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Design of a 2-Hour Prebreathe Protocol for Space Walks (EVAs) from the International Space Station (ISS)The majority of extravehicular activities (EVAs) performed from the shuttle use a 10.2 psi staged decompression. The International Space Station (ISS) will operate at 14.7 psi, requiring crews to "campout" in the airlock at 10.2 psi. The constraints associated with campout (crew isolation, oxygen usage, and waste management), provided the rationale to develop a 2-hour prebreathe protocol from 14.7 psi. Previous studies on the affect of microgravity and exercise during prebreathe suggested the feasibility of this approach. Various combinations of adynamia (nonwalking subjects), prebreathe exercise doses, and space suit donning options (10.2 vs. 14.7 psi) were analyzed against timeline and consumable constraints. Prospective decompression sickness (DCS) and venous gas emboli (VGE) accept/reject criteria were defined from statistical analysis of historical DCS data, combined with risk management of DCS under ISS mission circumstances. Maximum operational DCS levels were defined based on protecting for EVA capability with two crew members at 95% confidence, throughout ISS lifetime (within the constraints of NASA DCS disposition policy JPG 1800.3). The accept / reject limits were adjusted for greater safety (including Grade IV VGE criteria) based on analysis of related medical factors. Monte-Carlo simulation was performed to design a closed sequential, multi-center laboratory trial, including the capability of rejecting the primary protocol and testing at least one alternate exercise dose, within the 2-hour prebreathe. The 2-hour protocol incorporates 0, breathing for 5 0 min at 14.7 psi, including 10 min dual cycle ergometry at 75%VO(2max). It requires an additional 30 minO2breathing during depress from 14.7 to 10.2 psi, followed by a 30-60 min suit donning break at 10.2 psi/26.5% O2. It concludes with a 40 min in-suit O2 prebreathe. The protocol would be accepted for operations, if the incidence of DCS was less than 15% and Grade IV VGE less than 20%, both at 95% confidence. The above protocol and accept/reject limits were implemented in a multi-center study.
Document ID
20000108920
Acquisition Source
Johnson Space Center
Document Type
Conference Paper
Authors
Gernhardt, M. L.
(NASA Johnson Space Center Houston, TX United States)
Conkin, J.
(Baylor Coll. of Medicine Houston, TX United States)
Foster, P. P.
(Baylor Coll. of Medicine Houston, TX United States)
Pilmanis, A. A.
(Armstrong Lab. San Antonio, TX United States)
Butler, B. D.
(University of Texas Medical School United States)
Fife, C.
(University of Texas Medical School United States)
Vann, R. D.
(Duke Univ. Durham, NC United States)
Gerth, W. A.
(Duke Univ. Durham, NC United States)
Loftin, K. C.
(Wyle Labs., Inc. Huntsville, AL United States)
Dervay, J.
(NASA Johnson Space Center Houston, TX United States)
Waligora, J. M.
(Waligora (J. M.) Houston, TX United States)
Powell, M. R.
(NASA Johnson Space Center Houston, TX United States)
Homick, Jerry L.
Date Acquired
August 19, 2013
Publication Date
January 1, 2000
Subject Category
Man/System Technology And Life Support
Meeting Information
Meeting: ASMA Annual Scientific Meeting
Location: Texas
Country: United States
Start Date: May 14, 2000
End Date: May 18, 2000
Sponsors: Aerospace Medical Association
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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