Presentation to the IOM 22 June 2015 NASA Evidence Report: Risk of Decompression Sickness Authors: Conkin J, Norcross JR, Wessel JH, Abercromby AFJ, Klein JS, Dervay JP, Gernhardt ML Presenter: Neal W. Pollock, PhD Location: Keck Center Washington DC
1 Disclosure I currently receive NASA research funding for a project that involves many of the individuals listed as co-authors on this evidence report NNX12AG22A - 'Mechanisms of Musculoskeletal-Induced Nucleation in Altitude Decompression'
1. Does the evidence report provide sufficient evidence, as well as sufficient risk context, that the risk is of concern for long-term space missions? Well-established context and clear description of the available evidence supporting intentional extravehicular activity generally good readability excellent expertise of author panel
2. Does the evidence report make the case for the research gaps presented? Many knowledge gaps are described in the document, but the summary (pg. 53-55) is limited to broad conceptual areas only Specific gaps identified in the report: Mechanisms of gas exchange, micronuclei generation and bubble formation across different pressure and gas environments (pg. 4) Break in prebreathe impact (and payback efficacy) (pg. 4/31) Impact of pharmacological practices (e.g., prophylactic aspirin use) (pg. 11) Impact of temperature shifts on inert gas elimination and decompression risk (pg. 12) Efficacy of intermittent recompression to reduce risk of DCS (pg. 16) Impact of delayed treatment (on treatment efficacy and long term health) (pg. 29) Impact of body fat on inert gas uptake, elimination, and decompression risk (pg. 29) Assessment of inter- and intra-individual variability in risk (pg. 32) Impact of ambulation in low pressure environments (i.e., planetary surface) (pg. 35) Extravascular bubble monitoring capability (i.e., throughout EVA) (pg. 42) Hazard of chronic mild hypoxia associated with Exploration Atmosphere (pg. 51) - 8.2 psi suit pressure /34% oxygen breathing environment; very likely not an issue
3. Are there any additional gaps in knowledge or areas of fundamental research that should be considered to enhance the basic understanding of this specific risk? Specific items not described (or incompletely described): Impact of duration of treatment on efficacy of low pressure treatment of symptomatic decompression sickness (i.e., suit overpressure) (pg. 44-47) Impact of under-treatment (i.e., potentially suit overpressure) on chronic health Utility of new or emerging technologies in making lightweight portable recompression chambers viable for use (i.e., as an alternative to more limited suit overpressure) Transpulmonary passage pathway for bubble arterialization (current focus is limited to patent/persistent foramen ovale; pg. 6) - exercise can promote transpulmonary passage Impact of frequently repeated exposures (acclimatization) on decompression risk Impact of deconditioning on decompression safety (and potential interaction with acclimatization) - Potentially very important for planetary missions in deconditioned state Biomarkers of decompression stress - None established beyond bubbles (good negative predictor; weak positive) Technological capability for real-time physiological monitoring of factors related to decompression stress (e.g., intra- and extravascular bubble formation; with a goal of developing adapting systems to manage individual risk over an evolving period)
4. Does the evidence report address relevant interactions among risks? Very difficult with the limited available data Many interactions are extremely complicated e.g., effects of different timing and magnitude of exercise and thermal stressors
5. Is the breadth of the cited literature sufficient? The literature cited is generally well-balanced and reasonable, certainly not misleading, but not exhaustive
Summary and Recommendations Knowledge gaps should be summarized more clearly Broad categories should include operationalized lists, where feasible, to improve utility