Diving Flashcards
Scuba diving
Self-contained underwater breathing apparatus
Free diving
Breath-holding
Spearfishing, photography etc
Free diving mechanism
Reduced HR
Blood flow and volume is redistributed towards vital organs by means of a reflex vasoconstriction, body cooling
Risk of hypoxic blackout and drowning
Competitive apnoea
Free diving
Attempt to attain great depths, times or distances on single breaths
11 disciplines, pool (apnoea) and depth (using weights etc)
AIDA records- depth
253.2m
AIDA records- time
11 mins 35s
AIDA records- distance
30m
DAN
Annual number of breath-hold competitive and non-competitive incident cases captured from 2004 through 2013 (mean±standard deviation) was 65±18 (range 30-82).
Majority fatal incidents (2010-2013: 81% fatal)
Scuba diving buoyancy equipment
Buoyancy compensator or buoyancy control device (BCD)
Buoyancy controlled by adjusting the volume of air in the jacket
Scuba diving breathing equipment- Diving cylinders
Usually contain air (mixture 21% )2, 78% N, 1% other gases mainly argon) or pure oxygen or nitrox (mixture of O2 and air)
Regulator mechanism to control gas pressure
Submersible pressure gauges
Open circuit used more commonly (exhausts exhaled air to the environment)- exhale through mouth
What happens to vol. of gas in your lungs or BCD jacket as you descend deeper in water
It decreases (Boyle’s)
What happens to vol. of gas in lungs or BCD jacket as you descend in colder water
Drops
charles
What happens to gas pressure of cylinder when you enter into cold water?
Drops
gay loussac
Ideal gas law
Pv=nRT
Ideal gas law- what is P
Absolute pressure
Ideal gas law- what is v
Volume
Ideal gas law- what is N
Number of moles
Ideal gas law- what is R
Universal gas content
Ideal gas law- what is T
Temperature
Boyle’s law
P and V inversely related
Gay-Lussac’s law
P and T directly related
Charles law
V and T directly related
Implications of gas law in diving
Temp gets colder –> pressure of cylinder may drop + vol of air in lungs/BCD drops
As pressure increases in deeper diving, vol of air in lungs/BCD drops
More gas will diffuse into tissues as depth of diving increases
Dalton’s law
Total pressure exerted by a mixture of gases is equal to the sum of pressures that would be exerted by each of the gases if it alone were present and occupied the total volume
PTotal=Pp1+Pp2+…+Ppn
Henry’s law
The amount of any given gas that will dissolve in a liquid at a given temperature is a function of the partial pressure of the gas that is in contact with the liquid and the solubility coefficient of the gas in the particular liquid
Pressure vs depth
As depth increases, gas pressure increases
–> partial pressures of the O2 and N in the breathing air increase
As depth increases, more gas will dissolve into the blood and body tissues
For every 33 feet depth in sea water, the pressure increases by
1 bar
Nitrogen narcosis
Increased nitrogen into the blood stream can lead to a narcotic feeling at depth
How many feet is equivalent to effects of 1 alcoholic drink
Every 50ft (15m)
What can divers experience at 150ft (46m)
Alterations in reasoning, memory and response time
Idea fixation
Overconfidence
Calculation errors
Nitrogen narcosis physiology
As diver descends and pressure increases, increasing amounts of N dissolve and accumulate in lipid component of tissues
As long as pressure is maintained, regardless of quantity of gas that has dissolved in tissues, gas will remain in solution
Nitrogen narcosis ascending
When diver ascends, a lag occurs before saturated tissues start to release nitrogen back in blood
When critical amount of N is dissolved in tissues, ascending too quickly causes dissolved N to return to its gas form while still in blood or tissues, causing bubbles to form
Nitrogen narcosis bubbles
If bubbles still in tissues, can cause local problems
If in blood, embolization may result
Further reductions in pressure while flying or ascending to higher altitude also contribute to bubble formation
Diving safety
Tables/dive computers used to show relationship between given depth of water + time diver can stay down
Safety stop every 5 metres, and not to ascend at pace more than 10m/min
Safety stop every … metres
5
Don’t ascend at a pace more than
10 metres/min
DCS stands for
Decompression sickness
Type I DCS sympoms
Pain (the bends) occurs in most patients (70-85%)
Pruritus, or ‘skin bends’
Oedema
Anorexia or excessive fatigue
Type I DCS- pain- what joint is most affected
Shoulder
Type I DCS- what is pain like
Initially mild
Slowly becomes more intense
Many divers attribute early DCS symptoms to overexertion or a pulled muscle
Type II DCS Symptoms categories
Pulmonary
Circulatory
Nervous system involvement
Pain
Type II DCS- Pulmonary
Burning
Sub-sternal discomfort on inspiration
Non-productive coughing that can become paroxysmal
Severe respiratory distress (2% of all DCS and can cause death)
Type II DCS- Circulatory
Hypovolaemic shock
Type II DCS- NS involvement
Low back pain may start within few mins to hours after dive
May progress to paresis, paralysis, paraesthesia, loss of sphincter control, headaches or visual disturbances, dizziness, tunnel vision, and changes in mental status
Type II DCS- Pain
Reported in only about 30% of cases
Because of anatomic complexity of the central and peripheral NS, S+S are variable and diverse
Type II DCS Symptom onset
Usually quick
60% within 3 hours and 98% within first 24 hours
Can be delayed as long as 36 hours
Increased risk if diver went on high altitude within 24 hours of a deep dive
Arterial Gas Embolization (AGE) physiology
Pulmonary over-pressurization can cause large gas emboli to enter into the pulmonary vein + systemic circulation
gas emboli can lodge in coronary, cerebral, and other systemic arterioles
These gas bubbles continue to expand as ascending pressure increases –> increased severity in clinical signs
AGE symptoms and signs
Depend on where emboli travel
AGE- coronary artery embolization
Can lead to MI or dysrhythmia
AGE- Cerebral artery emboli
Can cause stroke or seizures
AGE symptoms occur
Within 10-20 minutes of surfacing (usually)
AGE symptoms
Multiple symptoms may be involved
Clinical features may occur suddenly or gradually
Dizziness, headache, profound anxiousness
Unresponsiveness, shock, and seizures
Death
AGE vs. Neurological DCS II
Based on suddenness of symptoms
AGE- Any type of dive can cause it, onset is immediate (<10-120 min) + neurologic deficits manifest mainly in brain
DCS- dive must be of sufficient duration to saturate tissues, onset is latent (0-36h) + neurological deficits manifest in spinal cord + brain
AGE neurological deficits manifest mainly in
Brain
DCS II neurological deficits manifest mainly in
Spinal cord and brain
Treatment of AGE + DCS II
Both require re-compression
Therefore differentiating between them not great importance
DCS management
Do not delay HBO therapy
Administer 100% oxygen
Do not put patient in Trendelenburg position
Consider IV fluids if available
Transfer to nearest ED + hyperbaric facility- try to keep all gear to use for clues as to why problems
Transfer to HBO facility even if improvements, as can relapse
If shock- resuscitation
In-water recompression not believed to be safe, but do if in remote areas without reachable HBO chamber support
Predisposing factors DCS- Diving factors
Inadequate decompression or surpassing no-decompression limits (includes increased depth + duration of dives, + repeated dives)
Inadequate surface intervals (i.e. failure to decrease accumulated N)
Failure to take recommended safety stops
Flying or going to higher altitude soon (12-24hrs) after diving
Rapid ascent can be due to panic- identify anxiety traits
Predisposing factors DCS- individual
Obesity (N is lipid soluble) Fatigue Age Poor physical condition Dehydration Illness affecting lung or circulatory efficiency Prior musculoskeletal injury Smoking
Dehydration
Study found significant decrease in venous bubble formation with pre-dive hydration
Illness affecting lung or circulatory efficiency
Patent foramen ovale
Prior musculoskeletal injury
Scar tissue decreases diffusion
Predisposing factors DCS- environmental factors
Cold water
Heavy work
Rough sea conditions or poor buoyancy
Heating diving suits
Cold water
Vasoconstriction decreases nitrogen offloading
Heavy work
Vacuum effect in which tendon use causes gas pockets
Heated diving suits
Leads to dehydration
Cylinders- Air
21% O2 78% N 1% other traces, mainly argon Safety depth limit about 40m Max operating depth is 66.2m
Cylinders- pure O2
Mainly used to speed the shallow decompression stops (military + commercial dives)
Only safe down to depth of 6m before O2 toxicity sets in
Cylinders- nitrox
Mixture of O2 and air
Can be used to accelerate in-water decompression stops or decrease risk of decompression sickness
Has shallower max operating depth than air
Oxygen toxicity
Harmful effects of breathing molecular O2 at elevated pressures
O2 toxicity symptoms
Disorientation Seizures Breathing problems Vision changes (retinal detachment) Death
O2 toxicity pathophysiology
Collapse of alveoli in lungs Hypoxia Destruction of cell membrane which can lead to chemical toxicity and haemolysis Hepatic + retinal damage Neural toxicity
Ear barotrauma
Can affect external, middle or inner ear
Middle ear barotrauma
Most common being experienced between 10-30% of divers
Due to insufficient equilibration of middle ear
External ear barotrauma
May occur on ascent if high pressure air is trapped in external auditory canal either by tight fitting diving equipment or ear wax
Inner ear barotraums
Less common
Can lead to varying degrees of conductive and sensori-neural hearing loss as well as vertigo and auditory hypersensitivity
Pulmonary barotrauma
Usually caused by breath holding on ascent
Compressed gas in lungs expands as ambient pressure decreases, causing lungs to over expand and rupture unless diver breathes out
No associated pain
Buoyancy
An object, wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object
Maintaining neutral buoyancy is key to easy diving
Adjust buoyancy before dive
Weights
wetsuit
water temp
Adjust buoyancy during dive
BCD
Exhale/inhale
Swimming position
Too buoyant
Harder work to stay done
can’t do safety stop on ascent
Too heavy
Difficult adjusting buoyancy at different depths
Constantly having to add or remove air using BCD
Divers Alert Network
169 deaths involving recreational scuba diving during 2016
Diving fatalities are a global hazard, occurring in tropical seas and colder waters alike.
In 2016, 4 out of 5 decedents were male-similar to previous years
In 2016 the leading cause of death was drowning, and the leading disabling injury that led to death was cardiovascular-related problems
Mortality and morbidity
Fewer than 1% of divers experience DCS
Most common cause of dive-related death is drowning (80%)
Asphyxia (due to entrapment and insufficient gases): common cause of death
AGE death causes
Overwhelmingly caused by emergency assent with insufficient gases as key contributing factor
For those older than 40, association with CV disease
AGE- HBO treatment
Mortality + morbidity directly related to HBO treatment
If recompression within HBO occurs within 5 mins, death rate 5% with little residual morbidity in survivors
If delayed 5 hours, mortality increases o 10% with residual symptoms in half the survivors
How many deaths
Fewer than 2 deaths per million recreational scuba divers
Absolute contraindictions
Epilepsy controlled by medication
Unexplained syncopal episodes
Stroke and TIA
Intracranial aneurysm, arterial-venous malformation or tumour
Progressive neurological problems- severe MS, Parkinson’s, MND
Severe heart disease
Post coronary bypass surgery with violation of pleural spaces
Lung problems
Blood disorders
Pregnancy
Severe mental health problems + drug abuse
Inability to equalize pressure in middle ear by auto-inflation or acute perforation of the tympanic membrane
Severe heart disease
Congenital heart defects
Severe valve problems
Severe ischaemic heart disease especially when not fully controlled
Post MI with LV dysfunction
Congestive HF
Dependence on medication to control dysrhythmias
Lung problems
Bullae (large air sacs) Severe asthma Chronic obstructive pulmonary disease Certain types of lung surgery Past history of spontaneous pneumothorax
Blood disorders
Severe bleeding disorders e.g. haemophilia
Blood cancers e.g. leukaemia
Temporary contraindications
Any illness requiring drug treatment may constitute a temporary disqualification if either the illness or drug may compromise diving safety
Sedatives, tranquilisers, antidepressants, antihistamines, steroids
Saturation diving
Diving technique that allows divers to reduce risk of decompression sickness (the bends) when work at great depth for long periods of time
Divers live in pressurized environment
May be maintained for up to several weeks
Diver’s tissues absorb max partial pressure of breathing gas possible for that depth + decompressed to surface pressure only once, at end of their tour of duty
Limit no. of decompressions, so risk of decompression sickness v reduced
Saturation diving record
Scientific dive in 1992
701m
43 days
Saturation diving risk
Exposure to high pressure can have negative effects on NS and risk of osteonecrosis
Atmospheric diving suit
Maintains internal pressure 1 atmosphere
Used for v deep dives up to 700m for many hours
Eliminates majority of physiological disorders associated with deep diving
Divers don’t need to decompress, no need for special gas mixtures, no danger decompression sickness or nitrogen narcosis
ADS used by US navy since
2006
