ObjectiveThe primary objective of this study was to evaluate the impact of high-flow nasal cannula oxygen therapy [HFNC] on the diaphragm thickening fraction. DesignProspective, descriptive, cohort study SettingThe study was conducted in the Physiology and Respiratory Care Laboratory, Intensive Care Unit, Hospital Británico de Buenos Aires. ParticipantsThirteen healthy subjects >18 years old InterventionsHigh-flow nasal cannula oxygen therapy Main variables of interestDemographic data (age and gender), anthropometric data (weight, height, and body mass index), and clinical and respiratory variables (Diaphragm thickening fraction [DTf], esophageal pressure swing, respiratory rate [RR], esophageal pressure-time product per minute [PTPes/min]). ResultsMedian DTf decreased significantly as flow increased (P<.05). The baseline DTf measurement was 21.4%, 18.3% with 20 l/m, and 16.4% with 40 l/m. We also observed a significant decrease in RR as flow increased in HFNC (P<.05). In the 8 subjects with recordings, the PTPes/min was 81.3 cmH2O/sec/min (±30.8) and 64.4 cmH2O/sec/min (±25.3) at baseline and 40 l/m respectively (P=.044). ConclusionsThe use of high-flow oxygen therapy through nasal cannula of HFNC in healthy subjects decreases the DTf and RR in association with increased flow. In addition, the use of 40 l/m flow may reduce the muscular work associated with respiration.