Aerospace Physiology. Lecture #11 Oct. 7, 2014 Cardiopulmonary physiology. Musculoskeletal Vestibular Neurological Environmental Effects MARYLAND

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2 The Human Respiratory System 2

3 Lung Measurements From Roy DeHart, Fundamentals of Aerospace Medicine, Lea & Febiger,

4 Respiratory Volume vs. Exertion 4

5 Metabolic Processes Respiratory Quotient ( RQ )!! RQ = Exhaled volume of CO 2 Inhaled volume of O 2 Function of activity and dietary balance Sugar: C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O ( RQ =1.0) Protein: 2C 3 H 7 O 2 N + 6O 2 5CO H 2 O ( RQ = 0.83) Fat: C 57 H 104 O O 2 57CO H 2 O ( RQ = 0.71) For well-balanced diet, RQ~0.85 5

6 The Human Circulatory System 6

7 Blood Pressure in Circulatory System 7

8 Gas Exchange in the Lungs From Roy DeHart, Fundamentals of Aerospace Medicine, Lea & Febiger,

9 Gas Exchange in the Tissues From Roy DeHart, Fundamentals of Aerospace Medicine, Lea & Febiger,

10 Respiratory Problems Hypoxia Hypoxic Hypemic Stagnant Histotoxic Hyperoxia Hypocapnia Hypercapnia 10

11 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 11

12 Pressure Effects on Blood Oxygenation From Roy DeHart, Fundamentals of Aerospace Medicine, Lea & Febiger,

13 Pressure Effects on Blood Oxygenation From Roy DeHart, Fundamentals of Aerospace Medicine, Lea & Febiger,

14 Effects of Supplemental Oxygen From Roy DeHart, Fundamentals of Aerospace Medicine, Lea & Febiger,

15 Hypoxia Effective Performance Time From Roy DeHart, Fundamentals of Aerospace Medicine, Lea & Febiger,

16 Lung Overpressure Following Decompression From Nicogossian and Gazenko, Space Biology and Medicine - Volume II: Life Support and Habitability, AIAA

17 Oxygen Toxicity From Roy DeHart, Fundamentals of Aerospace Medicine, Lea & Febiger,

18 Effects of ppco2 From James T. Joiner, NOAA Diving Manual, Fourth Edition,

19 Acute Effects of Hyperventilation From James T. Joiner, NOAA Diving Manual, Fourth Edition,

20 Gravity Effects on Arterial Pressure 320 mm 95/55 mmhg 120/80 mmhg 1200 mm 1000 mmh 2 O = 74.1 mmhg 210/170 mmhg 20

21 The Human Circulatory System, Revisited 21

22 Cardiovascular Effects of Microgravity Cardiovascular deconditioning Upper body blood pooling Changes in blood volume Increased calcium content 22

23 Acceleration Effects on Arterial Pressure 320 mm 25/ mmhg 120/80 mmhg 1200 mm At 4 g s longitudinal: 1000 mmh 2 O = 296 mmhg 475/435 mmhg 23

24 Supersaturation of Blood Gases Early observation that factor of two (50% drop in pressure) tended to be safe Definition of tissue ratio R as ratio between saturated pressure of gas compared to ambient pressure P N2 R = =0.79 (nominal Earth value) P ambient 50% drop in pressure corresponds to R=1.58 (R values of ~1.6 considered to be safe ) 24

25 Tissue Models of Dissolved Gases Issue is dissolved inert gases (not involved in metabolic processes, like N2 or He) Diffusion rate is driven by the gradient of the partial pressure for the dissolved gas!! dp tissue (t) dt = k [P alveoli (t) P tissue (t)] where k=time constant for specific tissue (min -1 ) P refers to partial pressure of dissolved gas 25

26 Solution of Dissolved Gas Differential Eqn. Assume ambient pressure is piecewise constant (response to step input of ambient pressure) Result is the Haldane equation: P tissue! (t) =P tissue (0) + [P alveoli (0) P tissue (0)] 1 e kt Need to consider value of P alveoli P! alveoli =(P ambient P H2O P CO2 + P O2 P! alveoli = P ambient P H2O + 1 RQ ) Q RQ P CO2 Q where Q=fraction of dissolved gas in atmosphere ΔP O2 =change in ppo2 due to metabolism 26

27 Linearly Varying Pressure Solution Assume R is the (constant) rate of change of pressure - solution of dissolved gases PDE is! 1 R P t (t) =P alv0 + R t P alv0 P t0! k k This is known as the Schreiner equation For R=0 this simplifies to Haldane equation Produces better time-varying solutions than Haldane equation Easily implemented in computer models e kt 27

28 Haldane Tissue Models Rate coefficient frequently given as time to evolve half of dissolved gases:! ln (2) ln (2) T! 1/2 = k = k T 1/2 Example: for 5-min tissue, k= min -1 Haldane suggested five tissue compartments : 5, 10, 20, 40, and 75 minutes Basis of U. S. Navy tables used through 1960 s Three tissue model (5 and 10 min dropped) 1950 s: Six tissue model (5, 10, 20, 40, 75, 120) 28

29 Workman Tissue Models Dr./Capt. Robert D. Workman of Navy Experimental Diving Unit in 1960 s Added 160, 200, 240 min tissue groups Recognized that each type of tissue has a differing amount of overpressure it can tolerate, and this changes with depth Defined the overpressure limits as M values 29

30 Workman M Values Discovered linear relationship between partial pressure where DCS occurs and depth! M = M 0 + M=partial pressure limit (for each tissue compartment) M 0 =tissue limit at sea level (zero depth) ΔM=change of limit with depth (constant) d=depth of dive Can use to calculate decompression stop depth 30 Md d min = P t M 0 M

31 Effect of Multiple Tissue Times 31

32 Physics of Bubbles Pressure inside a bubble is balanced by exterior pressure and surface tension P! internal = P ambient + P surface = P ambient + 2 r where γ=surface tension in J/m 2 or N/m (=0.073 for water at 273 K) Dissolved gas partial pressure P g =P amb in equilibrium Gas pressure in bubble P int >P amb due to γ All bubbles will eventually diffuse and collapse 32

33 Bubble Formation and Growth In equilibrium, external pressure balanced by internal gas pressure and surface tension Surface tension forces inversely proportional to radius 33

34 Historical Data on Cabin Atmospheres from Scheuring et. al., Risk Assessment of Physiological Effects of Atmospheric Composition and Pressure in Constellation Vehicles 16th Annual Humans in Space, Beijing, China, May

35 Spacecraft Atmosphere Design Space from Scheuring et. al., Risk Assessment of Physiological Effects of Atmospheric Composition and Pressure in Constellation Vehicles 16th Annual Humans in Space, Beijing, China, May

36 Effect of Pressure and %O 2 on Flammability from Hirsch, Williams, and Beeson, Pressure Effects on Oxygen Concentration Flammability Thresholds of Materials for Aerospace Applications J. Testing and Evaluation, Oct

37 Atmosphere Design Space with Constraints from Scheuring et. al., Risk Assessment of Physiological Effects of Atmospheric Composition and Pressure in Constellation Vehicles 16th Annual Humans in Space, Beijing, China, May

38 Constellation Spacecraft Atmospheres from Scheuring et. al., Risk Assessment of Physiological Effects of Atmospheric Composition and Pressure in Constellation Vehicles 16th Annual Humans in Space, Beijing, China, May

39 Categories of Sensing Proprioception (internal to body) Self-Sensing Vestibular (inertial forces) Muscle and tendon sensors (extension) Joint sensors (angle) Exteroception (external to body) Visual Auditory Cutaneous 39

40 Anatomy of the Ear From James T. Joyner, ed., NOAA Diving Manual, Best Publishing,

41 Vestibular System From Roy DeHart, Fundamentals of Aerospace Medicine, Lea & Febiger,

42 Vestibular Sense Organs From Roy DeHart, Fundamentals of Aerospace Medicine, Lea & Febiger,

Aerospace Physiology. Lecture #10 Oct. 6, 2015 Cardiopulmonary physiology. Musculoskeletal Vestibular Neurological Environmental Effects MARYLAND

Aerospace Physiology. Lecture #10 Oct. 6, 2015 Cardiopulmonary physiology. Musculoskeletal Vestibular Neurological Environmental Effects MARYLAND Lecture #10 Oct. 6, 2015 Cardiopulmonary physiology Respiratory Cardiovascular Musculoskeletal Vestibular Neurological Environmental Effects 1 2015 David L. Akin - All rights reserved http://spacecraft.ssl.umd.edu