Pulmonary Function Following Hyperbaric Oxygen Therapy: A Prospective Cohort Study
Conditions: Oxygen Toxicity
Sponsor: University of Toronto

Study Protocol and Statistical Analysis Plan 
 
 
 
 
 
 
 
 
Pulmonary Function After Hyperbaric Oxygen Therapy 
NCT05088772 
2023-Jul-09 
 

Study Protocol and Statistical Analysis Plan 
Study design and participants 
 
We conducted a retrospective analysis of prospectively collected data on a cohort of  
patients undergoing HBOT at the University Health Network’s Hyperbaric Medicine Unit in 
Toronto, ON, Canada, between February 2016 and June 2021. All studied patients provided 
written consent to undergo HBOT (for a variety of clinical indications), and were scheduled to 
receive at least ten cycles of treatment at our large referral center during this timeframe. Patients 
underwent PFT assessment before starting HBOT and following every 20 treatment sessions 
thereafter. 
  
Research ethics approval for the analysis of these data was provided by the University 
Health Network (Toronto, ON) Research Ethics Board (CAPCR ID: 19-5081.1). Data were 
collected retrospectively from the electronic records of enrolled patients, and comprised 
demographic information, HBOT indication and protocol, treatment complications, and PFT 
results immediately before the first HBOT session and following every subsequent 20 
treatments. The protocol was retrospectively registered during the data collection stage and prior 
to analysis on Clinicaltrials.gov (trial ID: NCT05088772). We followed the STROBE guidelines 
for reporting observational cohort studies (S2 Table) [11]. 
 
Hyperbaric oxygen therapy protocol 
The HBOT protocol utilized at our center has been previously described [12]. HBOT was 
performed with 100% O2 at a pressure of 2.4 or 2.0 ATA (243 or 203 kPa) for 90 minutes, with 
1-2 air breaks (0.21 fraction of inspired O2 at the same ATA) per session, five times weekly in 
one of three mono-place chambers (Sechrist 3600H and Sechrist 4100H, Sechrist Industries Inc., 

Study Protocol and Statistical Analysis Plan 
Anaheim, CA, USA; PAH-S1-3200, Pan-America Hyperbarics Inc., Plano, TX, USA) or through 
a plastic hood in a multi-place chamber (rectangular Hyperbaric System, Fink Engineering PTY-
LTD, Warana, Australia). 
 
Pulmonary function testing protocol 
Bedside spirometry was performed by a trained respiratory therapist using a KoKo Trek 
USB Spirometer software and pneumotachometer (KoKo, USA). Pulmonary function tests were 
completed at the time of consultation (prior to the first HBOT treatment) and following every 20 
treatments thereafter. In rare cases when PFTs could not be obtained on the exact date of a 20th, 
40th, or 60th treatment (e.g., due to equipment limitations), they were obtained on the nearest 
possible date of another treatment and rounded to an increment of 20 at the time of data analysis. 
The spirometry equipment was calibrated at the beginning of each day. Patients were tested in a 
seated position with nose clips, in accordance with American Thoracic Society testing criteria 
[13], and results were compared against Knudson reference values [14] to determine their 
percentage of predicted values based on age, sex, and height. To capture potential restrictive, 
obstructive, and effort-independent changes, three markers of dynamic lung function were 
recorded: FEV1% (percentage of predicted FEV1), FVC% (percentage of predicted FVC), and 
FEF25-75% (percentage of predicted FEF25-75). The data utilized in this study comprise the highest 
readings for each of these variables from three satisfactory forced expiratory maneuvers 
performed as part of each PFT assessment. The primary outcome of this study was change in 
spirometry performance over the course of HBOT. We additionally classified the degree of any 
baseline PFT abnormalities on the basis of each independent parameter’s deviation from the 

Study Protocol and Statistical Analysis Plan 
predicted value, designating mild abnormality as 70-79%, moderate abnormality as 60-69%, and 
severe abnormality as less than 60%. 
 
 Data collection and statistical analysis 
Patient demographic data and past medical history characteristics were summarized using 
descriptive statistics, and continuous data were expressed as means ± standard deviations. Linear 
mixed effect regression models were used to estimate the adjusted sample mean scores of PFT 
outcomes FEV1%, FVC%, and FEF25-75% at each timepoint for the cohort. Timepoint was 
included as the fixed effect and individual subject as the random effect for each outcome for the 
overall cohort. PFT outcomes were also modeled for subgroups by timepoint interaction for pre-
existing respiratory disease, smoking status, and treatment pressure (in ATA). Similarly, 
individual subjects were included as random effects. The maximum likelihood estimation was 
used to prepare the mixed models and analyzed under the intention-to-treat principal. Post-hoc 
pairwise comparisons between timepoints were conducted for each grouping of pre-existing 
respiratory disease, smoking status, and treatment pressure, for each PFT variable. Pairwise 
comparisons were adjusted using Tukey’s HSD. The alpha was set to 0.05. All analyses were 
performed using R version 4.0.3. 
 
Objectives 
 
The primary objective of this study was to evaluate changes in series of pulmonary 
function tests (PFTs) performed over the course of recurrent HBOT exposures. A secondary 
study outcome was the incidence of pulmonary complications such as lung barotrauma.