High G Physiology Flashcards
Describe flight manoeuvres that result in exposure to prolonged +Gz and -Gz acceleration
- Short duration acceleration <0.5
- Medium duration acceleration 0.5-2
- Long duration acceleration > 2.0 sec
Circular motion - centripetal acceleration causes change in direction with subjective sensation in opposite direction (centrifugal force = sensation of G)
F = mv2/r»_space; the faster you turn, the bigger the force , the tighter you turn the bigger the turn
- Air combat manoevering results in exposure in G
Explain the normal cardiovascular responses to +Gz and -G accelerations.
Acceleration creates distortion of organs and alters Q
Gz continuum: weight increase»_space; grey out»_space; black out»_space; ALOC»_space; GLOC
Blood pooling due to HSP -@ 4G, Q to Brian and eyes are diminished, venous pooling in LL and loss of central blood volume
Grey out - @3-4 G - conscious but tunnel vision
Black out - @ 4-4.5 Gz - conscious but no vision
Cardiac dysrhythmias die to stretching of heart and conducting systems
Worsening of V/Q perfusion/mismatching
What is acceleration atelactasis? How is it managed
When alveoli collapse secondary to: 1. Breathing >70% O2, 2. G suit 3. > 3G
Managed with AGSM, PPB, >40% N2 gas mix
Causes dry cough and pain behind sternum
What is ALOC
ALOC = almost LOC
G induced cerebral impairment with no LOC
Occurs with rapid onset of G exposure
About 5 seconds
Occurs @ 4.5-5G
Sx: sensory disturbances, STML, euphoria, apathy, motor disturbances
What is the GLOC sequence
- Absolute incapacitation: 15 sec
- Relative incapacitation: 15 sec
- Full recovery 1-5 minutes
- Subtle cognitive impairment for up to 24 hours
List factors that cause GLOC
List factors affecting G tolerance
Causes of GLOC:
Unprepared for G
Unsuitable G suit
Rapid G onset
Lack of experience
FActors affecting G tolerance:
Magnitude and duration of G
Rate of onset
Experience & adaptation/preparedness
Inappropriate AGSM
heat stress - for every rose in 1oC, reduces tolerance by 30-40%
Individuals - fitness, body positioning, BP
Dehydration - 2% loss in total body water ~15% reduced G tolerance
Sortie gd: peak G level, G onset rate, push-pull effect, Poor AGSM
What is negative G, when does it occur
Negative G occurs with < +1Gz manoeuvre (flying upside down, during a roll)
Head level blood pressure increases
LOC with -4Gz
Barorecpetors work in reverse with BV dilating and BP falls
What is the push pull effect
After sustaining -Gz then followed with +Gz manoever (eg rolling), baroreceptors have dilated cerebral BV then need to vasoconstrict to help maintain cerebral Q. Transient time that stimulation can’t be achieved
What is involved in AGSM
Combination of continuous contraction of abs, quads and buttocks + rhythmic breathing
Rhythmic breathing = large initial breath in then strain against glottis, quick breath out then back inq3sec
Adds on 3-4
G tolerance
Explain the physiological basis for GLOC
Due to HSP, with increasing G, there is increase pooling of blood to LL and decreased Q to cerebral vessels.
When Q to the brain ceases, patient will go into GLOC.
What are the different types and the mechanism of anti G counter measures?
Muscle tensing prevents blood from pooling into the LL and increases PR and BP
AGSM increases chest cavity pressure to assist Q to head
Anti G suits similar to muscle tensing MOA
Positive pressure breathing for G increases intrathoracic pressure; PBG @ 30mmHg gives +3G of protection at 9 G, must be used with advanced G suit
Centrifuge training : learn how to perform AGSM at different G profiles, promotes awareness of GLOC
How would you manage a GLOC incident
- Medical hx
- Sortie profile :
- flight profile leading up to incident
- anti G suit and AGSM employed
- Gz exposure during flight - 72 hour hx of crew
- Ix predisposing risk fx - usual tolerance to G,
- Manage as appropriate
- TMUFF 24hour
