Hypoxic Challenge Test (HCT): Role in flight assessment
Research type
Research Study
Full title
Is the perceived risk of hypoxia during commercial aircraft travel a relevant risk for individuals who are respiratory compromised, and are we assessing appropriately or are there more effective methods to ensure normoxia?
IRAS ID
251944
Contact name
Ian Cliff
Contact email
Sponsor organisation
University Hospitals of North Midlands
Duration of Study in the UK
0 years, 11 months, 31 days
Research summary
Research Summary: The reduced pressure in a commercial aircraft cabin may cause significant hypoxaemia and distress in patients with respiratory disorders. This is due to the airlines pressurising the cabin environment to 8000 ft. which reduced the fractional inspired oxygen (FiO2) from 21% (sea level) to 15.1%.
The primary aim of the research is to investigate to what extent in-flight hypoxia effects patient symptoms and if exposure is detrimental (commercial flight experience questionnaire). Furthermore, it will be proposing alternative methods of performing hypoxic challenge test (HCT) that are in keeping with in-flight oxygen delivery by commercial airlines. Furthermore, other physiological measures will be assessment to investigate the ability to predict individuals who are at risk of developing significant hypoxia during flight.
The groups under investigation include chronic obstructive pulmonary disease, interstitial lung disease and muscle-skeletal disorders. These patients will be selected from general respiratory clinic, interstitial lung disease service and ventilation clinics, with the latter providing access to motor neurone disease and extrathoacic deformed patients.
The study will be conducted at the Royal Stoke University Hospital.
The study will last for 12 months starting at the April 2019 and closing April 2020. The participant will complete a 2 part questionnaire the baseline questionnaire relates to their previous flight experience and follow-up questionnaire is to be completed post flight . They will also perform a HCT which simulates the commercial flight cabin environment (FiO2 15%) and the corrective management (supplemental oxygen) required to maintain normoxyia by means of continuous and pulsed oxygen therapy. Further investigations include overnight oximetry, pulmonary function tests, activity of daily living questionnaire and field exercise tests.
Summary of Results: Assessing Fitness to Fly in Respiratory Patients
This research investigates whether existing clinical data and historical assumptions—primarily based on patients with Chronic Obstructive Pulmonary Disease (COPD)—can be used to assess the fitness to fly of patients with other respiratory conditions, specifically Motor Neurone Disease (MND) and Interstitial Lung Disease (ILD).
Background
Air travel exposes passengers to lower oxygen levels due to cabin pressure equivalent to 8,000 feet altitude. While healthy individuals tolerate this well, those with respiratory conditions may experience hypoxaemia (low blood oxygen), which can lead to serious complications. The British Thoracic Society (BTS) has guidelines for assessing fitness to fly, but these are largely based on COPD data.
Study Aim
The study aimed to:
Compare physiological responses to simulated flight conditions (via Hypoxic Challenge Tests or HCTs) among patients with COPD, MND, and ILD.
Evaluate whether routine clinical data (such as spirometry and blood gases) can predict the need for in-flight oxygen.Methods
Retrospective analysis of 225 patients (118 MND, 56 ILD, 51 COPD) who underwent HCTs between 2010 and 2020.
Data included lung function tests, blood gas measurements, and other clinical parameters.
Statistical models were used to identify predictors of HCT outcomes.Key Findings
COPD patients had the highest failure rate in HCTs, indicating a greater need for in-flight oxygen.
MND patients showed significant differences in spirometry and blood gases between those who passed and failed HCTs, but muscle strength (SNIP) was not a reliable predictor.
ILD patients had less predictable outcomes; standard lung function tests and transfer factor measures did not reliably indicate who would fail the HCT.
Across all groups, routine clinical data had limited predictive power for identifying patients at risk of hypoxaemia during flight.Conclusions
Historical assumptions based on COPD cannot be reliably applied to MND or ILD patients.
The Hypoxic Challenge Test remains the most accurate method for assessing fitness to fly.
Routine tests like spirometry and blood gases are not sufficient to predict in-flight oxygen needs.
Each patient should be assessed individually, and disease-specific guidelines are needed.Implications
This study highlights the need for updated clinical guidelines that reflect the unique risks faced by different respiratory patient groups during air travel. It also calls for further research into predictive tools and assessment methods, including the role of oxygen delivery modalities (continuous vs. pulsed) and the use of portable oxygen concentrators
Has the registry been updated to include summary results?: No
If yes - please enter the URL to summary results:
If no – why not?: This study aimed to explore whether current methods used to assess the risk of low oxygen levels (hypoxia) during commercial air travel are suitable for people with respiratory conditions. It also investigated whether alternative approaches, such as the Hypoxic Challenge Test (HCT), could offer more accurate assessments to ensure passengers remain safely oxygenated during flights.The study began in August 2019 and was planned to recruit 120 participants. However, due to the COVID-19 pandemic, recruitment was severely impacted. Travel restrictions and increased clinical demands led to a significant reduction in referrals to the respiratory physiology service. As a result, only 8 participants completed the study.
Despite the limited sample size, no safety concerns or adverse events were reported. The study was registered on ClinicalTrials.gov (NCT04272268) and remains open, with a revised expected completion date of July 2025.
Due to the small number of participants, the study did not generate sufficient data to draw firm conclusions about the effectiveness of current assessment methods or the potential benefits of HCT. Nonetheless, the findings contributed to ongoing discussions in the field and were presented at the British Thoracic Society Winter Meeting 2023.
REC name
South Central - Oxford B Research Ethics Committee
REC reference
19/SC/0315
Date of REC Opinion
23 Jul 2019
REC opinion
Further Information Favourable Opinion