Hyperbaric Flashcards
hyperbaric:
gas at high pressure
Dalton law
the total pressure of a mixture of gases is the sum of their individual partial pressures
composition of air, dry and wet at standard atmospheric pressure of
760mmHg
Dry air: Gas partial pressures =
N2 = 593 O2 = 160 CO2 = 0.23 Ar = 7 H2O = 0
ALL IN mmHG
Wet air: Gas partial pressures
N2 = 557 O2 = 150 CO2 = 0.21 Ar = 6.6 H2O = 47
ALL IN mmHg
concentration of a gas dissolved in a solution can be determined using
Henrys Law
Henrys Law =
[Gas]dis = s X Pgas
s = solubility of coefficient (mM/mmHg) P = partial pressure of the gas
oxygen-haemoglobin dissociation curve at room pressure
- partial pressure of O2 = 100mmHg
- O2 content 20 mlO2/dl blood
every ten metres you dive down barometric pressure increases by
1atm
- so at ten metres down u have 2 times of gas
N2 –>~600mmHg to ~1200mmHG
O2 –> ~160mmHg to ~320mmHg
These gases will dissolve more into the blood
who’s law explains why more gas will dissolve into blood at deep depths
Henrys Law
problems of diving arise when
you come back up
normally partial pressure of CO2 in mixed venous blood =
~46mmHg
following gas exchange pp of CO2 and O2 in alveolar air and at ten metres
CO2 = ~40mmHg O2 = ~100mmHg
they double, so CO2 from the lungs will start to diffuse back into the body, causes increase in arterial CO2
at ten metres down there is a ___ of pressure in the gas in the lungs and ___ in volume
doubling
reduction
At ten metres due to CO2 diffuse back into lungs and metabolic production elevate arterial CO2 this acts on
respiratory centre –> increases urger to breathe. However O2 levels still high enough so compensation to triggered
During return to surface from dive
- pressure in lungs returns to normal
- fall in alveolar CO2 and O2
- causes rapid fall in arterial CO2 and O2
- drop in cerebral O2 can lead to a blackout! (deep water blackout)
in short main problem to avoid in diving
damage to lungs as gas expands, breath out as you rise
__ areas of body are relatively resistant to effects of high pressure
liquid
where do problems with pressure on the body arise:
air spaces: there are no issues if the gas pressures can equilibrate (Barotrauma)
Barotrauma:
injury arising from pressure changes, lungs and ear
ears and pressure:
problems arise if eustachian tube is blocked and doesnt allow gas movements between throat and middle tube
- as u dive down water pressure increases and pushes on ear drum
- ear drum/blood vessels may burst
sinuses and pressure:
- air filled chambers in your head tubes connecting them to throat
- pathways blocked = can’t equilibrate = build up of pressure
- possible bleeding into sinuses
over inflation of the lungs: (coming up and u don’t breath out)
- rupture of alveoli so gas can escape from lungs into the body
- arterial gas embolism
- pneumothorax
- mediastinal and subcutaneous emphysema
pneumothorax =
- collapsed lung due to gas escaping lungs and rests outside lungs and chest wall (normally plasma there)
- expansion of lungs and chest wall is disrupted
arterial gas embolism:
-air can pass into blood vessels, so bubbles of gas in blood = dangerous (brain –> blocks arteriole = stroke / go to heart blocking coronary artery)
Mediastinal Emphysema:
- air bubbles in the tissue around the heart/trachea/large blood vessels
- if this gas expands increase pressure around these organs/vessels
subcutaneous emphysema:
gas bubbles form in the neck, effect blood vessels going to the brain/head
nitrogen narcosis:
- nitrogen almost acting as anaesthetic & alters ion conductance
- symptoms appear at 30m deep, get worse deeper u go, fatal at 90m
- as depths increase the concentration of nitrogen N2 in the blood increases
- N2 higher solubility in lipid than blood
- being ‘drunk’ symptoms
- ‘martini’ effect
prevention of nitrogen narcosis:
- limit depth and duration of dive
- change in gas composition: use gas mixture replacing N2 with helium
oxygen toxicity:
- at atmospheric pressure Hb is almost fully saturated, increasing pressure an extra O2 is dissolved in the plasma
- depths of 40m (5atm) oxygen pp is roughly equivalent to breathing 100% O2 at sea level
- short term = OK
- -long term = respiratory tract damage & CNS problems
- problems linked to increased levels of free radicals
Oxygen toxicity breathing air at 90m (10atm) can lead to
seizures and coma
oxygen toxicity solution:
reduce the oxygen concentration in the mixture
decompression sickness:
build up of N2 in tissues with time at depth
- if return to sea level too quickly this gas comes out of solution and forms bubbles
- overcome by slow return to normal pressures
types of decompression sickness:
two main classes:
- Type 1 DCS: linked to pains produced by bubbles forming in muscles and joints
- Type 2 DCS: more serious: bubbles in CNS, lungs and CVS
