Narrowing Or Obstruction Of The Bronchi occurs under a considerable variety of different circumstances. It may be the result of inflammation in the bronchial wall itself. There is some swelling of the bronchial mucous membrane in all acute inflammations, and in the case of the finer bronchi, this along with the inflammatory exudation" will cause serious obstruction. Hence, in capillary bronchitis (broncho-pneumonia) respiration is often seriously interfered with.

In Asthma there is an obstruction of the finer bronchi throughout the lungs. It is brought on by nervous agencies, but the exact process-in the bronchi themselves is not quite determined. The nervous origin suggests spasm of the muscular coat of the bronchi, and the suddenness of onset and recovery are consistent with this. There seems little doubt that muscular spasm is the essential element. On the other hand, the long duration of the paroxysms in some cases throws doubt on the view that spasm alone is the cause. An acute hyperemia, due to vaso-motor paralysis and accompanied by oedema, has been suggested as a more probable explanation. From whatever cause there is sudden stenosis of the finer bronchi, spasmodic at the outset, but possibly complicated later on with actual swelling from exudation. Ley den observed, in the sputum of cases of asthma, crystals (sometimes called Leyden's crystals) similar to those found in the blood in leukaemia (Charcot's crystals, see under Leukaemia). He supposes that these crystals may set up a reflex spasm of the bronchial muscles, but this view has not been accepted.

Narrowing of the bronchi may be due to Pressure or Encroachment from without. Tumours not infrequently extend from the root of the lung along the connective tissue around the bronchi, and growing there they may compress and narrow a. bronchus. In not a few cases the tumour infiltrates the bronchial wall, and may even grow through it, so as to present itself in the calibre of the tube, thus narrowing it considerably. These conditions occur chiefly in the case of lympho-sarcoma of the mediastinum. Tumours by their mere pressure, or aneurysms impinging on a bronchus, may narrow the calibre.

Foreign bodies in the bronchi produce obstruction and a large one plugging a main bronchus may lead to serious respiratory trouble. Foreign bodies in the bronchi, however, may give rise to affections of a different kind to be considered in a following page.