Fourth, we studied only 40 mixed medical and surgical
subjects, and only subjects with mild to moderate respiratory
failure, so we cannot extrapolate our findings directly
to other types of patients. With more subjects and more types of subjects, multivariate analysis might have revealed HFNC benefits in specific types of patients. Finally, we were unable to elucidate the mechanisms by which HFNC improved thoraco-abdominal synchrony. Measurements of oropharyngeal airway pressure and transpulmonary pressure
(derived from esophageal pressure) might help clarify this question.