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Going up or down
Mattijn Buwalda, anesthesiologist-intensivist
an introduction to the
physiology of pressure
Medical &
Educational
Services
What to expect…..
• Physics and units
• Pressure effects – Body structure
– Ventilation and circulation
– Air containing spaces
– Partial pressure of gasses
– Solubility of gasses in body tissues
2
Up or down
3
How high, how deep?
Aviation
• Feet & mbar
• 1 ft = 0,3048 m
• Commercial aviation
– 30.000 – 40.000 ft
– (9 – 12 km)
– 100 mbar
Diving
• Meters & bar
• Recreational scuba diving
– < 40 m (5 bar)
• Technical:100 m (11 bar)
• Extreme/ records: 330 m
4
What is pressure?
1 Pascal = 1 N/ m2
F = m x a (a=9.8)
F = m x 10 5
Pressure units
• 1 N/M2 = 1 Pascal (Pa)
• 100 Pa = 1 hecto Pascal (hPa)
• 1 hPa = 1 millibar (mbar)
• 1000 mbar = 1 bar
• 1 bar ≈ 1 atm
1 atmosphere (atm)
(sea level/15oC)
= 1013,25 hPa
= 1013,25 mbar
= 1,01325 bar
= 760 mmHG
= 760Torr
= 14,696 psi 6
A cube on the floor
• Air: 1 M3 = 1,225 kg
• = 12,25 N/M2
• = 12,25 Pascal
• water: 1 M3 = 1000 kg
• = 10.000 N/M2
• = 10.000 Pascal
• = 100 hPa
• = 0.1 bar 7
A Column of air
10.000 kg air = 100.000 N
100.000 n/m2 = 100.000 Pa
1000 hPa = 1000 mbar
= 1 bar 8
Going up
• Air mixture:
• N2 78.1%
• O2 20.8%
• CO2 0.03%
• Trace <0.1%
• H2O 0.1-1%
9
Going up
Non lineair!
Below 5000 ft: 1mb = 27 ft
Above 5000 ft: 1 mb = 35 ft
Above 18000 ft: 1 mb = 50 ft
Average 1 mb = 30 ft ≈ 10 m
Op 5 km > 500 mb
Op 8848 m > 300 mb 10
Standard atmosphere
• Pressure
– 1013.25 hPa at mean
sea level (MSL)
– Decrease 1hPa/ 30 ft
• Temperature
– at MSL = 15o C
– Decrease 2o/ 1000 ft
– Decrease 6.5o / 1000m
• Need for calibration! 11
Going up
• 30 ft/hPa (mb) • recreational aviation (“kleine luchtvaart”)
• mountaineering 12
Going up
• Pressure will decrease
• Non linear
• But….1 hPa / 30 ft (=10m)
• Sea level: 1013 hPa = 1 atm ≈ 1 bar
• 18000ft/ 5.5 km: 500 hPa
• Mt Everest 8848m: 300 hPa
• Standard atmosphere…..
• Air mixture = constant 13
Going down
• water: 1 M3 = 1000 kg
• = 10000 N/M2
• = 10000 Pascal
• = 100 hP
• = 0.1 bar 14
Going down
• Water column 10m high: 1 bar
• At 10 m depth: 1 bar + 1 bar (air column)
15
Going down
• Water is (almost) non compressible
• Depth pressure relation is linear!
• Temperature is not a factor
16
Pressure effects:
• Body structure
– explosive decompression
– HPNS
• Ventilation and circulation
– pressure diuresis
– Dive reflex
– Immersion pulm. edema
– snorkeling
• Air containing spaces (Boyle)
• Partial pressure of gasses (Dalton)
• Solubility of gasses in body tissues (Henry)
17
Explosive decompression in space
18
Explosive decompression in space
• Massive expansion and rupture of lungs
and gas containing digestive tract
• Massive decompression sickness
• Boiling of body liquids!
Total recall 1990
19
HPNS
• High pressure nervous syndrome
• > 150 meter depth
• Individual variation
hand tremors
cramps
nausea
vertigo
loss of coordination
poor sleep
nightmares
Lasts > 12 h after compression
Lt Coffey suffering from HPNS: The Abyss 1989 20
HPNS
• All animals with a CNS
• Increased excitability of CNS
• Increased hydrostatic pressure
• Partial protection:
– N2, barbiturates, N2O, ketamine, C2H5OH
– Anaesthetics!
• Pressure reversal of anaesthetics!
21
HPNS
22
Wetting your wetsuit……
• “duikers plasje”
• Immersion diuresis
• Also during head-out immersion
• Also provoked by prehydration!
• Diuresis x 3 (350 ml/h)
• physiology:
– Centralisation blood volume
– Increased intrathoracic blood volume
– Atrial dilatation > ANP
– Baroreceptor > less ADH 23
Pressure diuresis
24
IPE Immersion Pulmonary Edema
• After 5-10 min diving (shallow or deep) or
swimming
• Dyspnoea, thight feeling, hypoxia, cough
• Pink frothy sputum, pulmonary edema
• Factors: cold, immersion, stress, effort,
age
• Individual predisposition (no more diving!!)
Slade JB, et al. Pulmonary edema associated with scuba diving. Chest 2001; 120:1686-94
Edmonds C. Scuba divers pulmonary oedema. A review. Diving and hyperbaric medicine 2009;39:226-31
25
A very thin layer......
26
IPE
Raised pulmonary
capillary pressure
Sympathetic
tone
Centralization
of blood
volume
Cold
Inspiratory resistence (regulator)
Chest compression (suit/BCD)
Negative intrathoracic
pressure edema
Genetic
predisposition,
e.g. endotheline-1
response
Anxiety &
effort
Dive reflex
Total body
squeeze Age, hidden
ischaemic heart
disease
27
Dive reflex
28
Dive reflex - bradycardia
29
• Max length 40 cm, why?
• Dead space volume + 250 ml!
• At 1 m depth > + 0.1 bar = 1 kg/cm2
• Thoracic surface 600 cm2 > 60 kg!!!
• Negative insp. pressure 100cm H2O!!!
Snorkeling
30
Changing pressure: Boyle’s law P x V = constant
Dalton’s law the total pressure exerted by a gaseous
mixture is equal to the sum of the partial
pressure of each individual component in a
gas mixture.
Henry’s law At a constant temperature, the amount of a
given gas that dissolves in a given type and
volume of liquid is directly proportional to the
partial pressure of that gas in equilibrium with
that liquid.
31
Boyle (p x v = constant)
32
Boyle (p x v = constant)
Diving
• Squeeze:
– Mask squeeze
– Suit squeeze
– Middle ear/ sinus
– Lung squeeze
• Barotraumas:
– Lung overexpansion
– Middle ear/ sinus
– teeth
Aviation
• Middle ear/ sinus
• Teeth
• Gas in the digestive tract
33
Squeeze
34
Equalizing
Difficult clearance after…
35
Barotrauma
36
Dalton
• the total pressure exerted by a gaseous
mixture is equal to the sum of the partial
pressure of each individual component in
a gas mixture.
37
Dalton
(partial)
Pressure
Air
Atmospheric
pressure
N2
78%
O2
21%
Mt Everest 253 mmHg 197 mmHg 53 mmHg
Mean sea level 760 mmHg
592 mmHg 160 mmHg
Mean sea level 1 bar 0.78 bar 0.21 bar
At 40 m depth 5 bar 3.9 bar 1.05 bar
At 60 m depth 7 bar 5.46 bar 1.47 bar
38
Dalton
Diving
Increased partial pressure:
• Nitrogen narcosis
• Oxygen toxicity
Aviation/ mountaineering
Decreased partial pressure:
• Altitude hypoxia
• Hypoxia related
syndromes in
mountaineering
– HAPE
– AMS
39
Nitrogen narcosis
• Similair to inhaled N2O,
Alcohol etc (GABA receptor)
• > 30 m depth (large
variability)
• Some degree of habituation
• Enhanced by: excertion, cold,
fatique, anxiety
• Impaired judgement .... not
harmless!
40
Nitrogen narcosis
Relative narcotic
potency
Molecular weight
Helium 0.23 4
Neon 0.28 20
Hydrogen 0.55 2
nitrogen 1 28
41
Oxygen toxicity
• Cumulative effect = Smith Lorraine effect
– pulmonary toxicity
– pO2 > 0.5 bar
• Acute effect = Paul Bert effect = CNS toxicity
• Symptoms:
– tunnel vision, twitching, nausea,
– dizziness, tinnitus, convulsions
• ± > 1.7 bar partial pressure O2
– decreased CO2 carrying capacity of Hb
– depression cell metabolism
– oxygen radicals Predisposing:
•exercise,
•stress,
•hyperthermia
42
Oxygen toxicity
Active: max pO2 = 1.4
Passive: max pO2 = 1.6
PO2 = 1.4 PO2 = 1.6
21% 56 m 66 m
32% 33 m 40 m
50% 18 m 22 m
80% 7 m 10 m
100% 4 m 6 m
Maximum Operating Depth
Protective (GABA):
Benzo’s, C2H5OH
43
Trimix
• Less N2 to decrease nitrogen narcosis
• Less O2 to minimize risk O2 toxicity
• Example: dive to 110 m!
– O2 10% > pO2 = 1.2
– He 50%
– N2 40%
44
Altitude
hypoxia
45
The oxygen cascade
• dry air: 160 mmHg
• humidified: 150 mmHG
• alveolair: 110 mmHg
• arterial: 100 mmHg
• tissues: 40 mmHg
• intra cellular: 3-4 mmHg:
ppO2 from air to mitochondrion
46
Alveolair gas equation
Sea level > (760-47) x 0.21 - (35:0.8) = 102 mmHg
8000 ft > (532 – 47) x 0.21 - (35:0.8) = 58 mmHg
Cabin pressure
47
Cabin pressure
2-3 mm aluminium alloy 2024 48
Breathing air on Mount E?
Mt Everest (253-47) x 0.21 - (35:0.8) = 0 mmHg !!??
Mt Everest (253-47) x 0.21 - (13:0.8) = 27 mmHg
4 climbers @ 8400m
(272 mmHg)
pH 7.53
paC02 13.3
paO2 24.6
HCO3 10.8
BE -6.9
Sat 54%
pAO2 30
Lactate 2.2
Grocott MPW, et all. Arterial blood gases and oxygen content in climbers on Mount Everest. NEJM 2009;360:140-9
49
Altitude hypoxia
< 5000 ft/ 1500 m No symptoms
> 5000 ft ↓ night vision
↑ hyperventilation
↑ cardiac output
> 10.000 ft headache
dizziness
blurring
eye-hand coordination
> 15.000 ft tunnel vision
slowing mental function
euphoria
aggression
> 20.000 ft coma
50
Time of useful consciousness
www.youtube.com/watch?feature=player_embedded&v=WTNX6mr753w 51
Altitude hypoxia
Legal requirements
• 10.000 – 13.000 ft: max
30 min without oxygen
suppletion
• > 13.000ft: Oxygen
suppletion mandatory
• NL: recreational aviation
mostly < 10.000 ft
52
Henry’s law
Solubility of gas depends on:
•Ambient pressure
•Temperature
•Specific gas
•Specific fluid/tissue 53
54
Tissue halftimes
http://www.philippe.entrance.be/Decompressie/decompressie%20site.htm
55
•Every diver has bubbles!
•Micro nuclei in blood and tissues
•Bubble dynamics
56
Bubbles......
• Every diver has some bubbles in his or her
tissues and venous blood
• Most venous bubbles are filtered in the lung!
• Problems arise if:
– The bubbles get to big and numerous that they
cause tissue distortion and venous blockage
– Appear in the arterial circulation due to:
• pulmonary overload
• lung burst > Arterial gas embolie
• persistent foramen ovale
57
Arterial bubbles
58
