Respirator and Breathing Compartments

The study involved 21 students majoring in physical education and sports. All subjects were physically active, engaging in approximately 260 minutes of physical activity per week, and they possessed a high level of fitness. Inclusion criteria required participants to be free from injury, capable of providing written consent, and within the age range of 19 to 26 years. Exclusion criteria included individuals who smoked or had chronic pulmonary or cardiac diseases. This research received approval from the Ethics Committee at the Faculty of Education, University of South Bohemia, Reference Number: 002/2018. All procedures conducted within the study adhered to the ethical standards outlined by the Institutional Research Committee and the principles of the Helsinki Declaration.

Protocol:

Participants were instructed to visit the laboratory on two occasions to complete two separate tests during each session, specifically the Opto-electronic plethysmography (OEP) test during resting in a standing position and the OEP test during a Graded Exercise Test (GXT). The time interval between the testing days was three days. Participants were randomly assigned to two groups using randomizer.org. The first group performed three tests while wearing a Face-Fit Respirator (FFR), while the second group performed the tests without the mask. During the second visit, participants switched to the opposite condition. The N95 respirator was employed in this study as the gold standard for protection against aerosol transmission, particularly during the COVID-19 pandemic. A new mask was used for each test. In the Standing Test (STD), participants were instructed to maintain a stationary standing position and engage in spontaneous, quiet breathing without speaking or altering their posture while OEP data was collected. The first two minutes were designated as an adaptation period, followed by data collection for an additional three minutes. In the context of the Graded Exercise Test (GXT), OEP data was collected during the final minute of each three-minute stage.

Opto-Electronic Plethysmography:

The analysis of breathing patterns and volumes of chest wall compartments was conducted using opto-electronic plethysmography (BTS Bioengineering, Milan, Italy). This device comprises eight cameras, with five positioned anteriorly and three posteriorly relative to the participant. Additionally, 89 reflective markers were affixed to the participant's chest, abdomen, and back to track movements of the trunk. This technique has previously demonstrated validity in both resting and maximal exercise conditions.

The contributions of each breathing compartment (VRCp - pulmonary rib cage, VRCa - abdominal rib cage, VAb - abdomen) were determined by calculating the difference between end-inspiratory and end-expiratory volumes. The specific methodology for calculating chest wall kinematics using OEP has been detailed in prior research.

Graded Exercise Tests:

To complete this study, participants were required to undergo two maximal graded exercise tests (GXT) on separate days, one with the use of a Face-Fit Respirator (FFR) and one without. After three minutes of warm-up walking (2.7 km/h, 10% incline), participants performed the Bruce Protocol until exhaustion. The Bruce Protocol was conducted on a treadmill (Lode Valiant 2 Sport, Lode B.V., Groningen, Netherlands). All tests were conducted at the same time of day to mitigate the influence of circadian rhythms. Immediately following the completion of the test, participants provided ratings on the Modified Borg Dyspnea Scale, which ranges from 0 to 10, to assess breathlessness.

Inclusion criteria

• physically active (~260 min/week) possessing high fitness level,
• free from injury,
• able to give full written consent,
• meet age criteria 19-26 years.

Exclusion criteria

• smokers,
• chronic pulmonary disease,
• cardiac disease.