Test of Chamber Pressure to Divers and Chamber Attendants

In clinical trials evaluating hyperbaric oxygen, blinding can be challenging. Options for participant blinding include offering regular air at a lower pressure than the hyperbaric oxygen intervention, or compressing all participants to the same pressure but providing different gas mixes to the active and sham arms.

In some trials of hyperbaric oxygen for brain injury, investigators offer a sham chamber session (regular air at 1.2 atmospheres absolute [atm abs]) compared to the active intervention, hyperbaric oxygen (100% oxygen at 1.5 atm abs). It is unknown whether individuals familiar with pressure changes, such as divers and hyperbaric chamber inside attendants, could discern the difference between these pressures and thereby become unblinded to study allocation.

In this study, 80 experienced divers and chamber inside attendants will be enrolled and randomly assigned to one of four possible chamber pressures and one of two breathing gases. After a brief hyperbaric chamber excursion, they will be asked to what chamber pressure they were compressed and what gas they breathed. If participants can accurately report chamber pressure or breathing gas, pressure-familiar individuals should be excluded from blinded clinical trials of hyperbaric oxygen.

Inclusion criteria

• Adult, age 18 - 65 years
• Completion of medical history questionnaire without concerns identified for exposure to increased pressure
• Familiarity with atmospheric pressure change:
• Experienced and active hyperbaric chamber inside attendant: more than 50 hyperbaric compressions, with more than 4 have been in the last 4 months; or
• Experienced and active SCUBA diver: more than 20 lifetime compressed gas open water (not swimming pool) dives, with more than 10 in the last 12 months
• Able to equalize middle ear pressure easily

Exclusion criteria

• Pregnancy
• Known risk for barotrauma, as identified on the medical history questionnaire, such as:
• Recent (within 12 months) inner ear or sinus surgery
• Spontaneous pneumothorax
• Pulmonary cysts
• Emphysema
• Bullous lung disease
• Chronic obstructive pulmonary disease needing chronic active therapy
• Inability to tolerate chamber confinement or pressure
• Presence of heart failure
• Presence of any implanted electrical device, except hyperbaric-approved pacemakers
• Presence of middle-ear tympanostomy tubes