find immediate relief, but of the special factors which engender the disease in one place and cure it in another we know as yet but little. It is, however, a generally acknowledged fact that removal from the country to a crowded city will often diminish the severity and frequency of the attacks, and English writers mention numbers of cases of asthma which have been permanently cured by a prolonged residence in the foggy atmosphere of London. A very slight change is often sufficient to afford relief, and sometimes removal to another part of the same city is all that is necessary. The town of Aiken in South Carolina is divided by a ravine into two sections: the elevation, soil, and exposure are alike in almost every respect, but persons have been known to suffer severely with asthma on one side and to enjoy perfect exemption from it on the other. A gentleman who resides at Bath in the same neighborhood is perfectly free from asthma at his home, but invariably has an attack as soon as the train begins to cross the Savannah River at Augusta, which is only a few miles distant. More remarkable still is the case mentioned by a French writer of a young man who was unable to sleep in the front rooms of a house without having a paroxysm, but who did not experience the slightest inconvenience when he occupied the back rooms.
Although removal to the city frequently affords relief, there are exceptions to the rule, and many cases are recorded where a change of residence to the country has effected a cure. Ozone, of which but little is as yet known, is supposed by some to be a cause of asthma, and it is not unlikely that the relief afforded by removal to a large city may be partly due to the relatively small proportion of this agent in the atmosphere of crowded localities.
Dust of various kinds, the pollen of plants, certain vapors, gases, smoke, and the emanations from many species of animals, have all been known to excite attacks of asthma. Some persons are so sensitive that the simple act of brushing their clothes is sufficient to bring on a paroxysm. Others are unable to inhale the perfume of roses, lilies, heliotropes, and many other flowers without suffering with an attack. The dust of hay will often cause paroxysms even in those who are not hay-fever subjects. Since Cullen first published the case of an apothecary's wife who had asthma whenever ipecac was powdered in her husband's shop numerous cases of a similar nature have been recorded. Ramadge relates the case of an employé in the East India Company who was compelled to relinquish a lucrative appointment because the smell of tea always provoked a paroxysm of asthma. Many persons are unable to come into close proximity with horses, rabbits, cats, and other animals without suffering, and Austin Flint of New York experienced great inconvenience when absent from home from sleeping upon feather pillows. In his case the asthmatic attack was not brought on by all pillows, but what it was that made one kind more active than another he was unable to determine.
In persons predisposed to bronchial asthma the eating of any indigestible substance may of itself be sufficient to cause an attack, and even an ordinarily full meal, if partaken of late in the day, may have the same effect. Dyspepsia in its various forms and the presence of irritating substances in the intestinal canal are such frequent causes of asthma that they have led to the establishment of several special varieties of the disease—e.g. a. dyspepticum, a. verminosum.
Asthma is frequently due to uterine and ovarian disorders, the so-called a. uterinum.
Voltolini of Breslau has described cases which were evidently due to the presence of naso-pharyngeal polypi, the attacks disappearing with their removal and reappearing with their renewed growth. These statements have been confirmed by subsequent cases observed by Haenisch. Attention has lately been directed to a number of cases in which the asthmatic paroxysm was found to be associated with catarrh of the naso-pharyngeal and laryngo-tracheal mucous membrane. In such cases it is thought that the irritation caused by the pressure of the swollen mucous membrane upon the adjacent nerves is conveyed through them to the pneumogastric, and thus provokes the bronchial spasm. Daly, Roe, Harrison Allen, Hack, and others have traced the paroxysms of hay asthma to an hypertrophied condition of the mucous membrane over the turbinate bones and septum of the nose, which renders it peculiarly susceptible to the action of the irritants which cause that troublesome affection, and have succeeded in curing many cases by simply removing the diseased tissue.
Mental emotion, if sufficiently powerful, may sometimes prevent the occurrence of the asthmatic paroxysm; thus, Steavenson, referring to his own case, states that although subject to frequent attacks he never had one on going up for an examination; and the writer is acquainted with a patient whose attack of hay asthma could frequently be checked by an exciting game of cards.