Korpas J

Influence of simulated mucus on cough sounds in cats

Although in the clinic the presence of mucus in the airways is known to be an important factor influencing the sound of coughing in pathological conditions, this observation has not been established experimentally. We have substituted mucus in the airways of anaesthetized cats with 0.5 ml of natural undiluted egg albumin (EA) from hens eggs, or with 1 ml of 10% pig gastric mucin (PGM) in saline. There were obvious changes in the character of cough sounds and significant increases in the intensity of the sounds (+76% with EA, +36% with PGM). The intensity of cough efforts significantly increased but only in the cats with addition of PGM (mean 30%). Removal of EA or PGM caused the opposite effects, a decrease in cough sounds (-41%) and intensity of cough effort (-52%), with simultaneous changes in the character of the cough sounds. There were no clear-cut patterns of cough sounds as has been described for humans. The cough sounds were often present not only during the expiratory phase of cough but also during the inspiratory phase. The results establish an important role of mucus in the airways in the creation of cough sounds.

Effect of experimental lung oedema on cough sound creation

We have assessed the importance of changes in lung structure on the pattern of cough sound and its creation with 13 anaesthetized cats. Acute lung injury with oedema was induced by i.v. administration of a mixture of fatty acids. Cough was elicited by mechanical stimulation of the mucous membranes of the airways and was evaluated by its intensities of effort and sound before and up to 2 h after administration of the fatty acids. Changes of cough sound pattern were not definitive, there being no typical alterations. The cough effort and sound intensities, induced from the trachea, consistently decreased (by 70-80% in both cases). The cough efforts immediately after induction of oedema were transiently abolished in some cats. The cough values induced from the larynx similarly decreased at 5 min (51-57%) but subsequently gradually returned to control values. There were significant correlations, both for coughs induced from the trachea and from the larynx, and for changes in intensity of efforts compared with sounds. Thus, pathological changes in the lungs modify the intensities both of cough efforts and their associated sounds.