Lungs At Depth Flashcards
What is Apnoea Diving?
Diving profession > 5,000 years old
Usually single breath taken at surface
Breath held throughout immersion
Early efforts less than 100 feet
- Salvage work
- Harvesting food, sponges, coral, and mother-of-pearl
What are the Units of Pressure?
1 bar -1000 millibars
760 mmHg / torr
1 atmosphere absolute (ATA)
10 metres of sea water (msw) - every 10 metres enter a new atmosphere
33.08 feet of sea water (fsw)
101.3 kilopascals (kPa)
What is 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
In Kelvins
What is 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
What are the 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
What are factors of the diving environment?
Hazardous
Physically challenging
Distortion / impairment of special senses
General and specific sources of emotional stress
- Claustrophobia, agoraphobia, marine animals
Hyperbaric environments
What is the Respiratory Gas Exchange during diving?
- 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
What are physiological changes during diving?
diving reflex
- apnoea
- bradycardia
- peripheral vasoconstriction
What is an open circuit scuba?
Self contained underwater breathing apparatus
gas on-demand
- gas delivered on inhalation at ambient pressure
What is 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
What are the 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
What is an octupus?
- additional single hose second stage regulator
- connected to the diver’s first stage regulator
in case primary second stage regulator fails
or for buddy breathing
What is the demand regulator assembly?
- Delivers gas to the diver after reducing the high-pressure gas in the cylinder to a pressure that can be used by the diver
- First Stage reduces the pressure of the gas to a predetermined level over ambient
- Second Stage
Has a movable diaphragm
Is linked by a lever to the low-pressure valve
which leads to a lower-pressure chamber
What is 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
What is 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
