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.