Lecture 2: High G effects Flashcards
(41 cards)
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
