> Each treatment included 20‐minute pure oxygen inhalation (O2 = 99.9%, oxygen supply pressure 0.4 to 0.7 MPa, oxygen flow 10 to 15 L/h), 15 minutes interval, and then another 20‐minute pure oxygen inhalation (O2 = 99.9%, oxygen supply pressure 0.4 to 0.7 MPa, oxygen flow 10 to 15 L/h) under the pressure of 0.22 MPa (0.12 MPa on pressure gauge) in hyperbaric oxygen chamber (Medical Oxygen Chamber, SY3200‐8500, Yantai Hongyuan Oxygen Industrial Inc., Shandong, China).
Controls that spring to mind would be to have the chamber pressurised to a lower pressure (if you're not already familiar with hyperbaric chambers, you won't know it's at a lower pressure), or to replace the pure oxygen with normal air. Showing a dose-response relationship to pressure or oxygen concentration would go a long way towards making up for the lack of a true negative control.
Controls that spring to mind would be to have the chamber pressurised to a lower pressure (if you're not already familiar with hyperbaric chambers, you won't know it's at a lower pressure), or to replace the pure oxygen with normal air. Showing a dose-response relationship to pressure or oxygen concentration would go a long way towards making up for the lack of a true negative control.