TY - JOUR
AU - Deaton,, Travis
AB - Abstract Introduction Physiological events (PEs) are a growing problem for US military aviation with detrimental risks to safety and mission readiness. Seeking causative factors is, therefore, of high importance. There is no evidence to date associating carbon dioxide (CO2) pre-flight exposure and decompression sickness (DCS) in aviators. Materials and Methods This study is a case series of six aviators with PE after being exposed to a rapid decompression event (RDE) with symptoms consistent with type II DCS. The analysis includes retrospective review of flight and environmental data to further assess a possible link between CO2 levels and altitude physiologic events (PEs). IRB approval was obtained for this study. Results This case series presents six aviators with PE after being exposed to a rapid decompression event (RDE) with symptoms consistent with type II DCS. Another three aviators were also exposed to a RDE, but remained asymptomatic. All events involved tactical jet aircraft flying at an average of 35,600’ Mean Sea Level (MSL) when a RDE occurred, Retrospective reviews led to the discovery that the affected individuals were exposed, pre-flight, to poor indoor air quality demonstrated by elevated levels of measured CO2. Conclusion PEs are a growing safety concern for the aviation community in the military. As such, increasing measures are taken to ensure safety of flight and completion of the mission. To date, there is no correlation of CO2 exposure and altitude DCS. While elevated CO2 levels cannot be conclusively implicated as causative, this case series suggests a potential role of CO2 in altitude DCS through CO2 direct involvement with emboli gas composition, as well as pro-inflammatory cascade. Aviators exposed to elevated CO2 in poorly ventilated rooms developed PE symptoms consistent with DCS, while at the same command, aviators that were exposed to a well ventilated room did not. This report is far from an answer, but does demonstrate an interesting case series that draws some questions about CO2’s role in these aviator’s DCS experience. Other explanations are plausible, including the accurate diagnosis of DCS, health variables amongst the aviators, and differences in aircraft and On-Board Oxygen Generation Systems (OBOGS). For a better understanding, the role of environmental CO2 and pre-flight exposure as a risk of DCS should be reviewed. Physiologic event, Decompression sickness, decompression illness, carbon dioxide, aviation medicine INTRODUCTION Aviators are potentially exposed to a host of unique physiologic stresses such as acceleration forces, temperature extremes, toxic gases, barometric pressure changes and hypoxic breathing environments. Given the complex interface between human-machine relationships, the ability to effectively operate high performance jet aircraft remains a priority for aircrew safety and mission completion. In 2016, Naval Aviation reported a record number of unanticipated symptoms that were distracting to the safe operation of the aircraft or degraded the mission.1 In order to capture these events for reporting and to standardize medical testing and treatment, a Clinical Practice Guideline was developed with a generalized diagnosis of Physiological Events (PEs)1 (Table I). TABLE I. List of Potential Physiological Event Symptoms.1 Feeling slowed or “off” Vertigo or “room-spinning” sensation Memory difficulties Headache Feeling euphoric or elated Fatigue or drowsiness Dizziness Personality changes Disorientation Nausea Anxiousness / Nervousness Changes in thought processes Skin rashes Difficulty breathing Any other symptoms of DCS I / II Pain anywhere, esp. in joints Light-headedness Vision changes or complaints Difficulty communicating Clumsiness Feeling slowed or “off” Vertigo or “room-spinning” sensation Memory difficulties Headache Feeling euphoric or elated Fatigue or drowsiness Dizziness Personality changes Disorientation Nausea Anxiousness / Nervousness Changes in thought processes Skin rashes Difficulty breathing Any other symptoms of DCS I / II Pain anywhere, esp. in joints Light-headedness Vision changes or complaints Difficulty communicating Clumsiness TABLE I. List of Potential Physiological Event Symptoms.1 Feeling slowed or “off” Vertigo or “room-spinning” sensation Memory difficulties Headache Feeling euphoric or elated Fatigue or drowsiness Dizziness Personality changes Disorientation Nausea Anxiousness / Nervousness Changes in thought processes Skin rashes Difficulty breathing Any other symptoms of DCS I / II Pain anywhere, esp. in joints Light-headedness Vision changes or complaints Difficulty communicating Clumsiness Feeling slowed or “off” Vertigo or “room-spinning” sensation Memory difficulties Headache Feeling euphoric or elated Fatigue or drowsiness Dizziness Personality changes Disorientation Nausea Anxiousness / Nervousness Changes in thought processes Skin rashes Difficulty breathing Any other symptoms of DCS I / II Pain anywhere, esp. in joints Light-headedness Vision changes or complaints Difficulty communicating Clumsiness Physiological event is currently defined by physical impairment of aircrew members causing decreased performance due to a variety of factors.1 Manifestation of symptoms remains purposefully broad and inclusive, and may be self-reported or described by a peer or significant other. The Naval Aviation Enterprise1 is currently hypothesizing two broad categories of causative factors for PE. The first theory contributing to a PE involves changes in aircraft cabin pressurization leading to aviation decompression sickness (DCS). The second theory involves breathing air supply system malfunctions that result in various forms of hypoxia. While these categories specifically address the engineering systems on high performance aircraft, there is a realization that PEs are likely influenced by contributing human factors and physiologic conditions such as fatigue, dehydration, diet, nutrition, anxiety, and hyperventilation.1 Decompression sickness (DCS) related PEs are well described as a potentially debilitating disease affecting divers and aviators. Also known as the “bends”, or caisson disease, DCS is due to nitrogen bubbles escaping formation within the bloodstream, which can cause local tissue irritation, endothelial damage, and platelet aggregation leading to vaso-occlusion.2 In the 1960s, Webb identified bubbles on sonography in study participants exposed to rapid decompression episodes (RDE).3 Webb’s research was able to correlate the area of bubble formation to clinical symptoms such as joint pain, rash, headaches, and paresthesia.3 DCS is classified by organ involvement. Type I, which comprises over 90% of cases, generally includes the skin, limbs, dental, and the lymphatic organ systems. Type II DCS, considered more severe in nature, may involve the inner ear, cardiopulmonary or central nervous systems. If not recognized or appropriately treated post-flight, DCS can lead to long term aircrew disability.3 Of note, carbon dioxide (CO2) is a known asphyxiate with oxygen displacing properties leading to hypoxic injury. Reports have also demonstrated CO2’s neurotoxic properties associated with seizures, headaches, and neurologic deficits.4 There is also evidence to suggest that carbon dioxide is a proinflammatory toxin initiating interleukin and cytokine pathways.5 Due to these factors, it has been proposed that activation of a neuroinflammatory process may lead to DCS like symptoms when exposed to hypobaric conditions.6,7 We present a case series of nine patients who were aviators of high performance jet aircraft involved in RDEs, six of whom developed persistent symptoms concerning for PEs that required treatment with supplemental oxygen or hyperbaric oxygen therapy. All aircrew that required treatment during the time period reported were exposed to elevated levels of carbon dioxide in the pre-flight environment due to a faulty ventilation system in the pre-flight briefing spaces. CASE SERIES Institutional Review Board approval was obtained at Navy Medical Center San Diego department of clinical investigation for this retrospective review. All RDEs discussed occurred at one Naval air base in Nevada. Data collection: Data on aircraft and altitude changes were retrospectively collected from military hazard and physiology reports. Information on non-symptomatic aviators was derived from medical notes and personal discussion with the aviators involved. Data was limited due to the lack of reporting requirements for asymptomatic aviators. Additionally, investigation of the causality was initiated many months after the PEs, making blood analysis and additional CO2 concentration collection unobtainable. Despite this, we were able to collect incidence of RDE and DCS symptoms for nine physiologic events that occurred between June 2014 and November 2015. Subjects: The patients were nine U.S. Naval aviators, ranging in age from 29 to 41 years old. All were in a good state of health, without chronic diseases, considered non-tobacco users, and up to date with their flight physicals. None were involved in a diving event within 48 hours prior to their flight, nor did they express pre-flight symptoms to include headaches, paresthesia, or vertigo. One aviator (#6) later reported being dehydrated prior to the flight, but without symptoms. None of the aviators took medications or supplements on the day of the RDE. Aircraft: All events involved a U.S. Navy tactical aircraft, with six F/A-18C/D/E’s and one F-16. All were up to date with maintenance per standard operating procedure. Two of the aircraft involved a two-seat cockpit, with Aviators 5/6 and aviators 8/9 in F/A-18 D’s. All aircraft landed without event after which all aircrew were seen by the flight surgeon. Pre-flight briefing spaces: Two separate rooms were used for pre-flight briefings. Both rooms were built roughly in the same year, and of the same building materials. They were occupied during regular business hours by squadron, admin, and support personnel. The planning room however, had 4 new HVAC systems due to recent renovation. As the briefing space was a commonality amongst affected aviators, we had concern for poor indoor air quality as a potential causative factor. A metered assessment was performed, and measurements were recorded using a calibrated data-logging indoor air quality meter sampling fluctuations in CO2 as well as Volatile Organic Compounds (VOCs), Relative Humidity (R.H.%) and Temperature (deg F). Continuous sampling was completed in two different rooms used by the aviators. The planning room was used for mission briefs and pre-flight planning. The staging room was used for flight scheduling, weekly mission planning, and socializing. The planning room was measured for eight hours, while the staging room was measured for approximately 24 hours. The results of these measurements included an average R.H. of 5%, and an average temperature of 64.3 deg F. Outdoor CO2 was measured for indoor CO2 comparisons and found to have a mean of 430 ppm. Average indoor CO2 concentration in the planning room was measured at 893 ppm, with a peak of 1,204 ppm (Fig. 1). The average indoor CO2 concentration in change to: the staging room, was measured at 563 ppm, with a peak of 1,040 ppm. Further investigation revealed that the fresh air louvers on the HVAC air handlers within the planning room were locked in the fully closed position. Thus, there was no fresh air being introduced into these pre-flight planning spaces. The staging room was found to have normal functioning ventilation system (Fig. 2). FIGURE 1. View largeDownload slide Indoor air quality (IAQ) results demonstrating carbon dioxide (CO2) and temperature (Temp) from planning room, over time on November 24, 2014. *Approximate average outdoor CO2 concentration. FIGURE 1. View largeDownload slide Indoor air quality (IAQ) results demonstrating carbon dioxide (CO2) and temperature (Temp) from planning room, over time on November 24, 2014. *Approximate average outdoor CO2 concentration. FIGURE 2. View largeDownload slide Indoor air quality (IAQ) results demonstrating carbon dioxide (CO2) and temperature (Temp) from staging room, over time on November 24, 2014 to November 25, 2014. *Approximate average outdoor CO2 concentration. FIGURE 2. View largeDownload slide Indoor air quality (IAQ) results demonstrating carbon dioxide (CO2) and temperature (Temp) from staging room, over time on November 24, 2014 to November 25, 2014. *Approximate average outdoor CO2 concentration. RDE: Seven RDEs occurred at an average altitude of 35,600’ Mean Sea Level (MSL) with a range of 30,000–41,000’ MSL. Each RDE occurred reportedly over a few seconds but there was no objective measurement of time. The average altitude the cabins were pressurized to was 13,400’ MSL and de-compressed to an average of 23,600’ MSL, with an average change of 10,200 feet. All pilots initiated a rapid descent on 100% oxygen (O2), though in most cases the pressurization system recovered before the jet reached 10,000’ MSL. Aircraft maintenance records, and flight conduct were not demonstrated to be causal factors to the RDE. Aviators one through six conducted pre-flight briefing in the planning room, while aviators seven through nine briefed in the staging room (Table II). Briefs were 60 ± 15 minutes, and flight takeoffs occurred on average 1 hour ±30 minutes after conclusion of pre-flight brief. Aviators one through four developed DCS symptoms immediately after the RDE while still in flight and continued post-flight requiring treatment. Aviator one experienced confusion, disorientation, and paresthesia along the right forearm. Aviator two reported slurred speech, cognitive “slowness”, and felt “shaky”. Aviator three felt “lightheaded” and experienced difficulty with concentration. Aviator four had “difficulty concentrating”. These four aviators were treated with HBOT with resolution of symptoms. Aviator one, however, had residual effects and required five days of HBOT. While his confusion ultimately resolved, he continued to have residual paresthesia of the right upper extremity. Aviator five reported lightheadedness which resolved after oxygen supplementation and a meal. Also, aviator six reported headache which resolved after oxygen supplementation and caffeine intake. All six symptomatic aviators returned to flight duty after appropriate observation time following Navy aeromedical guidelines. Aviators seven, eight, and nine were asymptomatic without residual effects. TABLE II. Seven Rapid Decompression Events (RDE) in Seven Tactical Aircrafts That Included Nine Aviators With Comparison of Pre-flight Brief Room, Aircraft (AC), Aviator’s Age, and Symptoms (Sx) RDE Aviator A/C Age Altitude (MSL) Pre-event Cabin Altitude (MSL) Post-event Cabin Altitude (MSL) Sx? Room used for preflight briefing 1 1 F/A-18E 37 40,000 15,000 25,000 ft Yes planning 2 2 F/A-18C 29 31,000 10,000 Unknown Yes planning 3 3 F/A-18C 33 30,000 10,000 Unknown Yes planning 4 4 F/A-18C 30 31,000 10,000 20,000 ft Yes planning 5 5 F/A-18F 30 37,000 12,000 21,000 ft Yes planning 5 6 F/A-18F 40 37,000 12,000 21,000 ft Yes planning 6 7 F-16A 41 41,000 15,000 28,000 ft No staging 7 8 F/A-18 30 37,000 15,000 25,000 ft No staging 7 9 F/A-18 26 37,000 15,000 25,000 ft No staging RDE Aviator A/C Age Altitude (MSL) Pre-event Cabin Altitude (MSL) Post-event Cabin Altitude (MSL) Sx? Room used for preflight briefing 1 1 F/A-18E 37 40,000 15,000 25,000 ft Yes planning 2 2 F/A-18C 29 31,000 10,000 Unknown Yes planning 3 3 F/A-18C 33 30,000 10,000 Unknown Yes planning 4 4 F/A-18C 30 31,000 10,000 20,000 ft Yes planning 5 5 F/A-18F 30 37,000 12,000 21,000 ft Yes planning 5 6 F/A-18F 40 37,000 12,000 21,000 ft Yes planning 6 7 F-16A 41 41,000 15,000 28,000 ft No staging 7 8 F/A-18 30 37,000 15,000 25,000 ft No staging 7 9 F/A-18 26 37,000 15,000 25,000 ft No staging TABLE II. Seven Rapid Decompression Events (RDE) in Seven Tactical Aircrafts That Included Nine Aviators With Comparison of Pre-flight Brief Room, Aircraft (AC), Aviator’s Age, and Symptoms (Sx) RDE Aviator A/C Age Altitude (MSL) Pre-event Cabin Altitude (MSL) Post-event Cabin Altitude (MSL) Sx? Room used for preflight briefing 1 1 F/A-18E 37 40,000 15,000 25,000 ft Yes planning 2 2 F/A-18C 29 31,000 10,000 Unknown Yes planning 3 3 F/A-18C 33 30,000 10,000 Unknown Yes planning 4 4 F/A-18C 30 31,000 10,000 20,000 ft Yes planning 5 5 F/A-18F 30 37,000 12,000 21,000 ft Yes planning 5 6 F/A-18F 40 37,000 12,000 21,000 ft Yes planning 6 7 F-16A 41 41,000 15,000 28,000 ft No staging 7 8 F/A-18 30 37,000 15,000 25,000 ft No staging 7 9 F/A-18 26 37,000 15,000 25,000 ft No staging RDE Aviator A/C Age Altitude (MSL) Pre-event Cabin Altitude (MSL) Post-event Cabin Altitude (MSL) Sx? Room used for preflight briefing 1 1 F/A-18E 37 40,000 15,000 25,000 ft Yes planning 2 2 F/A-18C 29 31,000 10,000 Unknown Yes planning 3 3 F/A-18C 33 30,000 10,000 Unknown Yes planning 4 4 F/A-18C 30 31,000 10,000 20,000 ft Yes planning 5 5 F/A-18F 30 37,000 12,000 21,000 ft Yes planning 5 6 F/A-18F 40 37,000 12,000 21,000 ft Yes planning 6 7 F-16A 41 41,000 15,000 28,000 ft No staging 7 8 F/A-18 30 37,000 15,000 25,000 ft No staging 7 9 F/A-18 26 37,000 15,000 25,000 ft No staging DISCUSSION Physiological events carry a high risk of aviation mishap due to pilot distraction and disorientation, and can lead to permanent medical disability. It is important, therefore, to continue investigation into etiology of PEs, such as DCS, to advance prevention and treatment modalities. This series describes seven RDEs involving nine aviators that occurred at one air base in Nevada over nine months. Six of these aviators developed symptoms consistent with DCSs. After the seven RDEs occurred, aircraft maintenance (including oxygen systems, flight regimens, maintenance records), and medical histories were investigated without significant findings. However, a high level of indoor CO2 in the briefing spaces, secondary to four non-functioning HVAC systems, was discovered. Is it possible that pre-breathing poor quality air, high in relative CO2 concentration, could have contributed to their symptoms? The role of nitrogen gas in DCS was established in the 1960s.3 Webb and Pilmanis used a pre-breathing mixture to induce DCS and to help identify nitrogen as a causative substance for DCS.3 Subjects exposed to a 50:50 mixture of nitrogen:oxygen were more likely to develop DCS symptoms while subjects exposed to 100% oxygen alone did not.3 The role of CO2 in DCS, however, was argued by Mano and D’Arrigo stemming from an observational study of caisson workers.8 Divers that were exposed to a non-ventilated recompression chamber as part of their 3 atm dive increased their DCS occurrence from 1.65% to 3.04%.8 They argue that CO2 itself was likely the cause of the increased DCS occurrences due to the higher solubility of CO2, and its higher prevalence in aqueous tissue. To further this point, in vitro animal studies looking at DCS showed high levels of CO2, and less-than expected nitrogen found in gas emboli of animal models.9 They argue that CO2 may be more of a cause of DCS over other atmospheric gases.9 Carbon dioxide demonstrates dose dependent neurotoxic effects to include headache, neurologic deficits, posture flexion, seizure, and syncope in healthy subjects when exposed to acute toxic levels.4 Therefore, the Occupational Safety and Health Administration (OSHA) regulates the amount of indoor CO2 exposure to 5,000 ppm maximum over an 8 hour workday.10,11 However, this maximum limit has come into question with toxic effects seen at lower levels. Satish and colleagues demonstrated toxic effects of indoor CO2 levels as low as 1,000 ppm.10 When subjects were tasked with 9 levels of decision-making (basic activity, applied activity, task orientation, initiative, information usage, breadth of approach, and basic strategy), they had a statistically significant 11–23% decline in performance on seven of the nine levels compared to those exposed to CO2 of 600 ppm.10 This decline continued at 2,500 ppm to 44–94%.10 Is it possible that the elevated CO2 measured would lead to an increased risk of DCS? Given the timeline from pre-flight CO2 exposure and the aviators’ RDE was 1–2 hours, a multiple step physiologic response would have to provide an explanation, such as a CO2-induced pro-inflammatory cascade. CO2 is an independent risk factor for inflammation in lung tissue in vitro.5,9 Abolhassani demonstrated a dose-dependent increase of transcription (RNase protection assay) and secretion (ELISA) of pro-inflammatory cytokines, particularly macrophage inflammatory protein-1 alpha.5 Furthermore, exposure to 15 minutes of 40% CO2 with preserved oxygen and nitrogen partial pressures in a rat model was able to identify changes in mRNA and enzyme activity in the frontal and hippocampal regions compared to control rat models. This has led to the understanding of likely CO2-dependent gene expression changes which is not necessarily due to changes in available oxygen.9 Central nervous system inflammation in aviators subjected to high altitude has been demonstrated. Magnetic resonance imaging (MRI) studies have been able to identify white matter hyper intensities (WMH) in symptomatic and asymptomatic pilots.6 Due to the possibility of confounding variables such as acceleration forces, radiation exposure, and other elements of aviation,7 McGuire and colleagues completed a similar MRI-based study using chamber technicians exposed to non-hypoxic, hypobaric conditions who were compared to age matched controls.7 They found a statistically significant difference in WMH in the chamber technicians.7 The study concluded that the WMH were consistent with a “pattern of damage produced by interaction between micro emboli in cerebral tissue, leading to thrombosis, coagulation, inflammation, and/or activation of innate immune response”.7 In that study, the predominance of gene expression differences occurred in the frontal region which correlated with the predominant lobe of the McGuire findings in U-2 pilots.7 This report is far from an answer, but does demonstrate an interesting case series which draws some questions about CO2’s role in these aviators’ symptoms. Other explanations are certainly plausible, such as the accuracy of DCS diagnosis, other environmental exposures, and differences in aircraft and on-board oxygen generation systems. The reported aviators may have been exposed to other contaminates found in poor air quality which is argued in Erdmann and Apte’s report on low level CO2 inducing lower respiratory symptoms.12 For a better understanding, the role of environmental CO2 and pre-flight exposure as a risk of DCS should be reviewed further, including serum levels of CO2 and inflammatory markers in symptomatic aviators. CONCLUSION PEs are a growing safety concern for the aviation community in the military. As such, increasing measures are taken to ensure safety of flight and completion of the mission. To date, there is no correlation of CO2 exposure and altitude DCS. This case series presents findings whereby aviators exposed to elevated levels of CO2 developed PE symptoms requiring treatment, while those who had a normal ventilated briefing space did not. This retrospectively collected data does not provide adequate evidence for a causative factor, but instead presents an interesting case that prompts questions about CO2’s role in DCS. REFERENCES 1 Swift SH : Comprehensive Review of the T-45 and FA-18 Physiological Episodes [Memorandum] . Pearl Harbor, Hawaii , United States Pacific Fleet, Department of Defense , 2017 Retrieved from http://www.navy.mil/local/pes/Comprehensive%20Review%20PE.pdf. 2 Vann RD , Butler FK , Mitchell SJ , Moon RE : Decompression illness . Lancet 2010 ; 377 : 153 – 64 . Google Scholar Crossref Search ADS 3 Webb JT , Pilmanis AA : Fifty years of decompression sickness research at Brooks AFB, TX: 1960-2010 . Aviat Space Environ Med 2011 ; 82 ( 5, Suppl. ): A1 – A25 . Google Scholar Crossref Search ADS PubMed 4 Permentier K , Vercammen S , Soetaert S , Schellemans C : Carbon dioxide poisoning: a literature review of an often forgotten cause of intoxication in the emergency department . Int J Emerg Med 2017 ; 10 ( 1 ): 14 . doi:10.1186/s12245-017-0142-y . Google Scholar Crossref Search ADS PubMed 5 Abolhassani M , Guais A , Chaumet-Riffaud P , Sasco AJ , Schwartz L : Carbon dioxide inhalation causes pulmonary inflammation . Am J Physiol Lung Cell Mol Physiol 2009 ; 296 ( 4 ): L657 – 65 . doi:10.1152/ajplung.90460.2008 . Google Scholar Crossref Search ADS PubMed 6 McGuire S , Sherman P , Profenna L , et al. : White matter hyperintensities on MRI in high-altitude U-2 pilots . Neurology 2013 ; 81 ( 8 ): 729 – 35 . doi:10.1212/WNL.0b013e3182a1ab12.6(5):719-26. ; doi:10.1002/ana.24264 . Google Scholar Crossref Search ADS PubMed 7 McGuire SA , Sherman PM , Wijtenburg SA , et al. : White matter hyperintensities and hypobaric exposure . Ann Neurol 2014 ; 76 : 719 – 26 . Google Scholar Crossref Search ADS PubMed 8 Mano Y , D’Arrigo JS : Relationship between CO2 levels and decompression sickness: implications for disease prevention . Aviat Space Environ Med 1978 ; 49 ( 2 ): 349 – 55 . Google Scholar PubMed 9 Armstrong HG Analysis of gas emboli. Engineering Section Memorandum Report EPX-17-54-653-3. Wright Field, Oh. 10 Satish U , Mendell MJ , Shekhar K , et al. : Is CO2 an Indoor Pollutant? Direct Effects of Low-to-Moderate CO2 Concentrations on Human Decision-Making Performance . Environ Health Perspect 2012 ; 120 ( 8 ): 1671 – 7 . Google Scholar Crossref Search ADS PubMed 11 OSHA (Occupational Safety and Health Administration) . Sampling and Analytical Methods: Carbon Dioxide in Workplace Atmospheres. 2012. Available: http://www.osha.gov/dts/sltc/methods/inorganic/id172/id172.html [accessed 20 March 2019]. 12 Erdmann CA , Apte MG : Mucous membrane and lower respiratory building related symptoms in relation to indoor carbon dioxide concentrations in the 100-building BASE dataset . Indoor Air 2004 ; 14 ( Suppl 8 ): 127 – 34 . Google Scholar Crossref Search ADS PubMed © Association of Military Surgeons of the United States 2019. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)
TI - Elevated Environmental Carbon Dioxide Exposure Confounding Physiologic Events in Aviators?
JF - Military Medicine
DO - 10.1093/milmed/usz092
DA - 2019-12-01
UR - https://www.deepdyve.com/lp/oxford-university-press/elevated-environmental-carbon-dioxide-exposure-confounding-physiologic-97e01ExBd3
SP - 1
VL - Advance Article
IS - 
DP - DeepDyve
ER -