High G physiology and protection Flashcards
what is the classification of acceleration. Short, intermediate and long
Short: impact eg crash <0.5 sec
Intermediate:ejection, catapult/cable. 0.5 - 2.0 secs
Long: linear - takeoff, radial - ACM/manoeuvring >2.0sec
Newton’s first law
Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it
Newton’s second law
the relationship between an object’s mass, it acceleration and the applied force. F=ma
Acceleration and force are vectors
Newton’s third law
For every action there is an equal and opposite reaction. eg acceleration and inertial force
Describe the G axes
\+Gz= superior to inferior -Gz= inferior to superior \+Gx=anterior to posterior -Gx=posterior to anterior \+Gy= to left -Gy=to right
G profiles of ADF aircraft
- F-35
- Hawk 127
- PC-21
- F/A 18 honet
F-35 = -3G to +9G
Hawk 127 = -4G to +8G
PC-21 = -4G to +8G
F/A 18 Hornet = -3.5G to +7.5G
Describe the Gz continuum
Weight increase Grey out black out A-LOC G-LOC
physical Effects of +Gz
Face sag increase wt - unassisted escape impossible at >3G - Can't lift head up >4G - Can't lift limbs at >8G
Cardiology effects from +Gz environment
blood pooling
reduced cerebral blood flow
Dysrhythmogenic due ot autonomic imbalance due to stretching of conduction system
Describe Grey Out
Causes tunnelling of vision
+3 to +4Gz
vision affected first due to pressure in eyes
peripheral effected first as greatest distance from optic artery.
Describe Black out
Causes complete loss of vision
+ 4 to +4.5 Gz
still conscious but no vision
How does +Gz worsen hypoxia
Changes to lung tissue
- upper alveoli are distended, lots of air
- lower alveoli are compressed, no air
Changes to blood flow
- decreased flow to upper lung
- increased flow to lower lung
exacerbates V/Q mismatching predisposing to hypoxia
Describe Oxy lung
occurs when >+3Gz, using G suit, breathing oxygen
V/Q mismatch related hypoxia reduced G performance
presents as dry cough, pain beneath the sternum, inability to take a deep breath
resolves quickly post flight with deep inspirations and/or coughing
ACBC
protective factors for Oxy lung
AGSM
pressure breathing
>40% nitrogen
incentive spirometers
MSK effects by +Gz
Short term
- acute musculo-ligamentous strains and sprains called burners and stingers
Long term: degenerative disc disease and osteoarthitis
explain G measles and G roids
G measles: petechial haemorrhages in skin, dependent areas of body
G roads: Haemorrhoids, may cause bleeding and irritation
Describe the recovery from G-LOC
absolute incapacitation 15 seconds
relative incapacitation 15 seconds
full recovery 1-5 mins
Subtle cognitive impairment up to 24hrs
describe almost loss of consciousness
G induced impairment of cerebral function with no LOC, short duration, rapid onset G exposure, typical duration approx 5 sec
Lights on but nobody home
Symptoms: - sensory disturbances - euphoria - amnesia - apathy - loss of short term memory - word forming difficulty - reduced auditory acuity - motor disturbances similar to the relative incapacitation stage of G-LOC
what is symptoms during recovery from G-LOC
Euphoria/dreamlike state confused and disorientated muscle spasms/seizures light-headedness Amnesia in 50% of cases psychological suppression/denial
Factors that increase risk of G-LOC
Unprepared for G U/S anti-G suit Rapid onset of G lack of experience layoff minor illness missed meal hangover unfit
Immediate actions after G-LOC event
Declare PAN fly straight and level to regain capability Simple approach and landing review by AVMO to ID Risk factors ASOR Return to flying next day
Clinical management of G-LOC
Medical history sortie profile 72hr history of the crew IX predisposing Risk Factors Manage as appropriate TMUFF 24 hours - can fly the next day
what physiological factors might effect G tolerance
Illness medications/supplements hypoxia/hyperventilation heat stress dehydration alcohol
Pilot fitness checklist
IM SAFE illness medication stress alcohol fatigue emotion
what personal factors affect G tolerance
Unprepared lack of experience previous lay-off missed meal fatigue
What sortie-related factors affect G tolerance
Sortie-related Peak G level G onset rate push pull effect poor AGSM
How do Baroreflex response to falling BP
baroreceptors inhibited decreased impulses to the brain decreased PNS active and Increase SNS Effects - Heart: increase HR & contractility - Vessels increase vasoconstriction - Adrenal gland: release of adrenaline and noradrenaline.
results in increase contractility and vasoconstriction = increase BP
take 6-12 secs to work
effects of negative G
defined as less then +1Gz manouevre
poorly tolerated
Head level BP increase
LOC from - 4Gz
Explain what happens during -Gz
baroreflexes in reverse
- hydrostatic effects cause stretch which results in heart slows, blood vessels dilate, BP falls
Symptoms: facial pain/fullness, eye discomfort, nose bleeds, red out, headaches, mental confusion, unconscious -4Gz
Explain the push - pull effect
when performing <1+Gz manoeuvre which triggers baroreflexes to drop blood pressure. then moving to >1+Gz which drops the BP due shift of hydrostatic pressure prior to the baroreflexes being able to increase BP. Results in GLOC earlier then expected
what High G defence training strategy
education about High G physiology AGSM Anti G garments physical conditioning centrifuge training
Steps to prevent neck pain
Before flight
- fitness and training
- core upper body strength. neck, generic isometric or physio specific.
- pre-flight stretch and warm up
Inflight
- pre -positioning
- plan head movements
- use of structures
post-flight
- stretch and cool down
symptoms management
- stop flying
- early self tx
- rest, stretch +/- analgesia
- if no improvement seek AVMO &/or physio early.
What is the most effective method to prevent G-LOC
anti-G straining manoeuvre
Describe AGSM and how much tolerance does it give
Adds +3 to 4 Gz tolerance
2 parts
- Continuous muscle contraction started prior to onset of G force. Contract legs, buttocks, abdominals.
- Breathing: increase intrathorac pressure which increases cerebral circulation. breath every 3 secs to allow heart to refil.
Common mistake with AGSM
failure to anticipate G Inadequate strain poorly coordinated strain Failure to maintain AGSM during G offset Breathing cadence Fatigue due to poor energy conservation
How much protection does anti G suit give against G
Adds 1-1.5 G tolerance
makes AGSM easier
extended coverage adds 2-2.5 G tolerance
how much protection does positive pressure breathing for G and what are the problems
PBG at 30mmHg fives +3Gz of protection.
problems
- doesn’t protect against against rapid G onset
- communication issues
- mask seal problems
- high G forearm pain
- decrease venous return
The most effective form of G protection is provided by A the pneumatic anti-G suit B the AGSM C positive pressure breathing D reclined seating
B the AGSM
