Noninvasive Monitoring of Human Consciousness by Near-Infrared Spectroscopy (NIRS) during High Gz Stress

1
Noninvasive Monitoring of Human Consciousness by
Near-Infrared Spectroscopy (NIRS) during High
Gz Stress
April 13, 2002

• Han C. Ryoo, Ph.D.
• Hun H. Sun, Ph.D.
• Barry S. Shender, Ph.D.
• Leonid Hrebien, Ph.D.
• Department of Electrical and Computer
  Engineering
• School of Biomedical Engineering, Science and
  Health Systems
• Drexel University, Philadelphia PA. 19104
• Naval Air Systems Command, Crew Systems
  Department
• Patuxent River, MD 20670

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Objective
1

• Study Correlation between Oxygen Saturation
• and Human Consciousness under high Gz
  stress

3
Experimental Protocol
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• Acceleration (Gz) stress profiles for human
  centrifuge
• A) Sustained high Gz Stress From a rest
  plateau of 1.25 Gz, the centrifuge will
  accelerate to a peak Gz of 6, 8 or 10 in 1.25
  seconds and maintain the peak until either G-LOC
  occurs or 15 seconds has elapsed.
• G-LOC Gz Induced Loss of Consciousness
  (LOC), A-LOC Almost LOC
• B) Multiple high Gz Pulses A series of runs
  will be conducted until G-LOC occurs. From a rest
  plateau of 1.25 Gz, the centrifuge will
  accelerate to a peak of 6, 8 or 10 in 1.25
  seconds and maintain the peak for 0.5 seconds.
• If G-LOC does not occur, the time at peak
  will be extended in 0.25 second increments until
  G-LOC occurs.
• - Resting period of 3 minutes between pulses

0.25
0.5
0.75
1.0 seconds
G-LOC or 15 Sec
..
6, 8, 10 Gz
(A)
(B)
3 mins
4
Relative Oxygen Saturation (rSO2) vs. Gz Stress
Sustained Gz
Pulse Gz
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Experimental Setup for Near-Infrared Spectroscopy
(NIRS)
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• Two GaAlAs Laser Diodes 810, 840 nm, lt 100
  mW/cm2
• One Photodetector 4.4 cm away

Laser Diode
Photodetector
Brain
Modified Beer-Lambert Law
OD log10(Ii/It)eCD DPF G
OD optical density, Ii and It light intensity
incident and transmitted e extinction
coefficient, G Geometric factor DPF
Differential pathlength factor, C Concentration
of hemoglobin, D distance between sensors
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Theoretical Analysis and Computational Basis
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• mal1 eHbl1Hb eHbO2l1HbO2, where mal is
  absorption coefficient (cm-1)
• mal2 eHbl2Hb eHbO2l2HbO2 at
  wavelength l

DHbHb(transient)-Hb(Baseline)
(eHbO2l1D mal2- eHbO2l2D mal1)/ (eHbl2eHbO2l1 -
eHbl1eHbO2l2) DHbO2HbO2 (transient) - HbO2
(Baseline) (eHbl2D mal1- eHbl1D mal2)/
(eHbl2eHbO2l1 - eHbl1eHbO2l2)
DODl ODl (transient) ODl (Baseline)
D mal (D DPFl ) where D mal elCl
(transient) Cl (baseline) Then finally,
D mal DODl/ (D DPFl )
Differential Pathlength Factor

• BV DHbO2 DHb, Change in Blood Volume
• DrSO2 DHbO2 / DBV, Regional Oxygen Saturation

(Essenpreis et al, Appl. Optics, 1993)
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Oxygen Saturation (rSO2)under Gz Stress
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8
Correlations to be Studied
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( 9 Subjects, 124 Gz exposures 13 under
sustained, 111 under pulse )
Oxygen Saturation (NIRS)
Gz Exposures 1. Sustained 2. Pulse
Compete loss of consciousness (G-LOC) Incapacitati
on Time (ICAP) Almost loss of consciousness (A-LOC
)
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Data Analysis and Discussion Pulse Runs
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1. At 6 and 8 Gz, the amount of saturation
drop during A-LOC and G-LOC is significantly
greater than normal condition 2. The level
of oxygen saturation is not significantly
different between A-LOC and G-LOC 3. At 10 Gz,
it is not clear possibly due to sensor shift
or two few data points.
Normal A-LOC G-LOC
6 Mean -3.6765 -4.6725 -5.3626
STD 1.1269 0.5947 2.0909
8 Mean -4.8740 -6.5780 -6.9621
STD 0.8953 0.8401 1.3684
10 Mean -4.4243 -5.5970 -5.6276
STD 1.4794 0.7105 1.8859
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Data Analysis and Discussion Pulse Runs
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Normal A-loc G-loc
Mean -4.3392 -5.3705 -5.9841
STD 1.2569 1.1109 1.8235
I. The drops in oxygen saturation level for
both A-LOC and G-LOC is significantly greater
than under normal condition. II.Oxygen
saturation between A-LOC and G-LOC is not
significantly different
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Comparing Sustained and Pulse Gzunder G-LOC
 
 
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Oxygen Saturation (rSO) under Sustained and Pulse
Gz Stress
Incapacitation Time (ICAP) at G-LOC under
Sustained and Pulse Gz
6 8 10
Sustained rSO2 Mean -3.6216 -4.1337 -4.4467
STD 0.6443 1.4986 1.0568
ICAP Mean 14.6543 18.9450 16.7667
STD 3.0088 2.5341 4.0115
Pulse rSO2 Mean -5.3626 -6.9621 -5.6276
STD 2.0909 1.3684 1.8859
ICAP Mean 10.5940 9.6320 8.6900
STD 4.3611 2.2263 3.2348
The oxygen saturation levels and Incapacitation
time during G-LOC are not significantly different
for different Gz level
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Comparing Sustained and Pulse Gzunder G-LOC
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Effect of Gz Profile Type I. Oxygen saturation
levels (rSO2) during G-LOC are significantly
lower during repeated Gz pulse exposure than
during sustained Gz exposures II.
Incapacitation Time (ICAP) After
G-LOC, ICAP is significantly greater for
sustained Gs exposures than for repeated Gz
pulse exposures
Sustained Pulse
rSO2 Mean -3.9447 -5.9841
STD 1.0035 1.8235
ICAP Mean 16.3329 9.6387
STD 3.4342 3.2384
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Conclusion
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• The total incapacitation time after GLOC was
  dependent on the nature of the stimulus
  (sustained Gz or short duration pulse Gz)
• Oxygen saturation level may be used as a
  predictor of loss of consciousness
• Useful to design closed loop control systems for
  personal protective gear for pilots, AND/OR to
  implement automatic recovery systems to prevent
  the loss of life and aircraft after GLOC