Han C. Ryoo # , Ph.D. Hun H. Sun # , Ph.D. Barry S. Shender, Ph.D. Leonid Hrebien + , Ph.D.

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

2. 1 Objective Study Correlation between Oxygen Saturation and Human Consciousness under high +Gz stress

3. 2 Experimental Protocol • 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

5. 3 Experimental Setup for Near-Infrared Spectroscopy (NIRS) • Two GaAlAs Laser Diodes : 810, 840 nm, < 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

6. mal1= eHbl1Hb +eHbO2l1HbO2, where mal is absorption coefficient (cm-1) mal2= eHbl2Hb +eHbO2l2HbO2 at wavelength l 4 Theoretical Analysis and Computational Basis DHb=Hb(transient)-Hb(Baseline) = (eHbO2l1D mal2- eHbO2l2D mal1)/ (eHbl2eHbO2l1 - eHbl1eHbO2l2) DHbO2=HbO2 (transient) - HbO2 (Baseline) = (eHbl2D mal1- eHbl1D mal2)/ (eHbl2eHbO2l1 - eHbl1eHbO2l2) DODl= ODl (transient) – ODl (Baseline) = D mal (D * DPFl ) where D mal = el[Cl(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)

7. 5 Oxygen Saturation (rSO2)under +Gz Stress

8. +Gz Profiles Sustained Pulse +Gz Level G-LOC A-LOC G-LOC 6 7 20 5 8 4 11 4 10 3 3 5 Total 13 34 14 6 Correlations to be Studied ( 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) Incapacitation Time (ICAP) Almost loss of consciousness (A-LOC)

9. +Gz Level Normal vs A-LOC Normal vs G-LOC A-LOC vs G-LOC +6 t-value 3.5129 2.5349 1.3454 Two-tailed N A N G A = G One-tailed N > A N > G A G +8 t-value 5.2916 4.3049 0.6986 Two-tailed N A N G A = G One-tailed N > A N > G A G +10 t-value 1.3280 1.5334 0.0263 Two-tailed N = A N = G A = G One-tailed N A N G A G 7 Data Analysis and Discussion – Pulse Runs 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.

10. +Gz Level Normal vs A-LOC Normal vs G-LOC A-LOC vs G-LOC +6, +8 and +10 t-value 4.0054 4.1462 1.4526 Two-tailed N A N G A = G One-tailed N > A N > G A G 8 Data Analysis and Discussion – Pulse Runs 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

11. +Gz Profile +Gz Profile +6 vs +8 +6 vs +8 +6 vs +10 +6 vs +10 +8 vs +10 +8 vs +10 Sustained t-value -2.3946 -0.9309 0.8894 Sustained t-value 0.8070 1.5560 0.3059 Two-tailed µ6 µ8 µ6 = µ10 µ8 = µ10 Two-tailed µ6 = µ8 µ6 = µ10 µ8 = µ10 One-tailed µ6 µ8 µ6 µ10 µ8 µ10 One-tailed µ6 µ8 µ6 µ10 µ8 µ10 Pulses t-value 0.4393 0.7841 0.5364 Pulses t-value 1.4382 0.2104 -1.2807 Two-tailed µ6 = µ8 µ6 = µ10 µ8 = µ10 Two-tailed µ6 = µ8 µ6 = µ10 µ8 = µ10 One-tailed µ6 µ8 µ6 µ10 µ8 µ10 One-tailed µ6 µ8 µ6 µ10 µ8 µ10 9 Comparing Sustained and Pulse +Gzunder G-LOC Oxygen Saturation (rSO) under Sustained and Pulse +Gz Stress Incapacitation Time (ICAP) at G-LOC under Sustained and Pulse +Gz The oxygen saturation levels and Incapacitation time during G-LOC are not significantly different for different +Gz level

12. + Gz Level Test Result rSO2 ICAP +6, +8 and +10 t-value 3.6924 5.4029 Two-tailed SGLOC MGLOC SGLOC MGLOC One-tailed SGLOC > MGLOC SGLOC > MGLOC 10 Comparing Sustained and Pulse +Gzunder G-LOC 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

13. 11 Conclusion • 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