Aerospace Physiology - UMD

Aerospace PhysiologyPrinciples of Space Systems Design

U N I V E R S I T Y O FMARYLAND

Aerospace Physiology

• Cardiopulmonary Physiology– Respiratory– Cardiovascular

• Musculoskeletal• Vestibular• Neurological• Environmental Effects

© 2004 David L. Akin - All rights reservedhttp://spacecraft.ssl.umd.edu



The Human Circulatory System



Lung Measurements

From Roy DeHart, Fundamentals of Aerospace Medicine, Lea & Febiger, 1985



Blood Pressure in Circulatory System



Gas Exchange in the Lungs




Gas Exchange in the Tissues




Metabolic Processes

• Respiratory Quotient (“RQ”)

• Function of activity and dietary balance– Sugar:– Protein:– Fat:

• For well-balanced diet, RQ~0.85



Respiratory Problems

• Hypoxia– Hypoxic– Hypemic– Stagnant– Histotoxic

• Hyperoxia• Hypocapnia• Hypercapnia



Types of Hypoxia• Hypoxic (insufficient O2 present)

– Decompression– Pneumonia

• Hypemic (insufficient blood capacity)– Hemorrhage– Anemia

• Stagnant (insufficient blood transport)– Excessive acceleration– Heart failure

• Histotoxic (insufficient tissue absorption)– Poisoning



Alveolar Pressures

From Roy DeHart,Fundamentals ofAerospace Medicine, Lea &Febiger, 1985



Effects of Supplemental Oxygen




Hypoxia Effective Performance Time

From RoyDeHart,Fundamentalsof AerospaceMedicine, Lea& Febiger,1985



Oxygen Toxicity




Gravity Effects on Arterial Pressure

120/80 mmHg

95/55 mmHg

210/170 mmHg

320 mm

1200 mm

1000 mmH2O = 74.1 mmHg



The Human Circulatory System, Revisited



Cardiovascular Effects of Microgravity

• Cardiovascular deconditioning• Upper body blood pooling• Changes in blood volume• Increased calcium content



Acceleration Effects on Arterial Pressure

120/80 mmHg

25/–– mmHg

475/435 mmHg

320 mm

1200 mm

At 4 g’s longitudinal:1000 mmH2O = 296 mmHg



Decompression Sickness

• Release of dissolved gases in blood followingpressure drop

• “DCS”, “Caisson Disease”, “The Bends”• J. B. S. Haldane modeled DCS as

supersaturation of dissolved nitrogen in blood:

• Experience indicates symptomatic DCS onset atlevels of 1.6-1.8



Haldane Tissue Model

• Hypothesized that tissues absorb andrelease dissolved gases at exponentialrates

• Response to a step change in alveolarpressure



Tissue Models, continued

• Rate coefficient frequently given as timeto evolve half of dissolved gases:

• Workman added concept of “M-values” -critical saturation limits for tissues

• Continued refinement of tissue models forpredicting onset of DCS



PADUA (Univ of Pennsylvania) Tissue Model

1.459480101.49032091.49024081.52016071.55012061.5818051.6114042.0672032.5541023.04051

M0 (bar)T1/2 (minutes)Tissue



Tissue Saturation following Descent



Tissue Saturation after Ascent



Bubble Formation and Growth

• In equilibrium, external pressure balanced byinternal gas pressure and surface tension

• Surface tension forces inversely proportional toradius



Vestibular System




Vestibular Sense Organs




Otolith Responses




Artificial Gravity



Allowable Rotation Rates

• Select groups (highly trained, physicallyfit) can become acclimated to 7 rpm

• 95% of population can tolerate 3 rpm• Sensitive groups (elderly, young, pregnant

women) may have tolerance levels as low as1 rpm



Short-Term Dose Radiation Effects• 10-50 rem - minor blood changes• 50-100 rem

– 5-10% minor nausea and vomiting• 100-200 rem

– 25-50% nausea and vomiting– 50% reduction in lymphocytes

• 200-350 rem– Nausea, vomiting, diarrhea, minor hemorrhage– 75% reduction in all blood cells– 5-50% incidence of death



Short-Term Dose Radiation Effects

• 350-550 rem– Nausea, vomiting, diarrhea, hemorrhage, emaciation– 75% reduction in all blood cells– 50-90% mortality within 6 weeks– 6 month convalescence

• 550-750 rem– Nausea and vomiting within four hours– Mortality approaching 100%

• 750-2000 - survival time <2 weeks• 2000+ - incapacitation within hours



NASA Radiation Dose Limits



References• R. L. DeHart, ed., Fundamentals of Aerospace Medicine, Second

Edition Williams and Wilkins, 1996• A. E. Nicogossian, C. L. Huntoon, and S. L. Pool, Space Physiology

and Medicine, Third Edition Lea and Febiger, 1994• A. E. Nicogossian, S. R. Mohler, O. G. Gazenko, and A. I.

Grigoriev, eds., Space Biology and Medicine (Volume III, Book 1:Humans in Spaceflight) American Institute of Aeronautics andAstronautics, 1996

• J. T. Joiner, ed., NOAA Diving Manual: Diving for Science andTechnology, Fourth Edition Best Publishing, 2001

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Aerospace Physiology - UMD