Comparison of Cough Assessment by Visual and Airflow Changes in the Guinea Pig Model of Citric Acid-Induced Cough

Abstract

Introduction: Cough is a common respiratory complaint associated with decreased quality of life; however, effective antitussives are limited. Guinea pigs are widely used to assess the efficacy of novel treatments; the cough response is detected by visual observation and methods based on characteristic airflow changes. However there are limited details on how these two methods of cough assessment compare. The objective of this study was to use the guinea pig cough model to compare visual assessment with cough software (EMMS, UK).

Methods: Studies were performed in male guinea pigs (8 or 10/group). Animals were exposed to citric acid (0.2 to 0.8M) or following pre-exposure to 0.6 mM histamine/0.2 M citric acid (enhanced cough) using whole body plethysmography chambers. Airflow signals were acquired and analysed using eDacq software (EMMS);cough was assigned on the basis of 8 cough templates. Codeine was administered (up to 60 mg/kg, oral) as a positive control reference item.

Results: Visual and automated cough counts were significantly correlated in the cough and enhanced cough protocols (p<0.01). However, Bland-Altman plots showed the EMMS coughs outnumbered manual coughs when coughing frequency increased above 40. Different cough templates were generally evenly distributed in cough and enhanced cough studies. During cough, respiratory rate remained unchanged while PenH and peak inspiratory/expiratory flow increased (P<0.01). Codeine significantly reduced cough and respiratory parameters changes (P<0.01).

Conclusion: Cough assessment based on characteristic airflow changes is an objective method of cough enumeration in the guinea pig model of citric acid-induced cough.