| Viet Tran |
Summary: Boyle drank volumes of grog under pressure while Doyle was already toxic as Henry lamented on how his champagne was flat.
Pressure = Force/Area
Pressure
The fundamental variable in hyperbaric & diving medicine is pressure.
"The volume of a gas is inversely proportional to the absolute pressure (if temp constant)"
P1V1 = P2V2
Reality Check
The volume in your lungs at 1 ATA is 6L. Therefore at 2 ATA your lung volume is 3L.
If you were to breathe via SCUBA at 2 ATA you could increase your lung volume to 6L. If you held your breath and surfaced, your lung volume would be 12L (kaboom).
Why is this important?
Underlies the cause of barotrauma and why at surface you have more breathes in the tank than 10m under
Dalton's Law
"The total pressure exerted by a mixed gas is the sum of the partial pressures of each gas"
Pa + Pb + Pc = PT
Partial pressures at depth can be calculated using this law: Partial Pressure = Fraction of Gas x Absolute pressure
Reality Check
At 1 ATA breathing air, O2 = 0.21 ATA = 160 mmHg
At 3 ATA breathing air, O2 = 0.63 ATA = 479 mmHg
Why is this important?
Underlies the reason behind gas toxicity at depth and why O2 under pressure can cause fires
Henry's Law
"The amount of gas (Q) that will dissolve in a liquid is proportional to the partial pressure of the gas above the liquid"
Qx = k x Px
(k = solubility)
This does not describe the time to reach steady state (aka saturation), which is dependant on (among other things):
Reality Check
The partial pressure of Nitrogen at 4 ATA (30m) is 3 times as much as at 1 ATA (surface). Therefore at steady state, there will be 3 times as much nitrogen in your blood.
Why is this important?
As you go deeper, you have more dissolved nitrogen and oxygen (and any other gas) dissolved in your blood. This increases the concentration gradient into the tissues. So when it comes time to surface, the reverse happens and you get the bends.
Other Laws & Principles
Pascal's Principle
Archimedes' Principle
The fundamental variable in hyperbaric & diving medicine is pressure.
- Reference point: Absolute 0 = a vacuum whereas Gauge 0 = local pressure (eg systolic blood pressure of 120mmHg is 120mmHg + 760 mmHg = absolute pressure)
- 1 ATA = 1 bar = 10 mSW = ft SW = 101 kPA = 760 mmHg (NB 1 bar = 700 kPA)
"The volume of a gas is inversely proportional to the absolute pressure (if temp constant)"
P1V1 = P2V2
Reality Check
The volume in your lungs at 1 ATA is 6L. Therefore at 2 ATA your lung volume is 3L.
If you were to breathe via SCUBA at 2 ATA you could increase your lung volume to 6L. If you held your breath and surfaced, your lung volume would be 12L (kaboom).
Why is this important?
Underlies the cause of barotrauma and why at surface you have more breathes in the tank than 10m under
Dalton's Law
"The total pressure exerted by a mixed gas is the sum of the partial pressures of each gas"
Pa + Pb + Pc = PT
Partial pressures at depth can be calculated using this law: Partial Pressure = Fraction of Gas x Absolute pressure
Reality Check
At 1 ATA breathing air, O2 = 0.21 ATA = 160 mmHg
At 3 ATA breathing air, O2 = 0.63 ATA = 479 mmHg
Why is this important?
Underlies the reason behind gas toxicity at depth and why O2 under pressure can cause fires
Henry's Law
"The amount of gas (Q) that will dissolve in a liquid is proportional to the partial pressure of the gas above the liquid"
Qx = k x Px
(k = solubility)
This does not describe the time to reach steady state (aka saturation), which is dependant on (among other things):
- Temperature
- Surface Area of Liquid-Gas interface (which is why you should drink champagne with a flute glass)
- Energy applied
Reality Check
The partial pressure of Nitrogen at 4 ATA (30m) is 3 times as much as at 1 ATA (surface). Therefore at steady state, there will be 3 times as much nitrogen in your blood.
Why is this important?
As you go deeper, you have more dissolved nitrogen and oxygen (and any other gas) dissolved in your blood. This increases the concentration gradient into the tissues. So when it comes time to surface, the reverse happens and you get the bends.
Other Laws & Principles
Pascal's Principle
- A pressure change to one part of a fluid is transmitted without loss to every portion of the liquid
- Reality check: pressure applied to a plunger will create the same pressure at the other end
- Volume is proportional to temperature
- P1/T1 = P2/T2
- Reality check: Colder water = less partial pressure
Archimedes' Principle
- Buoyancy (that is, force exerted by fluid) is equal to the weight displaced
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