Measurement of respiratory-swallowing coordination using an oronasal facemask in healthy individuals

Respiratory-swallowing coordination (RSC) is well established as an essential airway-protective mechanism. Previous studies have used nasal airflow and/or kinematic rib cage and abdominal measures to assess respiration surrounding swallowing, meaning that the direct influence of oral respiration on RSC remains unknown. This study used a partitioned oronasal facemask to compare respiratory phase patterns measured using isolated nasal airflow with those measured using combined oronasal airflow during non-ingestive and ingestive swallowing tasks. Twenty-four healthy individuals with no respiratory or swallowing disorders were assessed at rest and during cued dry, 10 mL water, continuous drinking and cracker swallowing tasks. Respiratory phase patterns were determined for discrete swallows using the nasal and combined oronasal channels separately. There was variable agreement between respiratory phase patterns according to the nasal and oronasal channels across swallowing conditions. The frequency of exhale-swallow-exhale, inhale-swallow-exhale and exhale-swallow-inhale patterns increased by 2%-3% each with the addition of oral flow data to nasal data, whereas the prevalence of inhale-swallow-inhale and ambiguous patterns decreased. This suggests that estimates of respiratory phase patterns are altered minimally by inclusion of oral respiratory estimates in a healthy sample. There were several additional findings of note, including lower within-participant, within-session trial consistency (test-retest reliability) than expected, suggesting high variability in respiratory phase patterns across trials. Additionally, data showed evidence of swallowing non-respiratory flow at the beginning and end of the respiratory-swallowing pause, moving in both inward and outward directions, potentially expanding current understanding of swallowing non-respiratory flow. Further in-depth physiological investigations are required to improve understanding of these findings.