Under other, much rarer, circumstances pneumo-thorax occurs in consequence of gas generated in the digestive tract passing into the pleural spaces. The condition then makes rapid progress, and death occurs in a few days.
Fig. 171.—Schema illustrating open pneumo-thorax. Right lung collapsed; pericardium and heart displaced towards the right.
Symptoms. The symptoms are well defined. As soon as the accident occurs the animal exhibits extremely marked and sudden dyspnœa, accompanied by heaving at the flank or general agitation of all the muscles of the body. One of the lungs, in fact, has suddenly been called on to perform the functions of both, and at first it naturally has great difficulty in meeting this demand.
The heaving at the flank and the general agitation of the body muscles is due to the fact that the regularity and rhythm of contraction of the diaphragm are disturbed, and the mechanical conditions have become different on the two sides. From the first, respiration is moaning and expiration becomes rapid, stertorous and deep, while the face is anxious-looking, and the nostrils are dilated as though the animal was on the point of suffocation. On examining the animal from in front or behind, the thorax is easily seen to be wanting in symmetry, the side on which the pneumo-thorax has occurred being immobile as compared with the sound side. The latter, moreover, is dilated in order to compensate for the loss of function of the collapsed lung.
Percussion reveals greatly increased resonance on the side of the pneumo-thorax. On the other hand, the opposite side yields a normal sound.
Auscultation reveals an increase of the respiratory murmur on the side which is still acting and, on the contrary, complete and total suppression of the respiratory murmur on the affected side. On applying the ear to the chest wall, a large soft, amphoric souffle of well-marked metallic character is heard. This is particularly clear on respiration, giving the impression of the existence of a large cavity beneath the ear. The sighing sound heard on auscultation of the chest wall is louder than that heard externally or over the region of the nostrils or larynx; and it seems to be reinforced, as though by the resonance of a large cavity with thin metallic walls. Once or twice per minute, moreover, a sound may be heard like that of dropping water. It is of a very special character, resembling that produced by drops falling to the bottom of a hollow metallic vase, and setting up prolonged vibration.
As secondary symptoms the heart’s action is accelerated, the number of beats rising to 80 or even 120 or 130 beats per minute; appetite is lost; slight tympanites develops as a result of rumination and eructation being suspended; the peristaltic movements of the rumen are interrupted, and constipation develops.
Diagnosis. The diagnosis of pneumo-thorax is easy, and the condition can scarcely be mistaken for any other except diaphragmatic hernia; but the indications derived from percussion and auscultation are so different in the two cases that they need not be further emphasised.
The task becomes more difficult, however, when an attempt is made to identify the exact form of pneumo-thorax, for three principal varieties are recognised.