Another frequent concomitant of the emphysematous lung is a dilatation of the right cavities of the heart, especially the auricle, and an attenuation of their walls. The same condition is noticed in pulmonary emphysema in man and like this is probably due to the slow and imperfect circulation in the diseased lung.
Collating these structural changes with the different causes of the disease we find that they harmonize with the theory of impaired function on the part of the vagus nerve or its presiding ganglia, whether this functional disturbance has its origin in disorder of the digestive organs, as in the great majority of cases, in severe muscular efforts, or in chronic bronchitis.
Section of the vagi nerves affords an exaggerated instance of their paralysis and its results. These are mainly emphysema, capillary dilatation, blood extravasation, inflammation and pulmonary collapse. Emphysema is the first result and due to the slow, deep respiration (Boddaert) and loss of contractibility (Longet); capillary dilatation results from the extreme distension of the air cells and the retention in them of air highly charged with carbonic acid (Donders); the other lesions occur later and own very different causes.
That this is the true nature of the disease would further appear from the occurrence of emphysema without broken wind, two cases of which are recorded by Percivall; and from the existence of broken wind without emphysema. Cases of this last variety have been recorded by Godine, Volpi, Rodet, D’Arboval, and Delafond in France; and by Sewall, Dick, Smith, Hallen and Gloag in Britain. In connection with this last class of cases it must be noted that dilatation of the right cavities of the heart sometimes gives rise to very similar symptoms, and that the signs of chronic bronchitis are often scarcely distinguishable from those of broken wind. In catarrhal bronchitis too, after the air tubes have been washed, it is sometimes impossible to decide whether the lining membrane has been the subject of inflammation or not.
Symptoms. The most prominent are the double lift of the flank with each expiratory act, in the absence of fever, the short, weak, dry and almost inaudible cough, the wheezing noise in breathing when that is accelerated by exertion, and the intestinal flatulence with the frequent passage of gas.
The cough usually heralds the advent of other symptoms. Often the character of the cough draws forth the remark that an animal is becoming broken winded and though no other symptom is seen at this time they thereafter rapidly develop themselves. At this early stage of the disease the cough is paroxysmal, coming on in fits during work or after a drink of cold water. Once the disease is established the horse rarely coughs more than once at a time. The cough is extremely short, weak and low and followed by a sort of wheeze. So specific is it that if once heard it can readily be recognized. The sudden effort made in coughing usually leads to the expulsion of gas from the flatulent bowels.
The double lifting of the flank in expiration is not peculiar to broken wind. It is seen as well in most diseases of the lungs and even of other organs (enteritis, peritonitis) which interfere with the freedom of the respiratory act. If however it is not attended by fever but associated with the broken winded cough, the wheezing respiration, the disordered and flatulent state of the bowels, the tumultuous beating of the heart against the left side after exertion, and the slight flow of clear, watery matter from the nose, it is pathognomonic. The act of inspiration is quick and free, that of expiration is not uniform and continuous as in health, but consists of two stages interrupted by a momentary arrest. In the first stage the posterior part of the abdomen is slightly raised and it falls in laterally; then comes an almost imperceptible period of inaction, followed at once by the further lifting of the flanks to complete the expulsion of air from the lungs. The first stage seems the natural collapse of the walls of the chest and forward movement of the diaphragm, the second a contraction of the abdominal muscles partly due to an exercise of will to overcome the obstacle to the expulsion of air.
In very bad or advanced cases these symptoms are more marked. The inspiration is sudden and manifested by a rapid expansion of the chest, and dropping of the belly previously supported by active contraction of the abdominal muscles. The two stages of the expiratory act are quite distinct. The first is manifested by a sudden falling in of the walls of the chest so that the ribs no longer stand out prominently beyond their interspaces; the abdomen equally rises inferiorly and falls in laterally so that a projecting ridge is formed from the lower end of the last rib to the point of the hip. This is specially marked during the period of inaction, and this is succeeded by the second effort quick and almost convulsive. These movements are so extensive that they are conveyed in a striking degree to any vehicle to which the animal is attached, especially if it has only two wheels, and a rider on horseback feels the movement still more disagreeably. When a horse is in this state the alternate rising and falling of the abdominal organs imparts a synchronous movement of protrusion and contraction to the anus and in thin subjects a rising and falling of the muscles on each side of the root of the tail. The nostrils too are kept constantly dilated.
There is a nasal discharge, but this is very inconsiderable in the early stages of the malady. It is a clear watery or slightly grayish albuminous material without any visible admixture of pus globules, and on drying it leaves a scarcely perceptible crust. At first it appears intermittently and in minute quantities, but in bad cases it becomes almost constant, and is especially profuse after exercise.
Abnormal respiratory sounds are marked symptoms in the advanced stages. The wheezing noise of the breathing, especially when that is excited by exertion, may be heard at a short distance from the animal. The increased resonance on percussion along the lower border of the lung is only heard when the emphysema is extensive. The dry sibilant or whistling râle heard over the same parts is equally a symptom of the advanced stages. When there is much discharge a moist rattle is often heard over the lower end of the windpipe or immediately behind the middle of the shoulder. The overlaying of the anterior lobe by the thick, muscular shoulder, and the complication of results obtained at the free border of the lung by the abdominal noises and resonance render these results less conclusive in the earlier stages and slighter cases.