Lecture 2: High G effects

Question 1

which system is most (vulnerable) effected by high gravity

Answer 1

circulatory system

Question 2

normal mean arteriole blood pressure =

Answer 2

90mmHg

Question 3

body orientation & rate of change of acceleration determine _____ in regards to G

Answer 3

how much can be tolerated

Question 4

At 5G foot arterial pressure is __ when standing

Answer 4

450mmHG

Question 5

at 5G foot arteriole pressure is ___ WHEN SEATED

Answer 5

300mmHg

Question 6

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 ____

Answer 6

DILATE
UPPER –> LOWER
LOWER as nothing is availble to pump

Question 7

accelerations of greater than 4-6 G applied in standing or seated position cause

Answer 7

Blackout of vision in several seconds and unconsciousness shortly afterwards

Question 8

the human body has adapted to a ___ life in which we are always exposed to the gravitational force of earth =

Answer 8

TERRESTRIAL

- g = 9.81m/s^2

Question 9

a person who weighs 70kg at 1G(earth) will actually weigh ___kg at 3G

Answer 9

210

Question 10

if a spacecraft is travelling towards the earth and exerting thrust in that path of motion, it is accelerating at that rate PLUS

Answer 10

1G (9.81m/s^2)

so if you travel at 9.81m/^s you’d be weightless

Question 11

even at 1G, blood pressure in an upright person is highest in

Answer 11

the lower extremities (the legs) and lowest in the cranium due to the HYDROSTATIC effects of gravity

Question 12

our bodies have adapted to 1G environment: we have built in mechanisms to compensate for this discrepancy for example

Answer 12

greater vascular tone in lower limbs = blood vessels in lower limbs contract slightly to much blood back but up

Question 13

at large positive G forces ____ is magnified and results in

Answer 13

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

Question 14

hypoxia

Answer 14

no blood = no oxygen

Question 15

standing up quickly, increase in positive G =

Answer 15

• stroke volume increases
• heart rate increases
• vascular tone increases
• -> reflex, slower as u get older

Question 16

what is G-LOC

Answer 16

G-induced loss of consciousness, –> hypoxia -> loss of consciousness, serious problem that kills a few military pilots each year

Question 17

increased G and lungs

Answer 17

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)

Question 18

Geasles (G-Measles) =

Answer 18

occurs in gravity-dependent areas of the body where blood forced into capillaries so hard that some rupture, resulting in petechiae

Question 19

other less serious effect son large G forces =

Answer 19

musculoskeletal pain (usually confined to the back and neck) & Geasles

Question 20

what happens in G-loc

Answer 20

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

Question 21

final phase as result of high G = and number of phases it entails

Answer 21

G-LOC

– 2 (absolute and relative phase)

Question 22

G-LOC absolute phase

Answer 22

absolute incapacitation is the period of time when the aircrew member is physically unconscious

Question 23

G-LOC relative phase

Answer 23

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.

Question 24

G-LOC upon regaining cerebral blood flow…

Answer 24

the G-LOC victim usually experiences myoclonic convulsions (a seizure-like episode) and often full amnesia of the event is experience

Question 25

the brain is highly sensitive to _____ and rapid loss of function follows

Answer 25

cellula hypoxia (lack of oxygen / blood)

Question 26

After cessation of cranium blood flow reserve time of ___ seconds exists before total loss of function

Answer 26

4-6 seconds

Question 27

to help reduce cellular hypoxia the bodies cardiac output and blood pressure ____

Answer 27

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

Question 28

positive G blood is pushed towards

Answer 28

FEET

Question 29

negative G blood is pushed towards

Answer 29

HEAD

Question 30

Negative G: bodies cardiac and bp response

Answer 30

cardiac output/SV and hence blood pressure decreasing to eliminate the excessive blood in the brain. This reflex happens much quicker (2-4 seconds)

Question 31

reflex for negative G / positive G quicker?

Answer 31

negative (2-4s)

positive (6-9s)

Question 32

does the rate at which you’re exposed to high/low G’s effect the bodies response?

Answer 32

YES, slower G-onset allow for increase cardiac compensation reflexes

Question 33

negative G’s followed by positive G’s will place astronauts at ____ for G-LOC

Answer 33

VERY HIGH RISK, reflexes can’t cope with rapid changes, called the Push-Pull Effect

Question 34

G-tolerance is influenced by

Answer 34

• heart to brain (vertical distance),
• muscle strength
• rate of G onset
• anti-G suit effectiveness
• & positioning

Question 35

is their a difference in G-tolerance between males and females

Answer 35

NO

Question 36

decrease heart to brain distance

Answer 36

-tilting them back, shorter person will have higher G tolerance than taller

Question 37

the G-suit

Answer 37

• 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

Question 38

old G suit vs new G suit

Answer 38

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

Question 39

The Anti-G Straining Manoeuvre (AGSM)

Answer 39

• increases aortic blood pressure
• well trained AGSM can increase G tolerance by 3 G’s
• two components

Question 40

two components of AGSM (Anti-G straining manoeuvre)

Answer 40

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

Question 41

the Anti-G Straining Manoeuvre must be an ____ habit

Answer 41

instinctive habit, requiring no conscious thought by professional fighter pilots