In both cases the pulmonary tissue is pale, the blood-vessels are partially obliterated by compression; circulation and aeration of the blood are impeded—hence the appearance of the disturbance noted.
Causation. Emphysema is seen in adult working oxen; also, and to an even greater degree, in aged cows. It is produced by excessive strains in draught, or more often by the paroxysms of coughing so common during simple or parasitic bronchitis, broncho-pneumonia, pneumonia, chronic broncho-pneumonia, etc. Successive gestations also produce it.
All these pathological conditions also interfere with the nutrition of the bronchial mucous membrane, particularly of its deep-seated muscular layer, which is then incapable of regulating the distribution of air in the bronchial channels. The distribution being no longer regulated by reflex action, air accumulates at certain points as a result of the expiratory efforts made during coughing, and dilatation of the vesicles or lobules occurs.
Diseases of the digestive apparatus, acute or chronic tympanites in particular, may play a certain part by compressing the diaphragm, causing expiratory efforts and fits of coughing.
Furthermore, swelling of the lymphatic glands at the entrance to the chest, by compressing the pneumo-gastrics, provokes reflex cough and finally emphysema.
Symptoms. Pulmonary emphysema is marked by accelerated respiration due to diminution in the respiratory capacity, which is often very seriously affected; to insufficient absorption of oxygen in consequence of diminution in the space available for exchange of gases in the lung, and to insufficiency of expiration. This acceleration in breathing, though little marked during repose, becomes very pronounced after exercise, or during hot weather; and under these circumstances is accompanied by a paroxysmal, feeble but shrill cough, without discharge. This cough without discharge is frequently followed by swallowing.
Percussion reveals an important point, viz., increase in the normal resonance of the thorax.
On auscultation the vesicular murmur is found to be diminished, the respiration assumes a rough and rasping character, inspiration is difficult, expiration painful, and often divided into two periods, as indicated by a slight double movement of the flank. Expiration is clearly audible. Its duration is generally less than that of inspiration, although in some cases it is equal or even longer. It is accompanied by sibilant and snoring râles, sometimes even mucous râles, of an intermittent character. In rare cases there may be difficulty of respiration, as in broken-winded horses.
Diagnosis. The diagnosis may suggest a doubt as to whether emphysema or tuberculosis is present, but in the latter there is fever, the general condition is poor; on percussion the thorax reveals areas of partial dulness; and expiration is rough and prolonged, sometimes of a blowing character, a peculiarity which is exceptional in emphysema.
Prognosis. The prognosis is not very grave, except where emphysema is only an accompanying symptom of another disease, such as chronic bronchitis, tuberculosis, etc.