Lecture 2: High G effects Flashcards
which system is most (vulnerable) effected by high gravity
circulatory system
normal mean arteriole blood pressure =
90mmHg
body orientation & rate of change of acceleration determine _____ in regards to G
how much can be tolerated
At 5G foot arterial pressure is __ when standing
450mmHG
at 5G foot arteriole pressure is ___ WHEN SEATED
300mmHg
arteries and veins will _____ in response to increased pressure and large proportion of blood from ____ body is translocated to the ___ body and there is ___ cardiac output as ____
DILATE
UPPER –> LOWER
LOWER as nothing is availble to pump
accelerations of greater than 4-6 G applied in standing or seated position cause
Blackout of vision in several seconds and unconsciousness shortly afterwards
the human body has adapted to a ___ life in which we are always exposed to the gravitational force of earth =
TERRESTRIAL
- g = 9.81m/s^2
a person who weighs 70kg at 1G(earth) will actually weigh ___kg at 3G
210
if a spacecraft is travelling towards the earth and exerting thrust in that path of motion, it is accelerating at that rate PLUS
1G (9.81m/s^2)
so if you travel at 9.81m/^s you’d be weightless
even at 1G, blood pressure in an upright person is highest in
the lower extremities (the legs) and lowest in the cranium due to the HYDROSTATIC effects of gravity
our bodies have adapted to 1G environment: we have built in mechanisms to compensate for this discrepancy for example
greater vascular tone in lower limbs = blood vessels in lower limbs contract slightly to much blood back but up
at large positive G forces ____ is magnified and results in
vascular tone in lower limbs is magnified, larger discrepancy of blood pressures between cranium and the lower body occurs
-eventually results in intracranial perfusion cannot be maintained & significant cerebral hypoxia follows, result = unconsciousness
hypoxia
no blood = no oxygen
standing up quickly, increase in positive G =
- stroke volume increases
- heart rate increases
- vascular tone increases
- -> reflex, slower as u get older
what is G-LOC
G-induced loss of consciousness, –> hypoxia -> loss of consciousness, serious problem that kills a few military pilots each year
increased G and lungs
disrupt respiration by shifting blood to lungs base, collapsing the alveoli and creates a general ventilation/perfusion mismatch as air remains in the upper lung where there is little blood flow (take deeper breaths to counterbalance this, if not hypoxia - as blood reaching brain has little O2)
Geasles (G-Measles) =
occurs in gravity-dependent areas of the body where blood forced into capillaries so hard that some rupture, resulting in petechiae
other less serious effect son large G forces =
musculoskeletal pain (usually confined to the back and neck) & Geasles
what happens in G-loc
Initial symptoms
- visual = the retina is v sensitive to hypoxia, results in tunnel vision due to lack of O2.
- -visual symptoms in response progresses from increasing tunnel vision to ‘greying’ our to full ‘black out’, person retains consciousness but full retina schema causes absolute blindness
final phase as result of high G = and number of phases it entails
G-LOC
– 2 (absolute and relative phase)
G-LOC absolute phase
absolute incapacitation is the period of time when the aircrew member is physically unconscious
G-LOC relative phase
Relative incapacitation is the period in which the consciousness has been regained, butthe person is confused and remains unable to perform simple tasks (obviously cannot fly an aircraft). This period averages about 15 seconds.
G-LOC upon regaining cerebral blood flow…
the G-LOC victim usually experiences myoclonic convulsions (a seizure-like episode) and often full amnesia of the event is experience
the brain is highly sensitive to _____ and rapid loss of function follows
cellula hypoxia (lack of oxygen / blood)
After cessation of cranium blood flow reserve time of ___ seconds exists before total loss of function
4-6 seconds
to help reduce cellular hypoxia the bodies cardiac output and blood pressure ____
heart rate, stroke volume and blood pressure increases! to try and get blood to brain but takes 6-9 seconds for the reflex to initiate
positive G blood is pushed towards
FEET
negative G blood is pushed towards
HEAD
Negative G: bodies cardiac and bp response
cardiac output/SV and hence blood pressure decreasing to eliminate the excessive blood in the brain. This reflex happens much quicker (2-4 seconds)
reflex for negative G / positive G quicker?
negative (2-4s)
positive (6-9s)
does the rate at which you’re exposed to high/low G’s effect the bodies response?
YES, slower G-onset allow for increase cardiac compensation reflexes
negative G’s followed by positive G’s will place astronauts at ____ for G-LOC
VERY HIGH RISK, reflexes can’t cope with rapid changes, called the Push-Pull Effect
G-tolerance is influenced by
- heart to brain (vertical distance),
- muscle strength
- rate of G onset
- anti-G suit effectiveness
- & positioning
is their a difference in G-tolerance between males and females
NO
decrease heart to brain distance
-tilting them back, shorter person will have higher G tolerance than taller
the G-suit
- essentially like a big bladder
- plugged into aircraft console, when G-forces mount as consequences of flight inputs from pilots, a pump inflates the suit and squeezes the lower extremities and forces blood up to hypoxia sensitive organs
old G suit vs new G suit
OLD G-suit thought to provide 1 to 1.5 G protection.
NEW full body Advanced Tactical Anti-G Suit (ATAGS) reports increases
G-tolerance by a further 0.5-1 G.
And makes them less fatigue
The Anti-G Straining Manoeuvre (AGSM)
- increases aortic blood pressure
- well trained AGSM can increase G tolerance by 3 G’s
- two components
two components of AGSM (Anti-G straining manoeuvre)
Breathing: Rapid exhalation/inspiration cycles ever 3/4 seconds. maintains oxygen content & decreases CO2 in blood, while also relieving increased pressure in chest & allows heart to refill of blood
Isometric Contraction:
Flexion of skeletal muscles of legs and abdomen. Increases pressure in chest & displaces blood away from these contracted muscles into the arms chest and brain
the Anti-G Straining Manoeuvre must be an ____ habit
instinctive habit, requiring no conscious thought by professional fighter pilots
