Going up or down - Mattijn B up or down.pdf · How high, how deep? Aviation • Feet & mbar ... • Altitude hypoxia ... Going up or down an introduction to pressure physiology

Going up or down

Mattijn Buwalda, anesthesiologist-intensivist

an introduction to the

physiology of pressure

Medical &

Educational

Services

[email protected]

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

Dank voor uw aandacht!

59 [email protected]