How Microgravity Influences Accumulation and Inhalation of CO2 in the Spaceflight Breathing Environment

How Microgravity Influences Accumulation and Inhalation of CO2 in the Spaceflight Breathing Environment | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article How Microgravity Influences Accumulation and Inhalation of CO2 in the Spaceflight Breathing Environment Marshall Tabetah This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4445827/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 5 You are reading this latest preprint version Abstract CO 2 bubbles and pockets have plagued astronauts for many decades since the inception of space exploration, with recurrent reports from astronauts of headaches as the main symptom. The first CO 2 monitors were deployed in the International Space Station (ISS) in 2001, and have reported average CO 2 concentrations of ~ 0.5% (or 5000 ppm) in air. Despite the enhancement in performance of CO 2 removal systems that extract CO 2 from ISS cabins to the external environment, CO 2 concentrations that are at least ~ 0.3% have prevailed, causing CO 2 -related symptoms and subclinical changes to physiology. In order to explain the abnormal concentrations of CO 2 in the breathing environment of the astronauts, the authors suggest that there is a build-up of CO 2 that is influenced by the lack of gravity, also termed microgravity, in low Earth orbit (LEO). This suggestion is motivated by the effect of gravity on buoyancy-driven convection that can facilitate the advection of exhaled CO 2 from the breathing envelope of a respirator, preventing its build-up in the breathing envelope. The processes that define the behavior of CO 2 in the breathing environment of a respirator in astronaut-like conditions in the ISS are revealed through simulations of a computational fluid dynamics (CFD) model of a human respirator that exercises breathing over several breath cycles. This modeling effort is unique among research efforts that have studied CO 2 accumulation in the ISS crew habitat, as it accounts for all the main factors that influence the dynamics of CO 2 – the transient nature of breathing, changes in thermodynamic variables in the environment, and, particularly, changes in CO 2 dynamics over several breath cycles. While simulations of several breath cycles in normal gravity show no tendency for CO 2 to accumulate in the breathing environment, accumulation of CO 2 is evident in microgravity, with the inhalation of CO 2 at average concentrations higher than 0.1% (1000 ppm) in air as a possible outcome in some breath cycles. Breathing in such an environment in a prolonged period of time lasting several days inevitably leads to the build-up of CO 2 -related illnesses. Biological sciences/Biophysics Health sciences/Risk factors fresh air inhaled air exhaled air volume fraction (VOF) normal gravity microgravity breath cycle breathing envelope breathing environment computational volume buoyancy thermal body plume nasal opening CO2 Full Text Additional Declarations (Not answered) Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: withdrawn 23 Nov, 2025 Reviewers invited by journal 30 Jul, 2024 Editor assigned by journal 21 May, 2024 Submission checks completed at journal 21 May, 2024 First submitted to journal 19 May, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4445827","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":333673024,"identity":"f8a7e09a-7870-4b45-99d0-21065a345aa9","order_by":0,"name":"Marshall Tabetah","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA1ElEQVRIiWNgGAWjYHACNhCRwA8iecACCQQ1sIEUJUg2kKzF4ACxWnTnNz978PGHXZ7x7R6zD2/bbBj42XMM8GoxO8ZmbjgjIbnY7M4Z45lz29IYJHveENLCYCbNk8CcuO1GjjEzb9thBoMbBG1h/yb9J6E+cfMMsJb/DPaEtfCYSTMkHE7cIAHWcoDBQIKglpxyw56044kz7hwrZpxzLplH4syzAvxaDh/f9uCHTXVi/+zmzQxvyuzk+NuTN+DVggASEIqHSOVIWkbBKBgFo2AUYAAAUVtGbTRPkwIAAAAASUVORK5CYII=","orcid":"https://orcid.org/0000-0002-1651-7659","institution":"Purdue University","correspondingAuthor":true,"prefix":"","firstName":"Marshall","middleName":"","lastName":"Tabetah","suffix":""}],"badges":[],"createdAt":"2024-05-19 23:45:07","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4445827/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4445827/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":63244986,"identity":"9fd86f1d-dc49-4858-930a-ae78678075cf","added_by":"auto","created_at":"2024-08-26 05:35:57","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2080455,"visible":true,"origin":"","legend":"","description":"","filename":"SubmittedCO2AccumulationMicrogravityArticle.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4445827/v1_covered_19215f58-fdd4-4935-b85b-f024e07e8845.pdf"}],"financialInterests":"(Not answered)","formattedTitle":"How Microgravity Influences Accumulation and Inhalation of CO2 in the Spaceflight Breathing Environment","fulltext":[],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":false,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":true,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":true,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"npj-microgravity","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"npjmgrav","sideBox":"Learn more about [npj Microgravity](http://www.nature.com/npjmgrav/)","snPcode":"41526","submissionUrl":"https://submission.springernature.com/new-submission/41526/3","title":"npj Microgravity","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"NPJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"fresh air, inhaled air, exhaled air, volume fraction (VOF), normal gravity, microgravity, breath cycle, breathing envelope, breathing environment, computational volume, buoyancy, thermal body plume, nasal opening, CO2","lastPublishedDoi":"10.21203/rs.3.rs-4445827/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4445827/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eCO\u003csub\u003e2\u003c/sub\u003e bubbles and pockets have plagued astronauts for many decades since the inception of space exploration, with recurrent reports from astronauts of headaches as the main symptom. The first CO\u003csub\u003e2\u003c/sub\u003e monitors were deployed in the International Space Station (ISS) in 2001, and have reported average CO\u003csub\u003e2\u003c/sub\u003e concentrations of ~\u0026thinsp;0.5% (or 5000 ppm) in air. Despite the enhancement in performance of CO\u003csub\u003e2\u003c/sub\u003e removal systems that extract CO\u003csub\u003e2\u003c/sub\u003e from ISS cabins to the external environment, CO\u003csub\u003e2\u003c/sub\u003e concentrations that are at least\u0026thinsp;~\u0026thinsp;0.3% have prevailed, causing CO\u003csub\u003e2\u003c/sub\u003e-related symptoms and subclinical changes to physiology. In order to explain the abnormal concentrations of CO\u003csub\u003e2\u003c/sub\u003e in the breathing environment of the astronauts, the authors suggest that there is a build-up of CO\u003csub\u003e2\u003c/sub\u003e that is influenced by the lack of gravity, also termed microgravity, in low Earth orbit (LEO). This suggestion is motivated by the effect of gravity on buoyancy-driven convection that can facilitate the advection of exhaled CO\u003csub\u003e2\u003c/sub\u003e from the breathing envelope of a respirator, preventing its build-up in the breathing envelope. The processes that define the behavior of CO\u003csub\u003e2\u003c/sub\u003e in the breathing environment of a respirator in astronaut-like conditions in the ISS are revealed through simulations of a computational fluid dynamics (CFD) model of a human respirator that exercises breathing over several breath cycles. This modeling effort is unique among research efforts that have studied CO\u003csub\u003e2\u003c/sub\u003e accumulation in the ISS crew habitat, as it accounts for all the main factors that influence the dynamics of CO\u003csub\u003e2\u003c/sub\u003e \u0026ndash; the transient nature of breathing, changes in thermodynamic variables in the environment, and, particularly, changes in CO\u003csub\u003e2\u003c/sub\u003e dynamics over several breath cycles. While simulations of several breath cycles in normal gravity show no tendency for CO\u003csub\u003e2\u003c/sub\u003e to accumulate in the breathing environment, accumulation of CO\u003csub\u003e2\u003c/sub\u003e is evident in microgravity, with the inhalation of CO\u003csub\u003e2\u003c/sub\u003e at average concentrations higher than 0.1% (1000 ppm) in air as a possible outcome in some breath cycles. Breathing in such an environment in a prolonged period of time lasting several days inevitably leads to the build-up of CO\u003csub\u003e2\u003c/sub\u003e-related illnesses.\u003c/p\u003e","manuscriptTitle":"How Microgravity Influences Accumulation and Inhalation of CO2 in the Spaceflight Breathing Environment","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-08-26 05:27:48","doi":"10.21203/rs.3.rs-4445827/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"withdrawn","date":"2025-11-23T19:43:26+00:00","index":"","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-07-30T10:14:45+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-05-21T12:56:22+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-05-21T12:56:11+00:00","index":"","fulltext":""},{"type":"submitted","content":"npj Microgravity","date":"2024-05-19T23:40:58+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"npj-microgravity","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"npjmgrav","sideBox":"Learn more about [npj Microgravity](http://www.nature.com/npjmgrav/)","snPcode":"41526","submissionUrl":"https://submission.springernature.com/new-submission/41526/3","title":"npj Microgravity","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"NPJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"751af66b-6983-4436-967c-97262c54f398","owner":[],"postedDate":"August 26th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":35333619,"name":"Biological sciences/Biophysics"},{"id":35333620,"name":"Health sciences/Risk factors"}],"tags":[],"updatedAt":"2024-08-26T05:27:49+00:00","versionOfRecord":[],"versionCreatedAt":"2024-08-26 05:27:48","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4445827","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4445827","identity":"rs-4445827","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}