Lungs At Depth Flashcards
(37 cards)
1 bar
1000 millibars
1 atmosphere absolute (ATA)
1 bar
760 mmHg/ torr
10 m of sea water (msw)
33.08 feet of sea water (fsw)
101.3 kPa
14 psi
10 m depth =
2 atm
As you go down every 10 m, atm increases by,,,
1
10m = 1 ata
Boyle’s law
At a constant temperature the absolute pressure of a fixed mass of gas is inversely proportional to its volume
Applications
-barotrauma
-arterial gas embolism
-gas supplies
Boyle’s law equation
At constant temperature (K)
P1V1=P2V2
Total lung capacity in a 23 year old female diver is
8 litres at the surface. What will this volume be at
160m of seawater during breath hold diving?
P1V1=P2V2
1.0 x 8.0 = 17 x V2
V2 = 8.0 / 17 = 0.470 litres
ATA at a depth of 150m =
16
Henry’s law
The amount of a gas dissolved in a liquid at a given temperature is directly proportional to the partial pressure of the gas
ATA at surface level (0m) =
1
Effects of Henry’s law
Proportionally more gas dissolves in the tissues at depth
If ascend at rate that exceeds body’s capacity to clear this excess gas, inert bubbles may form in the tissues leading to decompression illness
Diving respiratory gas exchange - apnoea diving (holding breath)
diver inhales, pre - hyperventilation
diver descends holding breath, gas compresses
PaO2, PaN2, PaCO2 rise
minimal N2 absorption, but “Taravana”
eventually CO2 builds up sufficiently to induce desire to breathe
diver returns to surface and PO2, PN2, PCO2 fall
Physiological changes of apnoea diving- diving reflex
diving reflex:
-apnoea (stop breathing)
-bradycardia
-peripheral vasoconstriction
Open circuit scuba diving
Self contained underwater breathing apparatus
gas on-demand
-gas delivered on inhalation at ambient pressure
Dalton’s law
Total pressure exerted by a mixture of gases is equal to the sum of the pressures that would be exerted by each of the gases if it alone were present and occupied the total volume
Effects of Dalton’s law
At sea level –
partial pressure N2 = 0.78 ata, O2 = 0.209 ata
At 10 msw –
partial pressure N2 = 1.56 ata, O2 = 0.418 ata
Breathing air at 10 msw same PaO2 as breathing 42% O2 at sea level
Pulmonary oxygen toxicity
Lorrain Smith Effect
PiO2 > 0.5 ATA
-100% oxygen -> symptoms in 12 - 24 hrs
-problem with ITU patients
Relief with PiO2 < 0.5 ATA
Unit of Pulmonary Toxic Dose (UPTD) can be calculated
FVC can be useful to monitor
CNS oxygen toxicity
V - Vision (tunnel vision etc)
E - Ears (tinnitus)
N - Nausea
T - Twitching (extremities or facial muscles)
I - Irritability
D - Dizziness
common final (& often the first) sign will be a convulsion
ConVENTID
46 year old diver. 3 hours dive. 30% O2. 130m depth.
Now has shortness off breath, sub sternal pain
and cough.
What has happened?
Very high PiO2 = 0.3 x 14 = 4.2 ata
Pulmonary oxygen toxicity
PiO2 equation
FiO2 x Pgas
Symptoms of pulmonary oxygen toxicity
Cough
Chest pain
Chest tightness
Shortness of breath
Lorrain smith effect
PiO2> 0.5 ATA
Inert gas narcosis
commonest is nitrogen narcosis
worsens with increasing pressure
-first noticed between 30-40 msw
-Increased PiN2
individual variation
influencing factors- cold, anxiety, fatigue, drugs, alcohol and some medications
narcotic potential related to lipid solubility
Signs and symptoms of Inert gas narcosis
10-30m. - Mild impairment of performance
30-50m. - Over confidence, sense of well being
50-70m - Sleepiness, confusion, dizziness
70-90m. - Loss of memory, stupefaction
90+ - Unconsciousness, death
Note: death may occur at much shallower depths
