Procedure
cough, visual and auditory
Liquid solutions of EB (Sigma-Aldrich, CAS No. 105-54-4) were diluted in paraffin oil (Sigma-Aldrich, CAS No. 8012-95-1) at 20%, 40%, and 60% v/v concentrations, with a total volume of 10 mL prepared in 1-oz straight-sided glass jars (Uline). EB was delivered using a computer-controlled, eight-channel olfactometer (see Experimental setup. (A) Outside view of the eight-channel, computer-controlled dynamic dilution olfactometer that delivers chemical stimuli. (B) Spirometer differential pressure transducer connected to a pneumotach flow head and face mask. (C) Calibration syringe. (D) Data acquisition hardware unit that records and digitizes airflow signals. (E) Inside view of the olfactometer.Prior to the experiment, participants were initially exposed to EB in ascending order of low to high concentrations until an audible cough was produced. This task familiarized participants with the stimuli, ensured they were comfortable with the task, and determined if they demonstrated a cough response to EB. Next, all participants received standardized verbal instructions from the research team about the experiment. Participants were instructed that they would inhale a stimulus through the silicone face mask and were explicitly told to “cough directly into the face mask,” which was connected to a pneumotachograph (see Baseline experimental testing involved the presentation of three EB concentrations in triplicate in a randomized and blinded manner, resulting in a total of nine trials. During trial presentations of the stimuli, participants attended to a computer monitor while wearing the silicone face mask that provided visual and auditory prompts to inhale on a countdown to synchronize the temporal delivery of the stimulus. An auditory tone was presented for 3 s while the chemical stimulus was delivered to participants, at which time participants inhaled for 3 s. No prompts to exhale were provided. Following the stimulus delivery, no subsequent computer prompts were provided about the duration or rate of inhalation or exhalation. Participants continued to breathe through the face mask while making sensory ratings. To reduce the effects of sensory adaptation between trial presentations, participants breathed room air without the face mask for a minimum of 60-s intervals as previously described (To further investigate our cough paradigm, we tested whether the implementation of breath control influenced cough. Following a 10-min break outside the testing room to reduce the effects of sensory adaptation to EB, participants were randomized to one of two breath control conditions: PLB (