Effect of experimental hydrothorax on the cough reflex in conscious cats

The authors induced experimental hydrothorax in cats by injecting dextran into the pleural cavity under brief N2O anaesthesia. They examined the parameters of cough -- elicited by mechanical stimulation of the airway mucosa -- and blood gas and pH values under normal conditions and after the injection of 50, 100, 200 and 250 ml dextran. The tests were always performed 30 min after terminating anaesthesia, i.e. in conscious animals. The free fluid in the thorax was found, in conscious cats, to reduce the inspiratory values of cough, but to have no effect on cough expiration. This is in agreement with previous findings showing that the intensity of a cough expiration does not always depend on the intensity of the preceding cough inspiration. According to this finding, the decrease in the expiratory values of cough observed during experimental pleurisy cannot be due to the actual exudate. In cats, experimental hydrothorax in doses of 200 and 250 ml leads to respiratory insufficiency. The authors further found that, for the study of interoception in the airways of conscious cats, which requires experimental induction of pathological conditions under brief anaesthesia, nitrous oxide is a convenient anesthetic.