Figure 1.

Setups evaluated in the experiments. (1) Mask, filter, and right-angle connector in which a 4-mm hole has been made (courtesy of C. R.); (2) mask, filter, and a whisper swivel exhalation valve; (3) mask, T-connector, filter, and whisper swivel exhalation valve; (4) mask, 3D-printed piece with a 4-mm leak (provided courtesy of M. P., E. F., and J. G.-B., and shown in more detail in e-Fig 2; see KerNel Biomedical¹² for availability), and bacterial filter; (5) mask, dual-limb circuit with filter on the inspiratory and expiratory circuits; (6) mask, active expiratory valve, and bacterial filter; (7) mask, filter, and active expiratory valve; (8) helmet interface, bacterial filter on the inspiratory and expiratory circuits; (9) Boussignac CPAP montage, bacterial filter between valve and mask.