Tracheal Collapse and Chronic Bronchitis as a Cause of Coughing in Dogs with Endocardiosis

Introduction. Chronic coughing in dogs of small breeds older than 8–10 years is a complex diagnostic and therapeutic problem. These dogs are often diagnosed with heart murmurs caused by mitral valve degeneration (endocardiosis), and many of them also suffer from respiratory tract diseases. Thus, cough may be the result of one of the several different pathophysiological mechanisms. However, the available literature does not provide data on the incidence of inflammation processes in respiratory tract of dogs with tracheal collapse and endocardiosis. The aim of this research is to determine the presence or absence of respiratory tract infections or inflammations in dogs with tracheal collapse and compensated endocardiosis.

Materials and Methods. Dogs with asymptomatic endocardiosis, chronic cough, moderate tracheal collapse and moderate congestion in pulmonary circulation were selected for the study. A total of 27 dogs of small breeds met these criteria. All dogs underwent a complete blood count, serum biochemistry profile test, urine analysis, radiography of the neck and chest in three projections. The criteria for excluding dogs from the study were detection of decompensated heart diseases, neoplasms or systemic diseases, as well as X-ray detection of any patterns other than bronchial pattern and that indicating the tracheal collapse. In the absence of contraindications to anaesthesia, bronchoscopy and bronchoalveolar lavage (BAL) were performed under anaesthesia for further assessment of tracheal collapse degree. The sample obtained with BAL underwent cytological and bacteriological examination. The collapse of trachea and of all visible bronchi was assessed in a subjective way as absent, mild, moderate or severe. The degree of tracheal collapse was determined in accordance with a pre-specified scheme based on the percentage of the tracheal or bronchial lumen diameter reduction at its narrowest point from 50% to 30% of its estimated diameter.

Results. Along with the neutrophilic inflammation present in most dogs, mixed and lymphocytic inflammations were also diagnosed. The cytological analysis of BAL fluid revealed that non-degenerate neutrophils were the predominant cells in 13 dogs (48%); macrophages (15%) were the predominant cells in 4 dogs; and lymphocytes (11%) were the predominant cells in 3 dogs, corresponding to neutrophilic, macrophage and lymphocytic inflammations, respectively. In three dogs with neutrophilic inflammation, the degenerative changes in neutrophils and phagocytic bacteria were observed, and inoculation to medium resulted in isolation of Escherichia coli in 2 dogs and Klebsiella pneumoniae in 1 dog. Aseptic mixed inflammation was observed in 7 dogs (26%).

Discussion and Conclusion: Aseptic inflammation of the respiratory tract was common in a group of dogs with subclinical endocardiosis and moderate tracheal collapse. The main cause of coughing remains unclear, whether it is caused by the collapse of the upper respiratory tract or persistent aseptic inflammation? Further research, observation and control over inflammation in dogs with endocardiosis are needed.

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