Bronchial asthma is a chronic inflammatory disease of the respiratory tract in which mast cells (TK), eosinophils and T-lymphocytes take part; this disease is characterized by repeated episodes of wheezing, shortness of breath, chest pain, coughing, especially at night and / or early morning; such symptoms are accompanied by widespread variable reversible obstruction of the bronchial tree, resolving spontaneously or under the influence of treatment.
The most complete morphological data on the condition of the bronchi and lung tissue were obtained during autopsy of patients who died at the height of an asthmatic attack. In this case, acute bloating of the lungs, often combined with emphysema, is detected macroscopically, the lungs perform the entire chest cavity, very often rib prints are visible on the surface of the lungs. The height of the diaphragm is determined, as a rule, at the level of the 6th rib.
The surface of the lungs is usually pale pink in color, in the section – dark or gray-red. Pneumosclerosis, as a rule, is mild. A thickening of the bronchial walls protruding above the surface of the incisions is revealed; almost all bronchial generations up to the respiratory bronchioles are filled with thick grayish-yellow glassy molds of sputum (bronchial secretion), which are squeezed out in the form of thin “worms”.
The mucous membrane of the bronchi is hyperemic almost throughout. As a rule, pulmonary edema is pronounced, sometimes thromboembolism of the pulmonary artery and / or its branches occurs. During a histological examination, in the expanded lumens of the bronchi, mucous plugs, layers of desquamated epithelium with an admixture of neutrophils, eosinophils, lymphocytes, almost complete exposure of the basement membrane are determined, sometimes Charcot-Leiden crystals are found. In the preserved epithelium, an increased number of goblet cells.
Infiltrates in the walls of the bronchi consist mainly of eosinophils. Expand and sharp plethora of capillaries of the mucous membrane and submucosal layer. The basal membrane is usually unevenly thick up to 5 μm, separate passages are often visible in it, perpendicular to the lumen of the bronchus, focal resorption of individual sections of the basement membrane. Currently, they believe that this is a consequence of the action of the eosinophilic kaionic and basic alkaline proteins! eosinophils.
According to immunomorphology, the concentration of globulins, type II, III, IV collagens, fibronectin produced by proliferating fibroblasts is increased in thickened areas of the basement membrane. In addition, a diffuse arrangement of serum albumin and fibrinogen was observed in the basement membrane. Electron microscopy showed that the basement membrane consists of two components: the basement membrane itself, 0.8 μm thick, which is separated from the epithelium by a light zone 0.6 μm thick, and the wide zone adjacent to the stroma, which consists of collagen and thin parallel fibers. Most researchers believe that the thickening of the basement membrane is associated with the deposition of immune complexes.
The submucosal layer is densely infiltrated by polynuclear cells and eosinophils almost throughout its length. There is a pronounced edema of the stroma plethora of dilated capillaries. Hyperplasia of the glands and their overflow with SHIK-positive material are revealed. Regarding the state of the muscle membrane, the data are contradictory. Some authors report hypertrophy and dystrophy of myocytes, however, with a morphometric study, bulk density often does not differ from control values, which is associated with severe wall edema.
In the peripheral lung tissue, there is a marked expansion of the respiratory bronchioles, alveolar passages and alveoli, intra-alveolar and interstitial edema is determined, a small number of alveolar macrophages and eosinophils are found in the lumens of the alveoli. The changes described above are found, as a rule, in those who died with a history of bronchial asthma for no more than 5 years. In patients with a long history of AD, elements of chronic productive inflammation are mixed with changes in the bronchi and lung tissue.
Based on the study of bronchobiopsy, a number of studies of recent years have allowed to assess the condition of the bronchial wall in the interictal period. These changes are similar to changes in the bronchi in experimental models in the interictal period. Currently, there is evidence that when analyzing the material of bronchobiopsies, an assessment of the phase of the disease is possible. It has been shown that cells of the desquamated epithelium, Creole body, associations of neutrophils, lymphocytes and eosinophils are found in the lumen of the bronchus. The number of goblet cells increased, the basement membrane was thickened, glandular hyperplasia, expansion and plethora of the vessels of the submucosal layer were detected, the number of eosinophils, lymphocytes, neutrophils and TK, single eosinophils in the epithelium were increased in the thickness of the wall.
The condition of the muscle membrane is not always the same. Hypertrophy and muscle cell contractures are often observed, but this is an unstable symptom, sometimes muscle cells are found in a state of granular or fatty degeneration.
Some controversial questions remain about the morphology of individual wall elements. Until now, there is only one criterion for bronchospasm – the detection in the lumens of the bronchi of mucus-filled layers of desquamated epithelium. In the experiment, another sign of bronchospasm was discovered – a circular displacement of the cartilaginous plates and their entry one after another. In earlier publications, corrugation of the epithelial layer in the form of an “asterisk” and the perpendicular arrangement of rounded bundles of muscle fibers were taken as a criterion of bronchospasm, however, these changes are also found in other deceased patients in the absence of a bronchospasm clinic.
Since bronchospasm is one of the triggers of asthma and reoccurs in the late stage of an attack if there are already mucous plugs in the lumen, the section, which is usually performed 6 hours after death, when rigor mortis is already resolving, shows reliable signs of bronchospasm detect almost impossible. It is likely that early autopsy within the first 2 hours after death will reveal reliable criteria for bronchospasm.