PHYSICAL AND COGNITIVE SYMPTOMS ASSOCIATED
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PHYSICAL AND COGNITIVE SYMPTOMS ASSOCIATED WITH ALMOST LOSS OF CONSCIOUSNESS (ALOC) PowerPoint PPT Presentation


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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

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PHYSICAL AND COGNITIVE SYMPTOMS ASSOCIATED WITH ALMOST LOSS OF CONSCIOUSNESS (ALOC)

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Physical and cognitive symptoms associated with almost loss of consciousness aloc

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


Physical and cognitive symptoms associated with almost loss of consciousness aloc

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

GLOC

ALOC?

Blackout

Light Loss

Normal

Spectrum of Consciousness


Physical and cognitive symptoms associated with almost loss of consciousness aloc

Dynamic Flight Simulator, Warminster, PA


Physical and cognitive symptoms associated with almost loss of consciousness aloc

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 in0.25 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 lastnumber after run when vision recovers


Physical and cognitive symptoms associated with almost loss of consciousness aloc

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


Physical and cognitive symptoms associated with almost loss of consciousness aloc

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:

    • Solid state laser diodes (GaAlAs) emittingpulsed light at 780 nm (Hb) and 880 nm (HbO2)

  • Detectors:

    • Asymmetrically arranged to allow for

    • measurements at different tissue depths


Physical and cognitive symptoms associated with almost loss of consciousness aloc

+Gz onset

rSO2max

rSO2zero

rSO2min

rSO2 Parameters

1.A 60 second average preceding the onset of each pulse was calculated and served as the baseline (rSO2base);

2.Time from +Gz onset to the minimum rSO2 (Tmin) and the difference between rSO2base and minimum rSO2 (rSO2min);

3.Time from rSO2min to maximum rSO2 (rSO2max) during recovery (Tmax) and the difference between rSO2min & rSO2max;

4.The total time (Ttotal) from +Gz onset until rSO2 returned to a value of zero after the run (rSO2zero);

5.The rate of change (slope) from +Gz onset to rSO2min;

6.The rate of change from rSO2min to rSO2max;

7.The rate of change from rSO2max to rSO2zero;

8.The time from rSO2min to rSO2zero;

9. The time from rSO2max to rSO2zero.

NIRS Analysis: Relative change O2 content ( rSO2 )


Physical and cognitive symptoms associated with almost loss of consciousness aloc

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

+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


Physical and cognitive symptoms associated with almost loss of consciousness aloc

Category

Physical

Cognitive Deficits

Emotional

Symptom

Tingling in hands, arms, & face

Dazed or blank facial expression

Twitching in arms & hands

Eye movements

Whole body shaking

Facial relaxation

Overall loss of control

Hearing loss

Transient Paralysis

Confusion

Amnesia

Delayed recovery

Difficulty in forming words

Disorientation

Pleasant feelings

Concern

Surprise

Unpleasant feelings

# Episodes

40

27

20

18

16

10

10

8

6

34

22

18

8

7

13

7

5

4

# Subjectsw/symptom

7

8

8

5

4

5

5

4

4

9

7

7

3

6

7

6

3

2

# Repetitions

of symptom

6

6

5

3

2

2

3

2

2

9

6

5

2

1

4

1

2

2

Most Prevalent ALOC Signs & Symptoms


Physical and cognitive symptoms associated with almost loss of consciousness aloc

# Subjects

3

3

4

2

4

3

3

3

3

5

# Repetitions

2

1

1

2

3

1

2

0

1

3

with symptom

of symptom

Altered States of Awareness

Unusual perceptions & LOC experiences

Symptom

Thought that they had experienced ALOC

Thought that they had experienced GLOC

Unsure if they experienced GLOC

Knew they had not experienced GLOC

Floating Sensation

Fuzzy Headed

Light Feeling or Suspended Sensation

Lightheaded

Mumbles or Speaks During Light Loss

Vacant Feeling (“Numbness of the Brain”

or a “Frozen Moment in Time”)

# Episodes

9

5

5

5

15

5

5

3

5

12


Physical and cognitive symptoms associated with almost loss of consciousness aloc

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+8 Gz+10 Gz

Correct

4.45 ± 1.19

Incorrect

4.70 ± 1.08

Correct

2.46 ± 0.68

Incorrect

2.89 ± 0.62

Correct

2.22 ± 0.26

Incorrect

2.81 ± 0.09

  • Incorrect responses may indicate amnesia

Point at which number

incorrectly recalled

Before the pulse began

During G onset

During G plateau

Recalled number

not in sequence

* Recalled number not in

sequence off by 1 digit

Total # subjects

with incorrect recall

8

3

3

7

6

Total #

incidents

14

3

3

8

6

Incidents

at +6Gz

3

1

3

4 ( 3*)

3

Incidents

at +8Gz

8

1

-

4 ( 3*)

3

Incidents

at +10Gz

3

1

-

-

-


Physical and cognitive symptoms associated with almost loss of consciousness aloc

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 rSO2min to rSO2zero longer during ALOC compared toasymptomatic 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


Physical and cognitive symptoms associated with almost loss of consciousness aloc

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.)


Physical and cognitive symptoms associated with almost loss of consciousness aloc

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.


Physical and cognitive symptoms associated with almost loss of consciousness aloc

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 tocause the resultant changes in behavior, perception andcognition.


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