To simulate real - world stressors, Paulus had them wear special masks that periodically restricted their air intake for a few seconds, making them tense up and gasp. (discovermagazine.com)
Using pressurization, it could allow lung disease patients and deep - sea divers to draw oxygen directly from their environment using special masks. (discovermagazine.com)
If that does nt do the trick, special masks containing heat exchangers can be helpful. (health.com)