Study design
CM
BLOOD, LEAKAGE
Each subject was tested with four different mask situations (surgical mask (SM), community cloth mask (CM), a filtering face piece (FFP2) and without wearing a mask (NM) as reference) in a randomized order. The cross-over study design was based on four different modules performed also in a randomized order to investigate different physiological parameters that may be influenced when wearing a face mask: body plethysmography (1) and CPET (2) were performed to study breathing physiology and cardiopulmonary parameters at rest and during exercise under standardized conditions without leakage of the mask. In these two modules the mask material was presented to subjects in a double-blinded setting using a mask adapter (Fig. Mask adapter. (In module 1, the washout periods between each mask situations lasted at least 30 min. If the subjects were not ready for a subsequent intervention, they were given an additional 30 min resting time. In modules 2–3, the washout periods between each exercise test lasted at least 5 h. Blood gas samples was drawn to control if subjects had regained a physiological resting state. For module 4, the washout period between each mask situations was more than 48 h. In all four modules, each session was performed at a comparable time of the day with comparable routines (i.e. working days).