A blinded trial to investigate whether 'pressure-familiar' individuals can determine chamber pressure.
BACKGROUND
We conducted a prospective study to determine whether divers or hyperbaric chamber attendants could discern chamber pressure--important to protecting blinding if they were to participate in blinded hyperbaric oxygen (HBO2) trials.


METHODS
Experienced divers and chamber attendants were randomized by appointment group to one of four pressure changes. These pressure changes caused volume changes corresponding to starting compression from sea level or altitude, with final pressures of 1.5 atm abs (breathing 100% oxygen) or 1.2 atm abs (breathing air). Following the pressure excursions, participants estimated their depth in feet of sea water (fsw) and breathing gas.


RESULTS
42 volunteers participated: 10 females, 32 males, age 46 +/- 10 years (mean +/- 1 SD), dive experience 366 +/- 562 dives. Four were chamber attendants. When estimating the depth exposure, 19/42 (45%) selected I do not know. 3/23 (13%) were within 2 fsw of the actual depth (correlation between actual depth and estimate -0.0067) (p = 0.98). Two underestimated their depth. We found no indication of cluster randomization effect (p = 0.16). Participants could not discern breathing air or oxygen.


CONCLUSIONS
The results suggest experienced divers cannot discriminate chamber pressures of 1.2 and 1.5 atm abs, and could be included in hyperbaric clinical trials using this dosing without compromising masking integrity.
Hyperbaric Medicine, Intermountain LDS Hospital, Salt Lake City, Utah, USA. lindell.weaver@imail.org
Lindell K
LK
Weaver
Susan K
SK
Churchill
James
J
Bell
Kayla
K
Deru
Gregory L
GL
Snow
D000328:Adult; D000388:Air; D000488:Allied Health Personnel; D001273:Atmosphere Exposure Chambers; D001274:Atmospheric Pressure; D004242:Diving / Q000502:physiology*; D005260:Female; D006801:Humans; D006931:Hyperbaric Oxygenation / Q000379:methods*; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000008:administration & dosage; D010465:Perception / Q000502:physiology*; D011446:Prospective Studies; D012677:Sensation / Q000502:physiology; D055815:Young Adult
D010100:Oxygen