Study design and population
This was a single-center prospective observational study approved by the Institutional Research Ethics Board. Signed informed consent was obtained from all participants. The study population comprised physicians, nurses, and medical trainees working at the Sheba Medical Center ED between September and November 2020 who were assessed during 4-hour shifts while continuously wearing an N95 respirator. Subjects with any health condition that could potentially put them at risk, such as chronic obstructive pulmonary disease, uncontrolled asthma, pulmonary hypertension, or poorly controlled heart failure, were excluded. Baseline demographic data were collected, including age, gender, medical history, and previous or active cigarette smoking.