Test of Chamber Pressure to Divers and Chamber Attendants

Not Applicable

Completed

Interventions: Drug: Sham Chamber Session
Drug: Hyperbaric Oxygen (1.5 atm abs)

Brief Summary: SCUBA divers and chamber inside attendants will undergo a brief hyperbaric chamber excursion and will be asked to what chamber pressure they were compressed and what gas they breathed.

Detailed Description: 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.

Recruitment & Eligibility

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

Arm && Interventions

Group	Intervention	Description
Sea Level Equivalent 1.2 atm abs (air)	Sham Chamber Session	Sham Chamber Session Sea Level Equivalent 1.2 atm abs (2.6 psig) breathing regular air 20-chamber excursion
Altitude Equivalent 1.2 atm abs (air)	Sham Chamber Session	Sham Chamber Session Altitude Equivalent 1.2 atm abs (5.1 psig) breathing regular air 20-minute chamber excursion
Sea Level Equivalent 1.5 atm abs (O2)	Hyperbaric Oxygen (1.5 atm abs)	Hyperbaric Oxygen (1.5 atm abs) Sea Level Equivalent 1.5 atm abs (6.2 psig) breathing 100% oxygen 20-minute chamber excursion
Altitude Equivalent 1.5 atm abs (O2)	Hyperbaric Oxygen (1.5 atm abs)	Hyperbaric Oxygen (1.5 atm abs) Altitude Equivalent 1.5 atm abs (9.6 psig) breathing 100% oxygen 20-minute chamber excursion

Primary Outcome Measures

Name	Time	Method
Participants Indicating "I do Not Know" on Depth Questionnaire.	Within 15 minutes of chamber excursion	Participants indicating "I do not know" on depth questionnaire instead of providing a free response guess.
Participant Perception of Depth	Within 15 minutes of chamber excursion	Mean depth perception for participants providing a free response.
Participant Perception of Breathing Gas	Within 15 minutes of chamber excursion	Percent of participants in each arm guessing that their breathing gas was 100% oxygen.