Methods
All participants involved in this study gave their informed consent. The institutional review board of our hospital approved the study (No.KYLL-202210-24, November 2022). In total, 35 healthy adults (16 men, 19 women) aged 18 to 40 years were enrolled in this study, and all were university students. General demographic data were collected from all volunteers, including sex, age, height, weight, and body mass index (BMI). Individuals who had a history of upper respiratory infection in the past 2 weeks, had a history of smoking, or used drugs influencing cardiopulmonary function were excluded. Three different sizes (3, 4 and 5 mm) of nasal cannulas (Excellentcare Medical Ltd., Huizhou, Guangdong Province, China), which were typical of the most commonly used sizes in our hospital, and two different HFNC devices [HFT-300 (Weishengkang Medical Technology Co, Ltd., Jiangsu China) and H-80 M (BMC Medical Co, Ltd., Beijing China)] were used in the study.