Conclusion
Our study assessed FO2 insp. and FO2pre-insp. during nasal cannula oxygen therapy in a spontaneous breathing lung model and suggested that multiple factors influence the measured FO2 insp. and FO2 pre-insp. under low-flow nasal cannula, such as respiratory patterns, additional VT, f and inspiratory or expiratory time, which indicate the short-term storage of oxygen in an anatomic space between the end-expiratory period and the next inspiratory period, as in the normal, restrictive and obstructive lung models. As such, an increased VT cause a decrease in FO2 insp. and FO2 pre-insp. measured in the carina. As VT and f decrease, there is less difference between FO2 pre-insp. and FO2 insp.; therefore, any variation in the total expiratory time will affect the oxygen reservoir in the next inspiration. The results of this bench study provide a reference for clinicians and researchers regarding various lung mechanics and respiratory patterns under low flow nasal cannula.