Gas Physics

FICK’S LAW Adolf Fick, 1858 Properties of “Ideal” Gases Fick’s law of diffusion of a gas across a fluid membrane: • Gases are composed of molecules whose size is negligible compared to the average distance between them. Rate of diffusion = KA(P2–P1)/D – Gas has a low density because its molecules are spread apart over a large volume. • Molecules move in random lines in all directions and at various speeds. Wherein: – The forces of attraction or repulsion between two molecules in a gas are very weak or negligible, except when they collide. . K = a temperature-dependent diffusion constant. – When molecules collide with one another, no kinetic energy is lost. . A = the surface area available for diffusion. • The average kinetic energy of a molecule is proportional to the absolute temperature. . (P2–P1) = The difference in concentraon (paral • Gases are easily expandable and compressible (unlike solids and liquids). pressure) of the gas across the membrane. • A gas will completely fill whatever container it is in. . D = the distance over which diffusion must take place. – i.e., container volume = gas volume • Gases have a measurement of pressure (force exerted per unit area of surface). – Units: 1 atmosphere [atm] (≈ 1 bar) = 760 mmHg (= 760 torr) = 14.7 psi = 0.1 MPa

Boyles Law Amontons Law

• Gas pressure (P) is inversely proportional to gas volume (V) • Gas pressure (P) is directly proportional to absolute gas • P ∝ 1/V temperature (T in °K) ∴ ↑V→↓P ↑P→↓V ↓V →↑P ↓P →↑V • 0°C = 273°K • P ∝ T • ∴ P V =P V (if no gas is added/lost and temperature is held constant) 1 1 2 2 ∴ ↑T→↑P ↑P→↑T ↓T →↓P ↓P →↓T • ↓V → also ↑density • ∴ P1/T1=P2/T2 (if no gas is added/lost and volume is held constant)

Charles Law ∴ Combined Gas Law

• Gas volume (V) is directly proportional to absolute gas • Combining Boyles, Amontons & Charles Laws: temperature (T in °K) • 0°C = 273°K • ∴ P V /T = P V /T (if no gas is added/lost) • V ∝ T 1 1 1 2 2 2 • P = initial pressure ∴ ↑T→↑V ↑V→↑T ↓T →↓V ↓V →↓T 1 • V1 = initial volume • T = initial absolute temperature • ∴ V1/T1=V2/T2 (if no gas is added/lost and pressure is held constant) 1 • P2 = final pressure

• V2 = final volume

• T2 = final absolute temperature

• Ideal Gas Law: PV=nRT • n = total number of gas molecules in the vessel • R = constant

Heyer 1 Diving Physiology

Gas Exchange: notes

Carbon dioxide (0.03%) Argon (0.93%) Oxygen (20.95%) Partial Pressure (PO2) ~ 0.2 atmospheres Pressure of

” Gas Exchange

Nitrogen (78.09%) Partial Pressure (PN2) ~ 0.8 atmospheres 1.0 Atmosphere Total Pressure diving 1Atmosphere

“ Air (gases) in our atmosphere are heavy and put pressure on us  Diving: potential hazards  Why seals can dive so long Push balloon 10 m Balloon shrinks to half its size at surface! Partial Pressure (P ) ~ 0.4 atmospheres underwater O2 (and avoid the hazards) Partial Pressure (PN2) ~ 1.6 atmospheres 2.0 Atmospheres Total Pressure 2 Atmospheres 2 Pressure of

Gases can diffuse (spread out to less- 10 meters concentrated places) and dissolve in water.

Water is heavy and increases Concentration/ pressure/compresses gasses. High Partial Pressure

Also note: When carbon dioxide (CO2) dissolves in Low Concentration/ water, it creates an acid (carbonic acid  lower pH). Partial Pressure

Free diving & Regulation of the drive to breathe shallow-water blackout

 Free diving = breath-hold diving  Hyperventilate → ↓P in blood → you don’t feel CO2 the need to breathe → dive long & deep.  Diving →↑depth →↑P , so you extract more O O2 2 from air.  With low P in blood, you still don’t feel the need CO2 to breathe.  Ascent →↓depth →↓↓P . O2  ↓P in blood to brain → loss of consciousness  Increasing P decreases pH, O2 CO2 stimulating you to breathe c.f., Fig. 42.28

SCUBA: self-contained underwater SCUBA: self-contained underwater breathing apparatus breathing apparatus Decompression Sickness (Bends) Air Embolism

 SCUBA: breathing air at ambient pressure  SCUBA: breathing air at ambient pressure At depth, lungs filled with air at high pressure  At 30 meters depth, your whole body feels a pressure of 4 atm (1+3) -- including the air in  Ascent →↓depth →↓total pressure. your lungs. ↓P →↑V  Diving →↑depth →↑P . N dissolves in tissues. If holding your breath, lung volume N2 2 overexpands  Ascent →↓depth →↓P (decompress). N2  Alveoli rupture → air bubbles into bloodsream N2 tissues comes out of solution → microbubbles.  If enough microbubbles form, may collect in  Bubbles may lodge in tissues & small vessels tissues & small vessels causing bends. causing stroke, heart attack, etc..

Heyer 1 Diving Physiology

SCUBA: self-contained underwater breathing apparatus Marine Mammal The 3 Rules! Diving Physiology  Don’t panic! You brought air with you — no need to rush Stop! — Breathe! — Think!

 Never hold your breath! if breathing compressed air

 Ascend slowly! Allow your body to adapt gradually Why can they dive so much better than us?

California sea lion

Elephant seal dives: Elephant Seals  Telemetry tagged study

Elephant seal dives: It’s not in the lungs  Swim 90 km/day  Underwater 90% of time  Ave. dive = 24 min — max 2 hr  Lung volume ≈ 4.6% of — with 2.5 min surface intervals body volume for all  Dives ave. 400+ meters — max 1500 mammals -- including meters marine mammals.

 Marine mammals don’t rely on the air in their lungs while underwater.

Heyer 2 Diving Physiology

Use oxygen slowly: Marine mammals have The Diving Reflex: 2 kinds of tricks:  Heart rate slows  Use oxygen slowly.  Blood pressure decreases  Store a lot of oxygen.  Peripheral circulation decreases  Spleen shrinks: more blood into circulation

Store a lot of oxygen: Why can they dive so much better than us?  Large blood volume Why don’t they get  High concentration of red cells air embolisms? Why don’t they get  High concentration of hemoglobin in red cells the bends?  High concentration of Why don’t they get myoglobin in muscle shallow water blackout?

Heyer 3 c.f., Fig. 42.29

O2 & CO2 diffuse from high concentration to low concentration.