The Lungs And Diving Flashcards
Units of pressure
1 bar -1000 millibars
760 mmHg / torr
1 atmosphere absolute (ATA)
10 metres of sea water (msw) means another atmosphere down
33.08 feet of sea water (fsw)
101.3 kilopascals (kPa)
14psi
Every ten metres of sea water results in a further atmosphere
Boyle’s law
At a constant temperature the absolute pressure of a fixed mass of gas is inversely proportional to its volume
P1V1=P2V2
All calculations in Kelvin
Dive type; apnoea
Diver inhales, pre - hyperventilation
Hyperventilate to reduce the CO2 levels- starting with low CO2 levels, reducing the need to take a breath as CO2 levels control whether we take a breath.
As the CO2 rises from a very low level, the diver has absorbed a lot of the oxygen from their alveoli, becoming hypoxic. Therefore if they had not been hyperventilated they would have had to take a breath sooner
Diver descends holding breath, as diver becomes metres under water the air in their lung is compressed
Even though the diver is not actually breathing, the nitrogen in their lung is being compressed so pressure of inspired N2, which is being forced across into the alveolar capillaries, slightly increases so there is a little bot of Nitrogen absorption- Taravana effect
PaO2, PaN2, PaCO2 rise
Minimal N2 absorption, but “Taravana” (decompression sickness)
Eventually CO2 builds up sufficiently to induce desire to breathe
Diver returns to surface and PO2, PN2, PCO2 fall
The diving reflex (if an individual is exposed to hitting cold water suddenly)
Leads to
Apnoea- suspension of breathing
Bradycardia
-reduction in cardiac output as the peripheral chemoreceptors are activated by a reduction in the arterial pressure of oxygen, responsible for slowing heart rate
-The vasoconstriction is associated with a redistribution of the blood flow, which saves O2 for the O2-sensitive organs, such as the heart and brain
Peripheral vasoconstriction
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]
As you go down into a deep dive, the fraction of oxygen decreases and is replaced with gases like helium
Pulmonary Oxygen toxicity
Lorrain Smith Effect
PiO2 > 0.5 ATA
100% oxygen -> symptoms in 12 - 24 hours
Cough, chest tightness, chest pain, shortness
of breath
Also a problem with ITU patients (ICU)
Relief with PiO2 < 0.5 ATA
Unit of Pulmonary Toxic Dose (UPTD) can be calculated
Forced Vital Capacity (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 (and often the first) sign will be a convulsion
ConVENTID
Inert gas Nacrosis
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
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
Decompression illness
Dive, this leads to compression of nitrogen into the tissues which would include skin and nerves. They sit there when the diver is diving. These bubbles are then trapped in skin and nerves and then the diver ascend, boyles law has to be obeyed.
N2 poorly soluble
Ascent leads to
-fall in pressure
-fall in solubilty
-gas bubbles
Types of decompression illness
Type I Cutaneous only
Type II Neurologic
Treatments:
O2, supportive treatments and urgent recompression
Arterial gas embolism- directly as a result of panicked holding breath
Holding breath under shallow water and immediately rising to surface leads to increase in volume of thorax. The air then follows the path of least resistance to get out. This is the pulmonary veins and will then go into the left atrium, left ventricle and then into the brain.
Gas enters circulation via torn pulmonary veins
Small transpulmonary pressures can lead to AGE
Normally occur within 15 minutes of surfacing
Urgent recompression
Pulmonary barotrauma
If the diver doesn’t breathe rapidly after leaving water, Air leaks from burst alveoli:
Pneumothorax
Pneumomediastinum
Subcutaneous emphysema
