An observational study in Hypoxia, sponsored by Mayo Clinic. Active, not recruiting at 2 sites in United States. Open to participants aged 18 Years to 65 Years, including healthy volunteers. Per ClinicalTrials.gov, last updated 2026-01-30.
Sponsored by Mayo Clinic · Observational
The purpose of this study is to develop a single, standardized test to determine how individuals tolerate acute hypoxia in a stepwise fashion. We aim to evaluate the association between multiple factors, such as ventilatory compensation, heart rate response, acid-base changes, sex, pulmonary function, etc, which may explain why some individuals tolerate exercise in hypoxia better than others. Identifying these factors of association will inform future pharmacological and non-pharmacological attempts to combat acute hypoxic exercise.
1,231 studies on the registry are indexed under Hypoxia; 241 are open to participants now.
This study's planned enrollment of 50 is below the median of 67 across 335 observational studies indexed under Hypoxia.
Browse Hypoxia studies →Mayo Clinic is the lead sponsor of 3,218 studies on the registry; 670 are open to participants now.
Of its 445 completed or terminated interventional studies of FDA-regulated products, 313 (70%) have results posted.
Counted across the registry records on this site, refreshed daily.
A total of 50 participants (25 female, 25 male) will be recruited for this study. Participants will be recruited from the general population.
Exclusion Criteria:
50 participants (25 female, 25 male) who are physically active for at least 150 minutes per week, at a moderate activity level.
Diagnostic Test: Graded Exercise Test · Diagnostic Test: Graded Hypoxia Exercise Test
Participants will perform a graded exercise test on either a cycle ergometer or treadmill. The testing protocol will begin with a 5- 10 min warm-up of either cycling or running/walking at the participants preferred pace. If the graded exercise test is on a bike, exercise will begin at wattage that elicits \~50% of their heart rate max, HRmax = 208 - 0.7 × age and increase by either 10W, 15W, or 20W every two minutes in a stepwise fashion until symptom limitation. The step of the wattage increase will be at the discretion of the investigators. If the graded exercise test is on a treadmill, the test will begin at a speed that elicits \~50% of predicted HRmax. Following, the speed of the treadmill will increase 0.5 mph (0.8 km/hr) every two minutes in a stepwise fashion until symptom limitation. If the participant maxes out the speed of the treadmill, we will increase the grade 2% every 2-minutes until symptom limitation.
Participants will perform a single constant work rate exercise tests during graded hypoxia. They will be outfitted with either a facemask or mouthpiece connected to a uni-directional breathing valve. During inspiration, subjects will breathe from a closed-system Douglas bag balloon reservoir (\~200 L) connected to the value on the inspired side via air-tight clean-bor tubing. The participant will complete the same mode of exercise as they did during visit 1, either bike or treadmill. The resistance on the bike or incline of the treadmill will be set to elicit an intensity equivalent to \~50% of their V̇O2max determined during visit 1. Participants will complete 5-minute stages over a range of FiO2 values. The exercise test will begin in an FiO2=0.21 (i.e. room air). Following this first 5-min stage the FiO2 will increase to 0.25, afterwards, participants will complete another stage at FiO2=0.21 and then decrease in a stepwise fashion every 5-minutes.
PaO₂/FiO₂ Ratio
The PaO₂/FiO₂ ratio is a widely used measure of oxygenation efficiency in the lungs. It compares the arterial oxygen partial pressure (PaO₂, measured in mmHg) to the fraction of inspired oxygen (FiO₂, expressed as a decimal). The ratio provides insight into the ability of the lungs to transfer oxygen into the bloodstream. A PaO₂/FiO₂ ratio of 300-400 is considered to be mild hypoxemia. Participants are considered as poorly tolerating hypoxia if their ratio is \<400 and good at tolerating hypoxia if their ratio is \>400.
Time frame: 30 minutes
Plan to share: No
No publications or documents are linked to this record.
This study is active, not recruiting, as verified in Jan 2026. You cannot join it, but the record below documents what was studied.
Get an email when the registry record changes — status, dates, results — or when someone posts here.
Sign in to followQuestions and observations about this study, from anyone following it. Not medical advice, and not a channel to the study team — their contact details are on the registry record.
Sign in to join the discussion. Reading takes no account; posting does. You choose a display name, and a pseudonym is the default.
Nothing here yet. If you are running this trial, taking part in it, or weighing whether to, this is the place to say so.
Mayo Clinic