Steavenson,[11] who inherited asthma from his grandfather, his father's
generation having been entirely free from the disease. In other cases
it may alternate with some other neurosis or with gout or rheumatism;
for instance, the children of an asthmatic father may be epileptic or
gouty and the grandchildren asthmatic, or the asthmatic tendency may
develop in one child of an asthmatic family and the gouty diathesis in
another. It is by no means necessary for the hereditary transmission of
the disease that the father should be asthmatic when the child is
conceived, as there are many cases recorded in which asthma developed
in children whose fathers had completely recovered before they
contracted marriage and never had any subsequent return of the disease.
[Footnote 11: W. E. Steavenson, _Spasmodic Asthma_, London, 1882, p.
8.]
All authorities agree that asthma is much more frequent among males
than females. Of Théry's cases, 60 were females and 80 males. The more
recent statistics of Salter show that the males exceed the females in
the proportion of two to one. This undue frequency of a purely nervous
disease among males appears at first to be at variance with the
generally-received opinion that such affections pertain rather to the
female sex; but on investigating the ages at which the attacks first
come on it will be found that between the fifteenth and thirtieth
years--that is, during the period when sexual function is most
active--the proportion is reversed, females being attacked much oftener
than males.
Asthma occurs more frequently in childhood than at any subsequent
period--a fact which may be explained by the great susceptibility of
young children to catarrhal affections of the air-passages and to the
frequent occurrence at that age of measles and whooping cough (Salter).
Of 225 cases collected by Salter, 71 occurred before the tenth year,
and of these, 10 began during the first year, the youngest of them
being only fourteen days old at the time of {191} the attack. From ten
to twenty it occurs less frequently than at any other period of life,
but from that age to the fortieth year there is a steady increase in
the number of cases. During the next decade, from forty to fifty, the
disease diminishes in frequency, and from that period on the number of
cases continues to grow smaller and smaller with advancing years,
comparatively few commencing after the fiftieth year.
The following tabular statement, compiled by Salter, shows the
comparative frequency of asthma during the various periods of life:
From 1 to 10 years, 71 cases. | From 40 to 50 years, 24 cases.
" 10 to 20 " 30 " | " 50 to 60 " 12 "
" 20 to 30 " 39 " | " 60 to 70 " 4 "
" 30 to 40 " 44 " | " 70 to 80 " 1 "
These figures demonstrate the fallacy of the popular idea that old
people are especially liable to asthma. Its prevalence during the later
periods of life is due to the fact that while, on the one hand, the
affection rarely causes death, on the other it is scarcely ever curable
except during childhood, and thus the cases contracted at different
ages accumulate and form a large aggregate as life advances.
Those cases occurring in childhood and late in life are likely to be
associated with more or less bronchial catarrh, while those which come
on when the body has attained its fullest development are almost
invariably purely nervous in character.
The period of life at which asthma commences is an important element in
the prognosis of the disease, the cases occurring in early childhood
being likely to end in recovery, while those coming on later in life
are exceedingly protracted in their course and liable to lead to
organic diseases of the heart or lungs.
Asthma does not appear to be influenced by the seasons, some authors
claiming that it is most frequent in summer, while others maintain that
the greatest number of cases occur in winter.
Exciting Causes.--Bronchial asthma being a neurosis of the
pneumogastric nerve, its exciting causes may be divided into those
which act upon the nerve directly, and those which are reflected from
more remote parts or organs.
In the first class the irritant may act upon the nerve at its origin in
the medulla oblongata or upon some part of its continuity. Various
poisons, organic or inorganic, when introduced into the system may so
change the character and composition of the blood as to interfere with
the nutrition of the respiratory centre, and thus cause more or less
embarrassment of respiration; but the attacks of dyspnoea due to these
causes are more continuous than those of ordinary asthma, and are
wanting in many of the symptoms which we have described as
characteristic of that disease. These forms of dyspnoea are usually the
result either of some constitutional disease or of some poison
introduced into the system, both of which act by diminishing the
proportion of red corpuscles in the blood. Of this we have examples in
the dyspnoea sometimes observed in syphilis and malarial fever and in
lead and mercurial poisoning--the so-called a. saturninum and a.
mercuriale. It is true that there have been instances in which the
paroxysms of asthma have come on at regular intervals and have yielded
to quinine, but it is not regarded as proved that such cases were due
to malarial poisoning (Sée).
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 {192} 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.
[Footnote 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 {193} 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.
Asthma, like other neuroses, is much more frequent among the educated
and refined than among the coarser and more ignorant classes of
society, and those leading luxurious lives are more liable to the
disease than those of simple and frugal habits. Of the various
professions, those which involve much exertion of the voice furnish the
largest contingent; hence it is common among public speakers,
clergymen, and lawyers.
In former days the retrocession of cutaneous eruptions was supposed to
play an important rôle in the production of asthma, but of late years
this theory of causation has found but few advocates among intelligent
physicians, the only author of any prominence who still adheres to it
being Waldenburg, who has proposed to designate such cases as a.
herpeticum.
PATHOLOGY.--We have elsewhere alluded to the various theories with
which the older writers endeavored to explain the phenomena of asthma,
and need not here refer to them again.
The first step toward a truly scientific theory of the pathology of
asthma was the discovery by Reisseisen of the smooth muscular fibres of
the bronchial tubes. These fibres are found not only in the large and
medium-sized bronchi, but even in those of the smallest calibre,
Kölliker having {194} demonstrated them in bronchioles 0.18 millimeter
in diameter. It was ascertained by Williams that by irritating the lung
he could cause contraction of these fibres, and Longet subsequently
proved that the same effect could be produced by galvanizing the
pneumogastric nerve. Guided by these important discoveries, most modern
pathologists have arrived at the conclusion that bronchial asthma is a
spasmodic contraction of the middle and finer bronchi, dependent upon
some derangement in the function of the pneumogastric nerve. This, the
so-called spasmodic theory, is not entirely new, Willis, as we have
before stated, having described as early as 1682 a variety of asthma
which he believed to be the result of a "spasmodic action of the
muscles and nerves of respiration," and to which he applied the term
"asthma convulsivum." Although revived from time to time, it was not
until some two hundred years later, and after Romberg had definitely
settled the question of the essential character of the disease, that
the spasmodic nature of asthma received general recognition. Bergson
adopted it in his prize essay in 1840, and ten years later it found a
warm supporter in the person of Hyde Salter, whose valuable
contributions have added so much to our knowledge of bronchial asthma.
The theory that asthma is due to spasm of the bronchial muscles met
with but little opposition until 1854, when Wintrich, after a series of
experiments, arrived at conclusions directly opposed to those of
Williams and Longet in regard to the contractility of the muscular
fibres of the bronchi, and refused to accept the spasm theory on the
ground that it afforded no rational explanation of the phenomena of
asthma. He believed that the various symptoms of that disease were due
to tonic spasm either of the diaphragm alone or of the diaphragm and
the other muscles of respiration. These experiments of Wintrich were so
carefully conducted, and his standing as a specialist in respiratory
diseases so high, that his theory found many supporters, and might
perhaps have been generally accepted had it not been for the
distinguished French physiologist, Paul Bert, who in 1870, with
improved methods of scientific research, succeeded in demonstrating
that Williams and Longet were after all correct in their statements as
to the contractility of the bronchial muscles.
One of the most zealous advocates of the spasm theory of asthma, and at
the same time its most learned expositor, is Biermer,[13] whose
classical lecture on that disease, which appeared a short time after
the publication of Bert's experiments, is perhaps the most satisfactory
work ever published on the subject. He defines bronchial asthma as a
"neurosis depending upon tonic spasm of the bronchial muscles and
caused by faulty innervation of the pneumogastric nerve." He claims
that this theory is confirmed by clinical experience--that the
suddenness with which the attack comes and disappears, and the long and
forced expiration with the sibilant râles and other evidences of
stenosis which accompany it, admit of no other explanation. In support
of this view he calls attention to the rapidity with which the paroxysm
yields to chloral, all of its symptoms disappearing within from five to
ten minutes after the administration of a moderate dose of that agent.
Wintrich and his supporters, besides denying the contractility of the
bronchial muscles, object to the spasm theory that the distension of
the thorax and descent of the diaphragm, both constant symptoms, are
incompatible with spasmodic closure of the bronchial tubes, and that
constriction from such cause by impeding the entrance of air into the
alveolæ would be more likely to cause diminution in the size of the
thorax than its enlargement, and that the diaphragm, instead of
descending, would be drawn upward. Biermer acknowledges that this to a
certain extent is true, and concedes that constriction of the tubes
would interfere with both acts of respiration, but claims that it does
not do so {195} to the same extent in the two movements. The spasmodic
constriction acts as a sphincter which is readily overcome during
inspiration, but prevents the escape of air during expiration, the
latter movement being slower and less complete than the former. Were
the expiratory pressure exerted upon the contents of the alveolæ alone,
it would readily overcome the spasmodic constriction of the bronchi,
but it also compresses at the same time the bronchioles. "When the
bronchi are spasmodically contracted, they are subjected during
expiration to the general pressure of that movement plus the pressure
of the spastic contraction of the bronchial muscles. The walls of the
bronchioles being soft and compressible, the expiratory pressure,
instead of overcoming the obstruction and opening them, would tend to
close them all the more tightly." He calls attention to an analogous
condition which obtains in capillary bronchitis, when, owing to
swelling of the mucous membrane and to the accumulation of secretion in
the tubes, the alveolæ are cut off. Here, too, the expiratory pressure
is often sufficiently powerful to overcome the obstruction, but if
under these circumstances it is too feeble, collapse of the lung
ensues. When, on the other hand, the inspiration is strong enough to
overcome this obstacle, air enters the alveolæ, and, being imprisoned
there, causes inflation of the air-cells as in asthma. That collapse of
the lung does not occur in the latter disease is due to the fact that
the inspiratory act is always sufficiently powerful to overcome the
spastic contraction of the bronchioles.
[Footnote 13: A. Biermer, "Ueber Bronchial Asthma," _Sammlung
klinischer Vorträge_, No. 12, Leipzig, 1870.]
The air entering the lung during inspiration is pent up by the spastic
constriction of the bronchi, which, acting as a valve, admits of its
passage in one direction, but impedes its escape during expiration, and
thus causes inflation of the air-cells and insufficient aëration. Owing
to the distension of the alveolæ the thorax is expanded and the
diaphragm forced downward. A tetanic spasm of the diaphragm lasting for
hours, such as that which Wintrich describes, and with which he
endeavors to explain the descent of that muscle as well as the other
symptoms of asthma, is not only improbable, but is contrary to clinical
experience. If the diaphragm were thus spasmodically contracted, it
would remain fixed in one position, but Biermer has demonstrated that
there is more or less rhythmic movement of that muscle even during the
paroxysm; but if no movement of the diaphragm were observed, it would
still be no proof of tonic spasm of that muscle, as its immobility
might be due to other causes. According to Biermer, the inflation of
the lungs and their insufficient ventilation afford a satisfactory
explanation of the most important symptoms of asthma, as Breuer[14] has
shown, in his paper on the automatic regulation of respiration through
the pneumogastric nerve, that various embarrassments of respiration
must be corrected by some suitable modification of the act itself;
hence when, as in asthma, the lung is unable to empty itself, the
expiratory act must be strengthened and prolonged to overcome the
obstruction occasioned by the spasmodic constriction of the bronchial
tubes; whereas incomplete filling of the lung would necessitate
increased inspiratory effort. According to Biermer, "expiratory
dyspnoea is as characteristic of obstruction of the finer tubes," be it
from spasm, as in asthma, or from stoppage with viscid mucus or from
swelling of their lining membrane, as in bronchitis, as the same
condition during inspiration is of narrowing of the larger
air-passages--an important point in differential diagnosis to which we
shall again have occasion to refer. He is unable to explain the
relationship between bronchial spasm and catarrhal hyperæmia of the
air-passages, but believes that it may be accounted for as follows:
"Either the bronchial fluxion causes the spasm--that is, that there
exists between them a causal connection--or the hyperæmia and the spasm
are the {196} joint effect of the exciting (centripetal) nerves; in
other words, both are due to reflex action."[15]
[Footnote 14: "Die Selbsterneurung der Athmen durch den N. vagus,"
_Sitzungsbericht der K. K. Akademie der Wissenschaften zu Wien_, Bd.
lviii. Abtheilung ii., Nov., 1868.]
[Footnote 15: In presenting Biermer's theory the writer has drawn
freely upon that author's well-known lecture on "Bronchial Asthma," as
published in _Volkmann's Sammlung klinischer Vorträge_, _loc. cit._]
Another explanation of the phenomena of asthma is that proposed by
Lebert,[16] who, although he concedes that bronchial spasm is an
all-important factor, denies that it of itself is sufficient to account
for the sudden and enormous inflation of the lungs observed in that
disease. He doubts the possibility of a valvular closure of the
bronchi, as claimed by Biermer, but believes that the bronchial spasm,
which he regards as primary, causes secondary spasmodic contractions of
the diaphragm and of the inspiratory muscles of the neck and chest. The
spasm of the diaphragm he believes to be tonic in its character, but
not continuous, thus meeting Biermer's objection to the Wintrich
theory, that tonic spasm of that muscle lasting longer than a few
minutes would inevitably cause fatal asphyxia.
[Footnote 16: _Klinik der Brustkrankheiten_, 1ster Band, 2te Hälfte, p.
438.]