Equipment
cough, Cough
Acoustic and aerodynamic recordings will be carried out.Acoustic equipment: The acoustic recordings will be made simultaneously using a skin-contact microphone (Albrecht AE 38 S2) and a professional quality acoustic free-standing microphone (AKG Perception 420 Omnidirectional). The intensity in dB will be recorded by an external sound level metre (Bruel and Kjaer 2236). The free-standing microphone and the external sound level metre will be placed at 40 cm to the right of the mouth of the participant. Only the skin-contact microphone will be used to record induced reflexive coughs because of the presence of the anaesthesia facemask through which citric acid will be delivered (see more details in section (B) Aerodynamic equipment). Natural reflexive coughs and sustained vowels [a] produced by HNC patients during FEES will be recorded with the skin-contact microphone only to avoid the recording of environmental or equipment noise. Acoustic cough and voice signals will be recorded with an HP ProBook computer (Hewlett-Packard Company, USA) using the computer program PRAAT and the preamplifier 2-channel interface Presonus Audiobox USB 96 Audio, with a sampling frequency of 44.1 kHz.Aerodynamic equipment: The aerodynamic recordings will be carried out with an anaesthesia facemask connected to a spirometer Pocket-Spiro USB (Medical Electronic Construction, M.E.C, Belgium). Cough will be induced using a differential pressure transducer with a one-way inspiratory valve for a nebulizer connection. The nebulizer will deliver citric acid during a 2-s inspiration. Each participant will complete a maximum of 5 challenges of increasing concentrations of citric acid: saline, 30 mM or 5.8 mg/ml citric acid, 100 mM or 19.2 mg/ml citric acid, 300 mM or 58 mg/ml citric acid and 1000 mM or 192 mg/ml citric acid as described in Janssens et al. [