Atmosphere: Pressure and Air

1
Atmosphere Pressure and Air
Camron Gorguinpour Bioengineering
155 Spring 2005
Picture Courtesy of NASA
2
Overview

• Gas Laws
• Units of Pressure
• Reduced-Pressure Environments
• Impacts of Reductions in Air Pressure
• Air and You

3
Boyle's Law P1V1 P2V2 Charles' Law V1/T1
V2/T2
Picture Courtesy of http//www.longcaybelize.com
4

• Dalton's Law
• PTotal Pa Pb Pc ...
• Henry's Law
• X (Pa/PTotal) 100

Picture Courtesy of NASA
5
Graham's Law D a S/v(MW) Fick's Law Vgas a D
(P1 P2) (A/T)
6
(No Transcript)
7
Minimum Pressure Requirements for Survival

• PH2O in the lungs .9 psi
• PCO2 in the lungs .7 - .9 psi
• PO2 in the lungs 1.9 psi
• Minimum Ambient Pressure (with 100 Oxygen)
• 3.6 psi

8
Physiological Problems Due to Reduced Pressures

• Attenuated sound transmission
• Gases may get trapped in cavities (e.g. ears,
  sinuses, lungs)
• Inhibited lung-chest system (problems breathing,
  coughing, etc.)
• No appreciable physiological problems for
  long-term low barometic pressures

9
Impact of Reductions in Air Pressure

• Ears, Sinuses, and Teeth
• Gases are likely to escape without significant
  harm
• Pain may result from blocked airways
• Stomach and Intestines
• Sea-level gas volume is between .05 and .01
  liters
• Expansion of gas can cause cramps, vomiting,
  expulsion of gas, and unconsciousness

10
Impact of Reductions in Air Pressure

• Decompression Sickness
• Caused by inert gases that evolve from solution
  in bodily fluids (water and fat)
• Evolved gases form bubbles in blood vessels and
  tissues
• Bubbles that form in tissues may cause pain
• Bubbles in blood vessels can block circulation

11
How Can We Mitigate Decompression Sickness?

• What Gases Exist within your Bodily Fluids?
• Why are they there?
• In groups of 2 or 3, discuss ways to prevent or
  mitigate the effects of DCS. Turn in your ideas
  on a single sheet of paper.

12
Impact of Reductions in Air Pressure

• Lungs
• Damage to lungs during rapid decompression is the
  critical factor for human survival
• Relative decompression time between the lungs and
  surrounding environment determines the extent of
  lung damage
• Phase of respiration also determines extent of
  lung damage

13
Impact of Rapid Decompression

• My favorite quote from a scientific document
• Some degree of consciousness will probably be
  retained for 9 to 11 seconds... In rapid sequence
  thereafter, paralysis will be followed by
  generalized convulsions and paralysis once
  again...
• Bioastronautics Data Book. 2nd Edition. Chapter 1

14
Relevant Components of Air

• Oxygen
• Carbon Dioxide
• Inert Gases

15
Oxygen Deprivation

• Anoxia and Hypoxia
• General symptoms include cognitive impairment,
  unconsciousness, convulsions, paralysis, death of
  nervous tissue, and death
• Symptoms of Hypoxia range from very subtle to
  extreme
• Brain and sensory organs are particularly
  impacted, due to their dependence on oxygen
  consumption

16
Oxygen Toxicity

• Oxygen Tensions gt 14.7 psi
• General symptoms include nausea, dizziness,
  faintness, convulsions, lung irritation, and
  blindness in infants
• Blood cell fragility and cell wall permeability
  may also change
• Despite these symptoms, hyperbaric oxygen is
  commonly used for medical treatments

17
Things to Know...

• Gas Laws
• Relevance of Gas Laws to physiology.
• What happens to your body when it is
  decompressed?
• Why?
• How can we fix these problems?