Study design and participant enrollment
The study wasa prospective observational study.Volunteers were recruited from [removed for blind peer review] between October and November 2019. It was approved by the institutional review board of the hospital (201910015RINC) and registered at ClinicalTrials.gov (NCT04175483).
The enrollment document was publicly available on bulletin boards for 1 month before the recruitment. Healthy volunteers aged more than 20 years were included in this study. Exclusion criteria included preexisting airway obstruction, or respiratory diseases such as asthma and chronic obstructive pulmonary disease, neck tumors, and a history of neck operation or smoking. An independent investigator, who was not involved in measurement and data analysis, recruited volunteers.Written informed consent wasobtained from each participant.