Alterations in Human Physiology. The Human in Space: Clarence F. Sams, Ph.D. NASA/JSC

Transcription

1 The Human in Space: Alterations in Human Physiology Clarence F. Sams, Ph.D. NASA/JSC

2 Adaptations to Long-Duration Space Flight Ocular intraocular pressure in flight retinal blood vessel constriction postflight visual motor task performance contrast discrimination visual field postflight intraocular pressure postflight Cardiovascular resting heart rate stroke volume early in flight PACs & PVCs fluid volume orthostatic tolerance aerobic & anaerobic capacity resting blood pressure postflight central venous pressure (indirect) cardio/thoracic (CK) ratio postflight Musculoskeletal/Bone muscle mass muscle endurance & strength bone mineral content bone integrity Neurosensory vestibular disturbances space motion sickness early in flight postural stability sensorimotor function Body Fluids hemoglobin & hematocrit postflight total body water plasma & urine volumes postflight Electrolytes urinary Ca, PO 4 postflight plasma K & Mg postflight urinary Na, K, Cl, Mg Hormones plasma ADH, ANF urinary aldosterone urinary ADH, cortisol postflight urinary epinephrine, androsterone postflight plasma ACTH, aldosterone, cortisol Metabolites plasma glucose, creatinine, BUN postflight albumin, cholesterol, triglycerides, uric acid

3 Impacts of Physiological Adaptation Space flight-induced changes can affect operations during flight or crew function upon return to Earth Nominal or contingency return and egress Functional operations capability (EVA, etc) Rapid return to function in terrestrial gravity They may also be deleterious to long term crew health These factors must be thoroughly understood and mitigated where possible in order to manage mission and crew health risks

4 Specific Space-Physiology Disciplines for Today's Briefing Bone Neurovestibular Nutrition Immunology

5 BONE ISSUE FOR SPACEFLIGHT Weakening of the bones due to the progressive loss of bone mass is a potentially serious side-effect of extended spaceflight Studies of cosmonauts and astronauts who spent many months on space station Mir revealed that space travelers can lose (on average) 1 to 2 percent of bone mass each month Spacefarers typically experience bone loss in the lower halves of their bodies, particularly in the lumbar vertebrae and the leg bones. Diminishing bone mass also triggers a rise in calcium excretion in urine, which can increase the risk of kidney stones.

6 What is wrong? Bones are dynamic living tissues that constantly reshape themselves in response to the stresses placed on them Two cell types, "osteoblasts" and "osteoclasts" are constantly building or destroying bone. Usually these actions balance each other out. In prolonged weightlessness, bone mass decreases because the lack of stress on the bones alters the balance between bone resorption and bone formation. This altered balance favors resorption and results in a net loss of bone mass.

7 Blood biochemical markers of bone metabolism: Used to estimate rate of bone loss, bone metabolism Suggest that bone degradation is increased, formation is uncoupled from resorption. Bone Formation Bone Resorption

8 Overall bone loss rates of 1-1.5% per month in wt bearing bones Trabecular bone loses mineral significantly faster than the cortical bone (approx 2X) Overall bone density slow to recover Recovered structure not the same as original and may have less total strength Trochanter Femoral Neck Overview of BMD Cancellous Spongy Bone/Trabecular Bone PROXIMAL FEMUR VERTEBRAL BODY Trochanter BMD of ISS & Mir Crewmembers Loss0=7.4% Recovery Half-life=276 life=276 d BMD deficit (% Loss) Cortical Bone/ Compact Bone Med ops taking several actions based on these findings: Aggressive use of on-orbit countermeasures Following crew for longer post-flight with DXA and QCT Developing a strategy for FEA modeling to determine strength levels Further research collaborations to determine long term fracture risks Days-After-Landing

9 Central Nervous System Integrates Multiple Sensory Inputs to Control Movement 9

10 Sensorimotor Disturbances Occur During and After G-transitions Transit Transit Earth Preflight Planetary Surface Earth Postflight Operations G-transitions G-transitions ISSUES: Postural and gait instability Visual performance changes Manual control disruptions Spatial disorientation Motion sickness OPERATIONAL IMPACT: Vehicle control Vehicle egress Planetary EVAs 10

11 Functional Mobility Test Data: Evaluates Loco-motor control Time to Complete Course Recovery of functional mobility to 95% of preflight level took 15 days. N = 18 Mulavara AP, Feiveson A, Feidler J, Cohen HS, Peters BT, Miller CA, Brady R, Bloomberg JJ. Experimental Brain Research. 202(3):

12 Sensorimotor Countermeasures Training for incongruent stimuli the brain can learn to better tolerate mixed CNS signals (A) Adaptability Training: Enhance ability to adapt to novel gravitational environments (B) Sensory Supplementation: Use alternate sources of sensory information to provide feedback during adaptive phases. (C) Artificial Gravity: Short radius, intermittent exposure

13 Nutrient Requirements Energy CHO (fiber), Fat, Protein Fat-soluble vitamins Water-soluble vitamins Minerals Fluid Countermeasures Energy Amino acids Protein Sodium Fatty acids Antioxidants Other Space Nutrition Bisphosphonates KCitrate Other Meds Exercise Other Systems Bone Muscle Cardio Fluid/Electrolyte Immunology Hematology Neurovestibular Endocrine GI BHP Vision Vehicle/Mission Duration Food System Radiation EVA Schedule Nutrition is critical for any type of exploration mission, and is multifaceted.

14 Dietary Intake Maintaining dietary intake during flight is very important. Inadequate intakes are associated with greater bone and muscle loss, altered cardiovascular performance, and other health risks. Intake for ISS crewmembers is tracked with a computer-based Food Frequency Questionnaire (above).

15 Omega-3 Fatty Acids Fish intake is associated with lower bone loss. Fish, and omega-3 fatty acids in particular, may mitigate bone and muscle loss, cardiovascular, and cancer risks.

16 Vitamin D Vitamin D intake is critical for astronauts, where the food system does not provide adequate amounts, and the crews are shielded from ultraviolet light. Supplementation with 800 IU vit D/day maintains status during flight (left panel). Antarctic studies show vitamin D, stress, and viral reactivation are interrelated.

17 THE IMMUNE SYSTEM One of larger tissues in the human body and exists in a highly distributed state. Consists primarily of white blood cells (WBCs) located in lymph nodes and the peripheral blood. Responsible for protection against viral and bacterial infection, latent viral reactivation, tumor surveillance, wound healing, etc. Dysregulation can result in increased infection rate, malignancy, autoimmunity, allergy, etc.

18 In-flight cell culture -Intracellular signaling, cytoskeleton rearrangement, microtubule organizing center orientation, generalized proliferative responses all altered during flight. Reactivation of latent herpesviruses -EBV, CMV, VZV reactivation during flight -Infectious VZV particles secreted in saliva Short duration Long duration Humoral immunity -Immunization with antigen generates normal antibody response during flight (MIR-18) Reduced cell mediated immunity -CMI Multitest, common recall antigens, long duration flight Post-flight observations -Altered circulating leukocyte distribution Altered cytokine production patterns (secreted, intracellular, Th1/Th2) -Decreased NK cell function -Decreased granulocyte function -Decreased T cell function* -Altered immunoglobulin levels -Latent viral reactivation -Altered virus-specific immunity -Expression of EBV IE/late genes* -Altered neuroendocrine responses *Post-flight observations differ between long vs. short duration space flight.

19 Overview: Spaceflight-Associated Immune Dysregulation

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