Canine chronic bronchitis. A pathophysiologic evaluation of 18 cases.

Eighteen dogs with chronic bronchitis were studied using physiologic, radiologic, microbiologic, and pathologic techniques. Twelve of these dogs were evaluated before and after two weeks of oral bronchodilator administration. Thoracic radiographs, tidal breathing flow-volume loops, radioaerosol ventilation scans, airway appearance at bronchoscopy, and airway pathology were abnormal in the majority of dogs studied. There was a significant relationship between abnormal ventilation scans and abnormal results for PaO2 and end-tidal airflow. Bronchoscopy revealed excessive mucus and inflammation of airway mucosa in all 16 dogs undergoing this procedure. Endoscopically obtained aerobic bacterial cultures grew mixed bacterial flora in only three dogs. Increased numbers of neutrophils in 14 dogs were detected by airway lavage cytology. A large number of eosinophils were seen in airway lavages obtained from two dogs; these two dogs also had evidence for eosinophilic bronchitis on endobronchial biopsy. Oral bronchodilator administration resulted in clinical and expiratory airflow improvements in most dogs, but had no effect on PaO2 or on the radioaerosol-scan abnormalities. The presence of both the physiologic and pathologic airway abnormalities of chronic bronchitis in dogs presented to a veterinary hospital with chronic unexplained cough was confirmed, suggesting that aerobic bacteria do not play an etiologic role in most cases.