4. Spasm of the glottis, croup, oedema of the glottis, tracheal stenosis, are all attended with more or less violent attacks of dyspnoea. We are indebted to Biermer for having directed attention to an important symptom by means of which all these affections may be distinguished from bronchial asthma. In the latter, and in all other diseases causing narrowing or obstruction of the finer bronchi, the dyspnoea is during the expiration, but if the impediment be in the larger air-passages the dyspnoea will be during the inspiration. "Dyspnoea during expiration is just as characteristic of narrowing of the finer bronchi as the same condition during inspiration is of croup and other forms of laryngeal stenosis." In croup the neck is extended and the head thrown back. Notwithstanding the violent inspiratory efforts of the patient, the lungs are but partially filled; the air in them becomes rarefied, causing a yielding of the less-resisting parts of the thorax—e.g. the supraclavicular space, the lower portion of the sternum, and adjacent costal cartilages—and a sinking in of the abdomen. During expiration, which is accomplished quickly and with comparative ease, the thorax resumes its natural form. In bronchial asthma, on the contrary, the head is thrown forward, and the shoulders fixed in such a position as to enable the muscles of expiration to work to the best advantage. The thorax, instead of sinking in, is expanded and abnormally round, giving on percussion the peculiar pasteboard-box sound (Schachtelton) which Biermer has described as characteristic of inflation of the alveolæ. In croup the sibilant râles are heard during inspiration, while in asthma they are more pronounced during expiration.
5. Spasm of the diaphragm is another affection from which it may be necessary to distinguish bronchial asthma. This rare disease, which is almost always associated with hysteria, is characterized by a short inspiratory movement, during which all the muscles of inspiration are brought into action, and we have the same sinking in of the more yielding portions of the thorax which has just been mentioned as one of the distinguishing features of laryngeal stenosis. After this the thorax remains fixed for a few seconds, the muscles of inspiration remaining in a state of contraction. There then ensues a quick and powerful expiratory effort, accompanied by a sound not unlike that of hiccough; then another inspiration, with a repetition of the above symptom; and so on until the attack is over. It will be seen from this description that this affection resembles singultus more than asthma, and that there is but little likelihood of its being mistaken for the latter disease.
6. Paralysis of the posterior crico-arytenoid muscles, like croup, spasm of the glottis, and all other affections which produce narrowing of the larger air-passages, is distinguished by the dyspnoea being inspiratory, and not expiratory. The function of the posterior crico-arytenoid muscles being to enlarge the glottis, the result of their being paralyzed would be to lessen the opening through which the air passes to reach the lung; and in viewing the cords in such a case with the laryngoscope it will be found that the opening is reduced to a narrow chink. Another distinguishing feature is that the dyspnoea is continuous, and, unlike bronchial asthma, does not come on in paroxysms.
7. An affection which, like asthma, comes on in the night during sleep is the condition known as nightmare, and, like the former disease, is characterized by labored breathing. To distinguish it, it is only necessary to awaken the patient, when the immediate cessation of all symptoms will at once remove all doubt as to the nature of the affection.
8. Through carelessness or ignorance intercostal neuralgia has been sometimes mistaken for asthma. Pain along the course of the nerve and the presence of the points douloureux, which Valleix has described as characteristic of neuralgic affections, are sufficient to establish the diagnosis.
9. Embolism of one of the middle or larger branches of the pulmonary artery is also characterized by great embarrassment of respiration, but is not likely to be mistaken for asthma by any one at all familiar with the two affections. The cachectic appearance of the patient, the intense anxiety depicted on his countenance, the evidence of cardiac disease or of some affection of the vessels, the weakened cardiac impulse, the thready and at times irregular pulse, together with evidences of more or less pulmonary oedema, are sufficient to distinguish this form of dyspnoea from that of asthma.
PROGNOSIS.—As there is no well-authenticated case of death from uncomplicated asthma, the prognosis quoad vitam may be regarded as absolutely favorable. That death never occurs during the severe paroxysms of asthma may be due to the action of the deficiently aërated blood upon the respiratory centres, and bronchial spasm, causing relaxation when the symptoms have become most threatening. The asthmatic, if his case be incurable, may live for a number of years, and even attain to extreme old age, but his life will be one of intense suffering, which becomes more intolerable as he advances in years. Sooner or later, bronchitis, emphysema, or heart disease is developed, which in its turn may lead to renal disease and dropsy.
Such is the almost invariable result in middle-aged and elderly persons; in the young, however, the chances of recovery are much more favorable. Salter22 states "that in youth the tendency is invariably toward recovery, whereas in one attacked with it after forty-five the tendency is generally toward a progressive severity of the disease and the production and aggravation of those complications by which asthma kills." The favorable result in childhood he attributes to the recuperative power of youth: growth and change, being more rapid than later in life, enable the system to repair during the intervals whatever damage may have been sustained during the paroxysms.
22 On Asthma, Am. ed., p. 168.
There is another class of cases in which, owing to our being able to recognize and remove the cause, the prognosis is quite favorable: thus, if it has been discovered that the disease is due to some local influence, change will often effect a cure, and the patient will remain well as long as he remains in the locality which agrees with him, but generally relapses if he ventures to return to the place where he first contracted the disease. The same may be said of that form of asthma in which the disease is due to some trade or pursuit necessitating the inhalation of irritating dust or gases: the indications are obvious. Cases in which the paroxysms have been traced to the presence of nasal polypi or to a tumor pressing upon the course of the pneumogastric nerve have been promptly cured by the removal of these growths. In all these cases it is presupposed that there is no organic disease, for the presence of any one of the serious complications we have mentioned would dissipate all hope of cure.