Transcript Document

PHYSICAL AND COGNITIVE SYMPTOMS ASSOCIATED
WITH ALMOST LOSS OF CONSCIOUSNESS (ALOC)
Barry S. Shender, Ph. D.1, Estrella M. Forster, Ph.D.1
Joseph P. Cammarota, Jr., Ph.D.2
Leonid Hrebien, Ph.D.3, Han Chool Ryoo, Ph.D.3
1
US Naval Air Systems Command
Crew Systems Department, Patuxent River, MD, USA
2 EDO M-Tech, Huntingdon Valley, PA, USA
3 Drexel University, Philadelphia, PA, USA
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Purpose
• Describe ALOC cognitive / motor signs & symptoms
• Classify signs & symptoms in terms of duration &
frequency of occurrence
• Determine relationship of behavioral characteristics
& available physiologic correlates
Blackout
Light Loss
Normal
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GLOC
Dynamic Flight Simulator, Warminster, PA
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Methods
• 9 relaxed unprotected subjects (1 female) with no history of previous GLOC
(Males: 31.3 ± 6.6 yr; 69.3 ± 1.9”; 173.9 ± 32.3 lb.
Female: 34 yr; 64”; 135 lb.)
• +Gz Profiles: Series of short pulses (+6, +8, +10 Gz) increasing in length in
0.25 to 1 s (depending upon light loss) increments until G-LOC
• Monitoring: ECG & Cerebral tissue oxygenation (Near Infrared Spectroscopy, NIRS)
• Subject Tasks
» Light Loss: button depressed & held from 1st occurrence until full recovery
» Math: verbal running sum until 1st occurrence of light loss, then recall last
number after run when vision recovers
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Methods
• Audio-Video analysis for candidate ALOC runs
» Digitize pre-run, +Gz pulse, & entire recovery period
» Port into PC via FireWire IEEE 1394 link
• Parameters:
» Transcript of subject and Flight Deck personnel conversation
» Light loss (LL): (i) total time from onset to full recovery,
(ii) time during post-run rest period LL persisted,
(iii) +Gz level at LL onset & offset
» Last number recalled and, if incorrect (i.e. short term amnesia), the
point when the number recalled occurred (e.g. pre-run, onset, at G)
» Determine occurrence and prevalence of physical and
cognitive / emotional symptoms
» +Gz level and duration
» GLOC recovery time
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NIRS Device
Near-infrared emitters and detectors were
embedded in an opaque neoprene pad and
positioned on the forehead.
The pad was kept in place by wrapping with coban.
(Developed by Dr. JK-J Li of Rutgers University.)
• Emitters:
•
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Solid state laser diodes (GaAlAs) emitting
pulsed light at 780 nm (Hb) and 880 nm (HbO2)
Detectors:
Asymmetrically arranged to allow for
measurements at different tissue depths
NIRS Analysis: Relative change O2 content ( rSO2 )
+Gz onset
rSO2max
rSO2zero
rSO2min
rSO2 Parameters
1.
2.
3.
4.
5.
6.
7.
8.
9.
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A 60 second average preceding the onset of each pulse was calculated and served as the baseline (rSO2base);
Time from +Gz onset to the minimum rSO2 (Tmin) and the difference between rSO2base and minimum rSO2 (rSO2min);
Time from rSO2min to maximum rSO2 (rSO2max) during recovery (Tmax) and the difference between rSO2min & rSO2max;
The total time (Ttotal) from +Gz onset until rSO2 returned to a value of zero after the run (rSO2zero);
The rate of change (slope) from +Gz onset to rSO2min;
The rate of change from rSO2min to rSO2max;
The rate of change from rSO2max to rSO2zero;
The time from rSO2min to rSO2zero;
The time from rSO2max to rSO2zero.
Results
66 ALOC episodes identified out of a total of 166 +Gz pulses:
29 at +6 Gz (7 subj.); 28 at +8 Gz (8 subj.); 9 at +10 Gz (4 subj.)
Duration (mean  standard deviation) and range of reported light loss (s) and
+Gz pulse duration (s) during 66 ALOC and 20 GLOC episodes.
Total Period of Light Loss
Persistence of Light Loss after
completion of +Gz pulse
(i.e. during rest plateau)
Length of +Gz pulse during ALOC
Length of +Gz pulse during GLOC
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+Gz level
6
8
10
6
8
10
6
8
10
6
8
10
Duration (s)
8.9 ± 3.5
7.9 ± 4.8
11.0 ± 4.4
4.7 ± 3.5
5.2 ± 4.2
8.1 ± 5.0
4.8 ± 1.1 *
2.5 ± 0.7
2.6 ± 0.4
5.7 ± 1.6
3.3 ± 0.6 +
2.9 ± 0.4
Range (s)
3.1 to 14.9
1.2 to 20.4
4.9 to 16.6
0.0 to 11.3
0.5 to 15.9
0.7 to 14.1
2.5 to 7.0
1.0 to 4.0
2.0 to 3.0
2.75 to 7.5
2.5 to 4.25
2.5 to 3.25
Most Prevalent ALOC Signs & Symptoms
Category
Physical
Cognitive Deficits
Emotional
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Symptom
# Episodes # Subjects # Repetitions
w/symptom of symptom
Tingling in hands, arms, & face
40
7
6
Dazed or blank facial expression
27
8
6
Twitching in arms & hands
20
8
5
Eye movements
18
5
3
Whole body shaking
16
4
2
Facial relaxation
10
5
2
Overall loss of control
10
5
3
Hearing loss
8
4
2
Transient Paralysis
6
4
2
Confusion
34
9
9
Amnesia
22
7
6
Delayed recovery
18
7
5
Difficulty in forming words
8
3
2
Disorientation
7
6
1
Pleasant feelings
13
7
4
Concern
7
6
1
Surprise
5
3
2
Unpleasant feelings
4
2
2
Altered States of Awareness
Unusual perceptions & LOC experiences
Symptom
# Subjects # Repetitions
with symptom of symptom
Thought that they had experienced ALOC
9
3
2
Thought that they had experienced GLOC
5
3
1
Unsure if they experienced GLOC
5
4
1
Knew they had not experienced GLOC
5
2
2
Floating Sensation
15
4
3
Fuzzy Headed
5
3
1
Light Feeling or Suspended Sensation
5
3
2
Lightheaded
3
3
0
Mumbles or Speaks During Light Loss
5
3
1
Vacant Feeling (“Numbness of the Brain”
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5
3
or a “Frozen Moment in Time”)
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# Episodes
Math Task Results
• ALOC subjects correctly recalled last number 35 times, incorrectly 31 times
• Incorrect responses often associated with longer +Gz pulse
Mean length of +Gz pulse during recall of last number of math task (sec)
+6 Gz
Correct
4.45 ± 1.19
Incorrect
4.70 ± 1.08
+8 Gz
Correct
Incorrect
2.46 ± 0.68 2.89 ± 0.62
+10 Gz
Correct
2.22 ± 0.26
Incorrect
2.81 ± 0.09
• Incorrect responses may indicate amnesia
Point at which number
Total # subjects
incorrectly recalled
with incorrect recall
Before the pulse began
8
During G onset
3
During G plateau
3
Recalled number
7
not in sequence
* Recalled number not in
6
sequence off by 1 digit
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Total # Incidents Incidents Incidents
incidents at +6Gz at +8Gz at +10Gz
14
3
8
3
3
1
1
1
3
3
8
4 ( 3*)
4 ( 3*)
6
3
3
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NIRS Results (p<0.05)
• Exposures with ALOC & GLOC compared to asymptomatic runs:
» Minimum rSO2 (rSO2min) lower
» Time to rSO2min shorter
» Total time for rSO2 to return to zero (rSO2zero) longer
» Time from maximum rSO2 (rSO2max, recovery overshoot) to zero longer
• Differences between ALOC, GLOC and asymptomatic runs:
» rSO2max greatest during GLOC, smallest during asymptomatic runs
» Rate of change between rSO2min and rSO2max fastest during GLOC,
most gradual during asymptomatic runs
• Time from rSO min to rSO zero longer during ALOC compared to
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2
asymptomatic runs
• Differences based on +Gz level:
» Tmin longer, rSO2min smaller, & slope to rSO2min longer at +6 Vs 8 or 10Gz
» rSO2max lower during +6 Vs +8 Gz
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Discussion
• ALOC is difficult to detect
» Some physical manifestations are visible
(twitching, blank expression)
» Typically need to ask subject after the run
• ALOC symptoms demonstrated in centrifuge study also
reported in survey of 70 USN & USAF aircrew
(Morrissette KL, McGowan DG. “Further support for the concept of a G-LOC
syndrome: A survey of military high-performance aviators.”
Aviat Space Environ Med 2000; 71:496-50.)
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Operational Implications
• Delay in recovery after ALOC
“It took me a while to realize what to do.”
• Disconnection between cognition and ability to act upon it
“I knew what I wanted to say but I couldn’t form the words”
• A state of confusion
“I don’t know why I’m confused” “I didn’t know what or why something was
happening”
• NIRS results
» Largest drop in rSO2 occurred during offset or into rest period
» Symptoms persist well into the period of oxygen recovery, including light
loss, confusion, tingling and involuntary movements.
» Significant increase in the reduction in rSO2 (rSO2min), greater overshoot
(rSO2max), faster change in rSO2 during +Gz-stress (Tmin2zero) and
prolonged recovery time associated with ALOC as compared to +Gz
exposures without symptoms.
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Conclusion
• ALOC is insidious and may not be recognized
» Clear description of ALOC signs and symptoms can
improve training and aircrew awareness
• It affects the CNS at a variety of levels
• ALOC may be a contributing factor in mishaps attributed
to spatial disorientation and loss of situational awareness
• In order to fully protect our aviators, it is essential to
understand how +Gz-induced changes in the CNS,
cerebrovasculature, and vestibular systems interact to
cause the resultant changes in behavior, perception and
cognition.
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