Lungs At Depth

Question 1

1 bar

Answer 1

1000 millibars

Question 2

1 atmosphere absolute (ATA)

Answer 2

1 bar
760 mmHg/ torr
10 m of sea water (msw)
33.08 feet of sea water (fsw)
101.3 kPa
14 psi

Question 3

10 m depth =

Answer 3

2 atm

Question 4

As you go down every 10 m, atm increases by,,,

Answer 4

1
10m = 1 ata

Question 5

Boyle’s law

Answer 5

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

Question 6

Boyle’s law equation

Answer 6

At constant temperature (K)
P1V1=P2V2

Question 7

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?

Answer 7

P1V1=P2V2

1.0 x 8.0 = 17 x V2

V2 = 8.0 / 17 = 0.470 litres

Question 8

ATA at a depth of 150m =

Answer 8

16

Question 9

Henry’s law

Answer 9

The amount of a gas dissolved in a liquid at a given temperature is directly proportional to the partial pressure of the gas

Question 10

ATA at surface level (0m) =

Answer 10

1

Question 11

Effects of Henry’s law

Answer 11

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

Question 12

Diving respiratory gas exchange - apnoea diving (holding breath)

Answer 12

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

Question 13

Physiological changes of apnoea diving- diving reflex

Answer 13

diving reflex:
-apnoea (stop breathing)
-bradycardia
-peripheral vasoconstriction

Question 14

Open circuit scuba diving

Answer 14

Self contained underwater breathing apparatus
gas on-demand
-gas delivered on inhalation at ambient pressure

Question 15

Dalton’s law

Answer 15

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

Question 16

Effects of Dalton’s law

Answer 16

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

Question 17

Pulmonary oxygen toxicity

Answer 17

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

Question 18

CNS oxygen toxicity

Answer 18

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

Question 19

46 year old diver. 3 hours dive. 30% O2. 130m depth.
Now has shortness off breath, sub sternal pain
and cough.

What has happened?

Answer 19

Very high PiO2 = 0.3 x 14 = 4.2 ata
Pulmonary oxygen toxicity

Question 20

PiO2 equation

Answer 20

FiO2 x Pgas

Question 21

Symptoms of pulmonary oxygen toxicity

Answer 21

Cough
Chest pain
Chest tightness
Shortness of breath

Question 22

Lorrain smith effect

Answer 22

PiO2> 0.5 ATA

Question 23

Inert gas narcosis

Answer 23

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

Question 24

Signs and symptoms of Inert gas narcosis

Answer 24

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

Question 25

67 year old inexperienced diver. 50m sea water
diving on air. Starts to feel cold, euphoric and is unable
to make further dive decisions.

What has happened?

Answer 25

PiN2 = 6.0 x 0.8 = 4.8 ata

Question 26

Decompression illness

Answer 26

N2 poorly soluble- nitrogen bubbles expands in tissue
Ascent —> fall in pressure
—>fall in solubilty
—> gas bubbles

Question 27

Influencing features of inert gas narcosis

Answer 27

Cold
Anxiety
Fatigue
Drugs
Alcohol
Some medications

Question 28

2 types of decompression illness

Answer 28

Type I Cutaneous only
Type II Neurologic

Question 29

Treatment of decompression illness

Answer 29

O2, supportive treatments and urgent recompression

Question 30

Arterial gas embolism (AGE)

Answer 30

Gas enters circulation via torn pulmonary veins
Small transpulmonary pressures can lead to AGE
Normally occur within 15 minutes of surfacing
Urgent recompression

Question 31

Pulmonary barotrauma

Answer 31

Air leaks from burst alveoli:
-Pneumothorax
-Pneumomediastinum
-Subcutaneous emphysema

Question 32

Quick onset of problems following diving <15 mins

Answer 32

Eg arterial gas embolism

Question 33

What sea level % O2 is breathing air at 10 msw equivalent to

Answer 33

10m deep: 1 +(10/10) = 2 atm = double 1 atm at sea level = 21% x 2 = 42% in scuba gear

Question 34

TLC is 7.82L at surface, what will this be at 150m deep when diving

Answer 34

150 m deep: 1 +(150/10) = 16atm = P2
P1V1 = P2V2
1 atm x 7.82L = 16atm x V2
V2 = 489mls

Question 35

Lorrain smith effect

Answer 35

Immediate pulmonary O2 toxicity
PiO2 > 0.5 ATA
Tunnel vision, timitus, convulsions

Question 36

15 mins after resurfacing

Answer 36

Arterial gas embolism
Rapid over expansion of veins —> tears —> bubbles in arteries

Question 37

Inert gas narcosis

Answer 37

Increased pressure—> increased N2 lipid solubility -die at 90m
Rapid ascent - decompression sickness - decrease in pressure—> N2 forms bubbles in circulation
Immediate : bends (rash and joint pain) —> neuro issues