Human Adaptations to Multiday Saturation on NASA NEEMO
Extreme environments have been explored for over a century to understand human adaptation, extrapolate insights into comparative pathology, and extend human exploration (Tipton, 2016). These include spaceflight/microgravity, high altitude/hypobaric, undersea/hyperbaric, cold/hypothermic, and hot/hyperthermic environments. These environments provide individual or multiple external stimuli and stressors which are sufficient to disrupt internal homeostasis and induce adaptation processes (Taylor and Cotter, 2006; Tipton, 2016). From this list of unique terrestrial and extraterrestrial extreme environments, undersea/hyperbaric is unique… It is arguably the least understood, potentially most dangerous, and thus far, the most notoriously difficult to understand due to inherent logistical and safety concerns with evaluating humans in this aqueous, unbreathable medium. There remain very few published studies in this real-world environment.
In an effort to undercover what happens to the human body when pushed to extremes in some of the most demanding and understudied environments on earth, our multi-institution and interdisciplinary team studied the multisystem human adaptations that occur when humans live 60ft underwater for 9-10 days straight on National Aeronautics and Space Administration (NASA) Extreme Environment Mission Operations (NASA NEEMO).
The unique nature of this environment and these findings are summarized below:
World’s Only Operationally Relevant Hyperbaric Environment
Aquarius Undersea Research Laboratory (AURL) is the world’s only existing underwater hyperbaric/saturation research laboratory (9km offshore & 19.2 meters sea depth), allowing highly trained operators to live and operate multiple days underwater (ecological) in >2.34 ATA of pressurized gas. Consequently, AURL provides the only real-world hyperbaric saturation environment for elucidating human adaptation to >24hour hyperbaric saturation.
Photo credit FIU Aquarius reef base
Check out the Aquarius habitat on Google Earth satellite images
Exclusive Operational Population
Aquanauts illustrate one of the world’s most unique operational population. To date, only <200 people have ever lived in AURL >24hours. Our evaluation encompassed 11 NASA-selected participants: 4 astronauts, 4 researchers, and 3 habitat technicians.
NASA NEEMO
NEEMO is a space flight analogue mission conducted by NASA with hand-selected operators requiring a year of planning across multiple institutes, replicating mission task load and demands, communication logistics, geographical isolation, extravehicular activities (EVAs), and associated risks. We conducted research evaluation across two back-to-back NEEMO missions, the only research study to do so.
Multiday Multi-day Saturation
Hyperbaric saturated stressors are the most difficult to evaluate due to inherent limitations (experimental, analytical, technical, temporal, and safety), with almost a complete absence of published PubMed indexed research evaluating chronic hyperbaric saturation (>24 hours). We effectively elucidated the response to and recovery from multiday saturation (9-10 days) across multiple timepoints.
Multi-component Evaluation
We conducted a multi-component evaluation across intrapersonal burden, mood and work satisfaction, cardiac, respiratory, autonomic, thermic, peripheral and cerebral hemodynamics, objective and subjective sleep, and body composition parameters using advanced technologies. No published research study to date has done such a comprehensive analysis.
Multi-system Adaptations
We found that aquanauts exposed 9–10d saturation experienced intrapersonal burden, sustained good mood & work satisfaction, decreased heart & respiratory rates, increased parasympathetic & reduced sympathetic modulation, lower cerebral blood flow velocity, intact cerebral autoregulation and maintenance of baroreflex functionality, as well as losses in systemic body weight and adipose tissue.
We had many predictions on what the body would do to adapt to this unique environment… but many of our hypotheses were flat out wrong. While we never knew what to expect when going into this experience, it really illustrated one of the most gratifying scientific endeavors. It also happened to result in some really cool findings. We hope this work will help advance our understanding of human adaptation to some of the most extreme stressors the earth can provide, extrapolate insights into comparative pathology, and extend human exploration.
