REPORT NO. NADC-84021-60

FACTORS AFFECTING HUMAN TOLERANCE TOSUSTAINED ACCELERATION

Leonid Hrebien, Ph. D.Aircraft and Crew Systems Technology Directorate (Code 6061)

NAVAL AIR DEVELOPMENT CENTERWarminster, Penn;yivania 18974

andSo Edwin Hendler, Ph. D

HUMAN FACTORS APPLICATIONS, INC.295 West Street Road

Warminster, Pennsylvania 18974

30 NOVEMBER 1983 D T I "ELECTE

EB 28 8 W4

INTERIM REPORTProgram Element No. 62578N B

Approved for-Public Release; Distribution is Unlimited

CL.

Prepared ForLJ NAVAL AIR SYSTEMS COMMAND (AIR-310H)

__Department of the NavyWashington, DC 20

'S4 02, 27~ 101

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NOTICESREPORT NUMBERING SYSTEM - The numbering of technical project reports issued by the NavalS-- ,Air Development Center is arranged for specific ide&tification purposes. Each number consists of'- the Center acronym, the calendar year in which the number was assigned, the sequence number ofthe report within the specific calendar year, and the official 2-digit correspondence code of theCommand Office or the Functional Directorate responsible for the report. For example: ReportNo. NADC-78015-20 indicates the fifteenth Center report for the year 1978, and prepared by theSystems Directorate. The numerical codes are as follows:

CODE OFFICE OR DIRECTORATE00 Commander, Naval Air Development Center01 Technical Director, Naval Air Development Center•02 ComptrollerS10 Directorate Command Projects1 20 Systems Directorate30 Sensors & Avionics Technology Directorate40 Communication & Navigation Technology Directorate50 Software Computer Directorate60 Aircraft & Crew Systems Technology Directorate"70 Planning Assessment Resources80 Engineering Support Group

PRODUCT ENDORSEMENT - The discussion or instructions concerning commercial productsherein do not constitute an endorsement by the Government nor do they convey or imply thelicense or right to use such products.

APPROVED BY:

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UNCLASSIFIEDSSECURITY CLASSIVICATION Of THIS PAGE ("on Date &for**)

REPORT DOCUMENTATION PAGE BEFOR C NGFORM1. ftUPORT NUMISR L GOVT ACCESSION NO. 3. RECIPIZNT'S CATALOG NUNIER

, . NADC-84021-6o •tb, - 9)3 5.2014. TITL. (OW swua.l) 1S.- TYPC OF REPORT A PCRIOO COVERED

J Factors Affecting Human Tolerance to SustainedAcceleration _ ne__ _

SPCPERFORMING OR1. REPORT NUMIE61R

7-AIJTHR(S) 6. CONTRACT OR GRANT NUM694CO)

Leonid Brebien, Ph.D.Edwin Handler, Ph.D._:. PRFORMING -ORGANIZATIC0N NAiME ANO ACORESS I0. PROGRAM CL.MENT. PROJECT. TASK

"ARMCA & WORK UNIT NUMGERSAircraft & Crew Systems Technology Directorate7, WNaval Air Development CenPerL 62578N

S • ~~Warmin•ter, PA 18974 2S8S.... |11. CONTRIq~~.NG OFFVICE HAMS AMC ADDRELSS IL NREPORT CATS[

Naval Air Systems Co__nand 30 November 1983•4 "AIR 310H 1.• PIuM89 OF PAGES '

--( _Washinuton, DC 20360 "" - 46"14. MONITORING AGrNCY NAM& A AOORESII 0I10M•I Ave CO hII#g 0O1ff) IL SECURITY CLASS-,.C (oue WOlEI)

Unclassified

IL. OISTRI)GUTION STATEMENT (o.• Il e Rsp.t) '

'Approved for Public Release; Distribution Unlimited

17. DISTRIBUTION STATRUENT (of IN* *bufte* .meis In 88k 26, It vEtfereat bum ftopM)

IISL S4PPI.[EMNTARY MOTE.S.

11. NE. WOROG (CaslA..a mo @W aIdsooen andMitp hp Week

'PALe Seat; Acceleration Tolerance; Supination; S Pressuriza1tion

MTA (C~oatm an m9ff6eo sde Of aesueem MOd ~fr Sp Week wAmbu

Six relaxed subjects were exposed on a centrifuge to increasing G pulses in- -, order to determine their G tolerance. G protection was provided by supination

andior inflation of an.ti-G suit (ASS) bladders using a newly developed rapidresponse, servo controlled anti-O (SCAG) valve. Supination, alone or with the"ASS, was most effedtiva in increasing G tolerance. Increases- in SCA, Valveoutlet pressure were directly related to increases in G tolerance. Neither of -

two sodes of SCA' v•ave operation, ciUsed, any significant difference in S1e~ance _oio in ass•eAmmne Af comfort. When protected bv su tigagion' andDO, -, 1473 wro v *E - UNCLASSIFIED

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-,the MGS, sufficiently incriasing G ouset times reduced G tolerance. AdverseI/ co.meants: and low ratiuSs for AGS comfort followed exposure to most G pulseswhen the subjects were protected by high levels of AGS bladder pressure.p<

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INADC-84021-60

TABLE OF CONTENTS

"List of Figures ..... 2

,, List of Tables ................................................ 3

Abstract ................................................. 4

Introduction ....... .e.ee.ee.eeeeeeeeo...ee 5

Subjects ................................................ 5

SCAG Valve ................................................ 7AGV OutletrPressure ................P...................... 11Bioinstrumentation and Safety .......... ,.................. 11Procedure ...... Soo eooooo*oeoooo.oooooeoooSoSooooseooooooeoe 14Calculation of G Tolerance ................................ 14Comfort Assessment .......... 17Experimental Design oo.. . 17* Results olrne.............................................. 17

AGS Comfort Assessment ***0**** ...... ........**..*e 28

References ................................................. -44

Appendix: Definition-of Acceleration ......................... 44

p Accession-For

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By_____

Distribution/

Ava•labillt7 CodesAvail and/or

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NADC-84021-60

LIST OF FIGURES

Figure

1. Human Centrifuge of the Naval Air DevelopmentCenter's Dynamic Flight Simulator .................... 8

2. NADC curved light bar used to determine G-Toleranceby peripheral light loss ............................. 9

3. Diagram of change in body position using the PALEseat ........................................... * ..... 10

4. Modes of SCAG valve operation 12

. I- 5. Valve outlet pressure schedules used for upright andsupine body positions .... ......................... 13

6. Form used to rate AGS comfort following eachG-Tolerance threshold limit run ....................... 18

7. Components of G-Tolerance and G-Protection for variouslevels of AGS bladder inflation pressures ............ 23

8. Best fit regression lines for G-Tolerance on SCAGvalve outlet pressure gradient (psig/G) ............... 25

9. Relation G-Tolerance, G onset time, and bodyposition . . 31

10. Relative effects of AGS bladder pressure and G onsettime on adjusted comfort-scores ...................... 35

11. Mean adjusted comfort scores for AGS bladder pressurelevels and body position ............................. 37

12. Comparison for individual subjects of contributionsto G-Tolerance of AGS and supination separatelyand simultaneously combined 39

13. Diagram showing G nomenclature ......................... 45

I

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L2

NADC-84021-60

LIST OF TABLES

Table

1. Subject Characteristics ................................. 6

2. Order of Daily PLL Threshold Condition Combinations .... 15

3. Daily order of Subject Exposure Riding DFS ............. 19

4. G-Tolerance Thresholds ................................ 20

o 5. Analysis of Variance of G-Tolerance .................... 21

S6. Comparisons of G-Tolerance Differences for SCAG ValveOutlet Pressures Across All Other Independent

4, Variables ........................................... 26

7. Analysis of Variance Showing Regression of G-Toleranceon SCAG Valve Outlet Pressure ........................ 27

8. Inferences about Two Model Parameters, B and B ,for the Regression of G-Tolerance on S8 AG ValveOutlet Pressure ................... .................. 29

9. Analysis of Variance of G-Tolerance for G Onset Timeswithout AGS Bladder Inflation ........................ 30

10. Analysis of Variance of G-Tolerance for G Onset Timeswith AGS Bladder Inflation ....................... 32

11. Mean AGS Comfort Scores ................................ 33

12. Adjusted AGS Comfort Scores ............................ 34

i !13. Comparison of AGS Protection in the Upright andSupinated Body Positions 41

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NADC-84021-60

ABSTRACT Six relaxed subjects were exposed on a centrifuge toincreasing G pulses in order to determine their G tolerance. G"protection was provided by supination and/or inflation of anti-Gsuit (AGS) bladders using a newly developed rapid response, servocontrolled anti-G (SCAG) valve. Supination, alone or with the

4 AGS, was most effective in increasing G tolerance. Increases inSCAG valve outlet pressure were directly related to increases in Gtolerance. Neither of two modes of SCAG valve operation causedany significant difference in G tolerance nor in assessment-of AGScomfort. When -protected by supination and the AGS, sufficientlyincreasing G onset times reduced G tolerance. Adverse commentsand low ratings for AGS comfort followed exposure to most G pulseswhen the subjects were protected by high levels of AGS bladderpressure.

- 4

NADC-84021-60

INTRODUCTION The occasional, unexplained loss of a high-performance aircraft has given rise to speculation about the roleplayed by G-induced loss of consciousness. This speculation isnot without merit, considering that modern fighters are capable ofexposing pilots to significant G loads at rates which far exceedthose of even the recent past. While thrust-to-weight ratios ofhigh-performance aircraft have increased appreciably over the pastcouple of decades, improvements in hardware systems for protectingthe pilot against adverse G effects are only now beingimplemented. In fact, present day G-protective equipment used inmilitary aircraft is not much different from that developed during

* World War II.The most effective method of providing G protection has •been

shown to be supination of the pilot's body, so that Gz loads are7• transformed into Gx loads which are better tolerated.

Unfortunately, implementation of this technique has met withconsiderable resistance because of the drastic changes in cockpitconfiguration which would be required, including modification andrelocation of displays and controls and replacement of the presentejection seat. Partial supination, however, may be more easilyachieved, and it is likely that future high-performance aircraftwill incorporate design changes necessary for this to beaccomplished. Another way to improve G tolerance lies in theimprovement of the anti-G valve (AGV). Serious efforts are now

*. underway to modify the standard AGV in order to reduce the lagbetween G load and inflation of the anti-G suit (AGS) bladders.In addition, new AGVs have been designed which are much moreresponsive to G load, and can be made to respond to other inputs4- from the flight environment, so that anticipatory actions can betaken to provide more effective G protection. One such valve isthe servo-controlled anti-G (SCAG) valve, a prototype model ofwhich was used in the present study.

There is presently little information available on AGV outletpressures which applies to any body position other than upright.The purpose for conducting this study was to obtain data on SCAGvalve outlet pressure in the supinated and upright body positions,using G tolerance and AGS comfort as dependent variables. Inaddition, the effects of mode of SCAG valve operation andacceleration onset time were included in the experimental design.

METHOD

SubJects Before initiating-the experimental portions of thisstudy, a group of potential subjects who had been examined by aflight surgeop and found to be physically qualified were informedabout the purpose of the study and the possible hazards involved.The protocol and safety procedures to be followed were formallyreviewed and approved by the Naval Air Development Center (NADC)Committee for the Protection of Human Subjects. The informed,written consent of the six individuals who volunteered toparticipate as subjects was then obtained. Some of the physicalcharacteristics of these subjects are listed in Table 1. All ofthe subjects were naval enlisted personnel and were familiar withthe equipment to be used and the procedures to be followed.

4~5'I i1iii iIliI-l-m i |~f

NADC-84021-60

Table 1. Subject Characteristics

Sitting ShoulderSubject Sex Age Height Weight Height Height

(yr) (cm) (kg) (cm) (cm)

1 m 28 172.7 73.6 90.9 61.0*

2 M 19 182.9 84.1 94.5 63.8

3 F 21 167.6 59.1 88.1 57.6

4 14 23 190.5 93.2 98.3 69.2

5 14 23 175.3 75.0 90.9 62.8

6 14 25 172.7 68.1 90.2 59.6

*Estimated-

NADC-84021-60

Subject Prep~aration and Body Position Prior to entering theooý gondola of the NADC human centifuge, (Figure 1), ECG electrodes

were attached to the subject's torso, a remotely operated bloodpressure cuff containing ai-microphone was placed on his upper arm,and a Doppler transceiver was fixed to the skin of his foreheadoverlying a branch of the temporal artery. The subject wore shoesand socks, underwear, a flight suit, and a carefully fitted CSU-15/P AGS. After entering the gondola, the subject was restrainedby a torso harness in the Pelvis and Leg Elevating (PALE) seat andthe NADC curved light bar was positioned to encircle his head, asshown in Figure 2. The PALE seat is articulated so that itssupporting parts can be positioned from a full uprightconfiguration, similar to that, of a standard aircraft ejectionseat, to a fully reclined configuration on which the subject'sbody is completely supinated. These changes in body position are

° ' accomplished without changing the subject's eye position withrespect to his surrounding environment (Figure 3). In this study,the PALE seat was adjusted' so that the seat back assumed either a15 degree seat back angle (referred to as "upright")' or a 60degree seat back angle (referred to as "supine").G Tolerance Limit The NADC curved light bar shown in Figure 2 isoperated by the subject and provides a continuous measurement of

* his -peripheral v."'ion in the plane of the bar. During use, thesubject fixates oi, a central white light mounted on the bardirectly in front of the bridge of his nose. By exerting force ona two-axis, side arm controller with his right hand, he controlsthe lighting of any single pair of the 60 pairs of red lightI emitting diodes (LEDs) installed along the bar' at 1.5 degreeintervals. The subject is instructed to maintain a pair oflighted LEDs located at the outermost limits of his peripheralvisual field at a subjectively determined level of constantbrightness. As his visual field constricts during G, heproportionately reduces his pull on the side arm control handle.This allow's more anteriorly located pairs of LEDs to light on eachside of the central light, thereby progressively reducing theangle subtended by the lighted pairs of LEDs. If he fails at anytime to exert pull on the control handle, the pairs of illuminatedLEDs automatically converge toward the central white light at therate of 60 degrees per second. For this study, a cut-off of 60degrees on the light bar (i.e., 30 degrees on each side of thecentral light) was established as the visual angle whichautomatically stopped the centrifuge arm. The G plateau level atwhich this occurred was used, as will be described, in determiningthe subject's G tolerance limit. (The phrase "G tolerance limit"is usually shortened to "G tolerance" in this report). Thus, in

Sthe event that the subject failed to pull on the control handleduring G, when the most peripherally located pair of LEDs were

° • lit, one second' would elapse'before the centrifuge arm would beplaced in its automatic stop mode. The subjects were trained tooperate the light bar control in both the upright and supine bodypositions.SCAG Valve The bladders of the AGS were inflated with air, and'ditea, by mfea'ns of recently develop'ed SCAG valve. This valveis servo-controlled 'and depends for its action upon the ampl-ifiedvoltage difference between the output of an accelerometer, which

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NADC-84021-60

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NADC-84021-60

•:• LED

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BAR

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Figure 2. NADC curved light bar used to determine G-toleranceby peripheral light loss.

~ I 9

1iNADC-84021-60

PELVIS & LEGS ELEVATING (PALE) SEAT• I

600

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01

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* l I i Figure 3, Diagram of" change in body position using the PALE seat.

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_NADC-84021-60

senses G, and a pressure transducer, which senses the pressureinflating the AGS bladders. Amplifier gain is adjusted tomaintain maximum loop stability and minimum pressure lag. A morecomplete description of the SCAG valve and its- performance hasbeen reported (4). For this study, two modes of SCAG valveoperation were used (Figure 4). In mode I, feedback derived fromAGS inlet hose pressure controlled valve output, so that valveoutlet pressure was practically concurrent with, and directly

S- proportional to, G loading. In mode B, the initial phase of valveoutlet pressure was enhanced (simulating feedback from a pressuresensor located in the abdominal bladder of the AGS), so that valve

* outlet pressure transiently overshot the level which would havebeen provided if the valve were acting in the I mode. The neteffect of this enhancement was to decrease the lag, by severalhundred millisecon•s, between the start of G onset and thebeginning of abdominal bladder pressurization.AGV Outlet Pressure The AGV outlet pressure versus G schedule

-= ut-lized was based upon results obtained from an earlier series oftests in which the SCAG valve was used (4). In the earlier tests,Gtolerance was determined from recordings of temporal artery meanblood flow velocity, measured with a Doppler tranceiver in amanner similar to that already described in this report. The AGVschedule developed was based upon the following equations:

• P - 1.5 (G -1) Cos (0- i5) (1)

where P is the AGV outlet pressure in psig and equals 0 whenG 4 1.5, G is the resultant (1 (see Appendix A), and e is theseat back angle in degrees. When e - 15, equation (1) reduces to:

P - 1.5 (G - I) (2)

Equation (2) is the middle curve shown in the left portion ofFigure 5, and 1.50 psig/G was used in the present study as the"middle* level pressure gradient for the upright body position.Two other gradients, one 25 percent greater than, and the other 25percent less than the middle level, were also evaluated. The twocurves incorporating these gradients are also shown in the leftportion of Figure 5, the former referred to as "high* and, thelatter as 11644. For comparison, the schedule which the militaryAGV must meet is shown by the stippled area in Figure 5. Thisschedule was taken from the pertinent military specificationissued by the U.S. Department of Defense (7). Application ofequation (1) for the 60 degree seat back angle results in:

P_ 1.06 (G -1) (3)

Equation (3) is represented by the middle curve in the rightportion of Figure 5. Again, curves with 25 percent greater andlesser gradients are shown above and below the middle levelgradient curve. No official publication specifies AGV outletpressures for any body position other than upright.Bioinstrumentation and Safety Lighting in the centrifugegondola was subdued an-iZ aclosed-circuit, low light level videocamera provided continuous viewing of the subject's, head on video

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NADC-84021-60

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Figure 5. Valve outlet pressure schedules used for upright-andsupine body positions. Shaded area shows anti-GValve out-let pressures specified by MILSPEC MIL-V-93700D (AGS)..

j 13

NADC-84021-60

-•I monitors used by the centrifuge operators and project personnel.Two-way oral communication with the subject was maintainedthroughout the runs. Strip-chart recordings of applied G, meanand pulsatile blood flow velocity, displacements of the LED pairson the light bar, SCAG valve outlet pressure, electrocardiograms,and heart rate were made; this information and the verbalcommunication with the subject were also recorded on magnetictape. Intermittent blood pressure measurements were recorded on-paper tape by the medical monitor. Applied G and heart rate werepresented continuously on LED displays for viewing by projectobservers, and an audio rendition of Doppler transceiver outputwas broadcast during each acceleration run.Procedure After the subject was seated and restrained in thegondola, and the bioinstrumentation, visual light bar,communications, G-protective system, and safety systems checkedfor proper function, the gondola door was closed and thecentrifuge arm was activated. Before and after all accelerationruns, the arm continued to turn slowly, applying 1.03 G as abaseline acceleration. An initial plateau level of 2.5 G for theupright, and 3.5 G for the supine body position was selected forthe first ride for each subject. Subsequent plateau startinglevels depended upon consideration of the particular subject'spast performance.

The acceleration profiles, for each set of conditions shownin Table 2, consisted of haversine-shaped onsets-and offsets ofacceleration over time, lasting 2, 4, or 8 s, with 15 s plateausinterposed. The subject began controlling the peripheral lights15 s before the onset of the acceleration profile; a 5 s countdownpreceded the beginning of G onset. For 15 s after the completionof acceleration offset, the subject continued to control theperipheral lights. If the subject successfully tolerated theacceleration profile, the next run was made with the plateauincreased by 0.5 G. This procedure was repeated until the subjectwas unable to complete the 15 s plateau period, that is, hisvisual angle, as measured on the curved light bar, had contractedto 60 degrees (or less). The procedure of determining the Gtolerance limit was repeated three times per day per subject, eachtime with a different combination of independent variables, asshown in Table 2. Rest periods of at least 1.5 min separatedsuccessive runs. Runs were repeated in cases where subjects:inadvertently lessened their pull on the side-arm controller,thereby allowing the LED pairs to converge to the 60 degreeposition and automatically stop the run.Calculation of G tolerance The following formula was used tocalculate to'erance:

G - + 0.5 (T - 0.5To/To + 15) (4)

where,

G - G'tolerance (G)GIS - highest G plateau tolerated for 15 s (G)T -- Duration of exposure to highest G plateau from its starat -

1.03 G to PLL (peripheral light loss endpoint) (s)T o onset timeof G profile for which T wans measured (C)

NADC-84021-60

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In essence, this formula assumes a symmetrical S-shaped onset ofthe G-time profile, adds one-half of the onset G-time 'to theplateau G-time until PLIL occurs, and then uses this value todetermine the proportion of the 0.5 G step increase betweensuccessive runs to be added to the highest G plateau tolerateid-for15 s. This procedure differs slightly from that used by Crosbie(4), who utilized the complete -G-time profile, including theentire G-time onset segment, in:determing the proportion of the0.5 G step increase to be added to the highest plateau toleratedfor 15 s. Since Crosbie was concerned with only 3 s onset times,his calculated G tolerance values are 0.04 G greater than those

I calculated by using equation (1). However, for longer onsettimes, a more appreciable discrepancy would result if the entireonset time (.09 G for the 8 s onset time used in the presentstudy) were included in calculating G tolerance.Comfort Assessment The subjects were required to evaluate andreport AGS comfort following each run for which a tolerancethreshold was determined. In order to assist the subject in-rating AGS comfort, a copy of the. numerical scale and adjectiveequivalents was installed within the subject's view iniide thegondola. This scale extended linearly from 0 to 100 with thefollowing equivalents: 0, very poor; 25, -poor; 50, fair-; 75,good; 100, excellent. Following the completion of the thresholddetermining run, the subjects- made a numerical rating of AGScomfort and commented upon any particular aspects relating tocomfort which they believed to be pertinent., These reports wereentered, on the form shown as Figure 6- by the project officer.Experimental Design The overall scheme, showing the order andcondition combinations for each series of runs leading to a Gtolerance threshold determination is shown in Table 2.- A table ofrandom numbers was -used in formulating the order, in whichcondition ,combinations- were imposed. Two -to five separate runswere required per subject to arrive at the tolerance endpoint foreach combination of conditions. Each subject rode the centrifuge-once per day, in accordance with the schedule shown in Table 3.Occasional deviations fromt the scheduled -order shown in Tables 2and 3-were necessitated by events over which-the investigators had-no control.

RESULTS

G.tolerance The G -tolerance means and their standard errors-- or the group of six tubjects are given ih Table 4. An analysis

.f v.ariance-using the 0riginal d4ata (Table 5) shows the4 significant- factors to-.be BodyPosition, -Valve Outlet Pressure,_Mand G. Onset Time.

i... Body:Poiitibn: As expected, this factor had the most drastico• f effect on G tolerance. As -shown 'in -Figure 7, the mean uprighttoierance. of the group of xubjecti was increased from 3.13 + 0.104 (variation about the mean is expressed in this report asstandard: error• to 4.84 + 0.16 G when the body position was

--changed- -from upright to supine, without inflation of the AGSIbladders., ThIs change in body positions therefore resulted in aninorease -of',about 53 percent in G tolerance. When the AGS

Sbladder6 were inflated, mean G tolerance increased from- 4.30 +

-17

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NADC-84021-60

DATE

'NAM

RATE THE COMFORT OF THE ANTI-G SUIT AFTER EACH G THRESHOLD RUN.

VERY POOR FAIR GOOD EXCELLENTPOOR

FIRST-• THRESHOLD

RUN 0 25 50 75 100

COMMENTS:______________________

VERY POOR FAIR GOOD EXCELLENTPOOR

SECONDTHRESHOLDRUN 0 25 50ý 75 100

COMMNTS:

I ' o_ __ _ _ _ _ _ __- -VERY POOR FAIR GOOD EXCELLENTii, POOR

TIRUN 0 25 50 75 100I__ _____,,________________,_

- Figure 6 -Form used to rite AGS cormfort following .each G-toler-anceS~thrýeshold limi t runi.' !a

S...... NnlI I llli~ IIln ]I l l

NADC-84021-60

Table 3. Daily Order of Subject Exposure Riding DFS-

Dayl1 Day_ 2 Day DaDy5 Da_6_a

SI S5 S2 S3 S4 S6 S3

S2 S4 S3 S5 S6 Si S5

S3 $6 Sl S2 55 S4 S2

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s6 S2 S4 Sl S3 S5 S1

Day,8 Day 9 Day 10 Day ii Day 12 Day 13 Day 14

Sl S6, S4 S2 s5 S3 Sl

S2 Si S6 S3 $4 S5 S2

S3 S4 S5 Sl S6 S2 S3

S4 S3 S2 S5 Sl s6 S4

S5 S2 Si S6 S3 S4 S5

S6 5 S3 S4 S2 Si S6

19

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NADC-84021-6o

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NADC-84021-60

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NADC-84021-60

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22

NADC-84021-60

COMPONENTS OF G

Z" TOLERANCE AND PROTECTION

NO AGS

AGS PRESS.

SUPINATION

6I~I.IAY

w

2-3

1- -um

NADC-84021-60

0.06 G (upright) to 6.24 + 0.10 G (supine), an increase of 45j percent. It is therefore apparent that supination produces a

quite significant increase in G tolerance, whether the AGSbladders are inflated or not.

Valve Outlet Pressure: This factor was second in importancewith respect to affecting G tolerance, and from the viewpoint ofpractical application, was of primary interest. In general, asshown in Figures 7 and b, the greater the valve outlet pressure,the greater the G tolerance for both the supine and upright bodypositions. In Figure 7, the segments of the bars ascribed to AGSbladder pressurization relate to the upright body position only,while the segments ascribed to supination include an interactivefactor as well. Assuming the G protection (G tolerance with aninflated AGS and/or the supine body position minus upright G

- tolerance without AGS inflation) afforded by supination alone tobe represented by that measured when no pressure was fed to theAGS bladders, Figure 7 includes additional protection of 0.22,

A 0.27, and 0.31 G as part of supination for, respectively, low,-medium, and high valve outlet pressures. Protection afforded bysome sort of synergistic effect, when two or more G protectivetechniques are simultaneously applied, is further discussed laterin this report.

Paired t-tests were made to compare the differences in Gtolerance for the three levels of SCAG valve outlet pressureacross all other independent variables (subject, body position,SCAG valve mode of operation, and G onset time). The results ofthese tests are shown in Table 6. The null hypothesis tested herewas that the mean difference in G tolerance for any two levels ofSCAG valve outlet pressure was equal to zero. As shown by theentries in the table, the null hypothesis was emphaticallyrejected for all three possible comparisons. These findingstherefore lend support to the proposition that the levels of SCAGvalve outlet pressure used in this study were associated withdistinct differences in Gtolerance.

Based on a- linear, first order model to describe theSrelationship between G tolerance and SCAG valve outlet pressure,[ and using the method of least squares, estimates were made of the

1mmmslope and Y-intercept of the fitted straight lines for the uprightand supine body positions (Figure 8). The means of G tolerancefor the B and I modes ("Mode" was shown in Table 4 to be a non-significant factor as a variation source) were combined with Gtolerance values for the no valve outlet pressure conditions toconstruct the analysis of variance summarized in Table 7. Theresidual sum of squares was divided into "pure error" and "lack offit", the latter with respect to fitting the data to the linearmodel. The fact that the ",lack of fit"' mean squares for'both bodypositions were not significant indicates the adequacy of the modeland substantiates the use of the residual, mean square to evaluateregresion as the source of variation (5). As shown in the table,overall regression was 2a, very highly siqnficant source ofvariation. The maximum R obtainable with ihese data was about'50 percent for ?he upright case and 38 percent 2or the supine.The values of R actually attained by the fitted model havealmost the same values, thereby accounting for 96 percent(upright) and 99 percent (supine) of the fit.

24

i * - - . . ...

NADC-84021-60

•• 71

6-SUPI'

iliiili• 5 / '=4 •84 + 1.311

o UPRIGHT

Y=3.1•+0.79X

•i2-n~ iim

eniD 2

I _ _ _ __ _ _ _ _

"•!•0 1• 2

=* = PRESSURE GRADIENT (pSi0/0)

Ii Figure 8. Best fit regression lines for G-tolerance on SCAGvalve outlet pressure gradient (psig/G).

1 25II I II | _______________

-_- -- _---. ti

i i i i i -- !! ! ' --

NADC-84021-60

Table 6. Comparisons of G Tolerance Differences for SCAG ValveOutlet Pressures Across All Other Independent Variables

SCAG Valve Outlet Pressures

Medium High

- = 0.24 D = 0.56s5 = 0.06 s5 - 0.07

Low t = 4.09 t - 7.44p < .001 p < .001

D = 0.25sb - 0.06

Medium t = 4.03p< .001

Abbreviations: D = mean difference in G tolerance between higherlower SCAG valve outlet pressuresstandard error of the mean difference,

t = value of paired t-test (two-tailed) for 71degrees of freedom

p = probability of t value

--Iii

!'

.1, 26

NADC-84021-60

Table 7. Analysis of Variance Showing Regression of G Toleranceon SCAG Valve Outlet Pressure

UPRIGHT

Source df Sum of Squares Mean Square F P

- Regression 1 22.077 22.077 64.58 <.001

Residual 70 24.272 0A342

Lack of Fit 2 1.035 0.527 1.54 NS*

Pure Error 68 23.237 0.342

J Total (corr.)71 46.349

M x. R2 _ (46.349 - 23.237)j46.349 = 0.499R' attained by fitted model - 22.077/46.349 - 0.4760.476/0.499 x 100 - 96% explained

SUPINE

Regression 1 30.333 30.333 42.73 <.001

Residual 70 49.692 0.710

Lack of Fit 2 0.260 0.130( 0.18 -NS

I Pure Error 68 49.432 0.727

_ Total (corr.)7J1 80.025

IMx. R2 (80.025- 49.432)/80.025 - 0.382-R- attained by fitted model - 30.333/80.025 - 0.3790.379/0.382 x 100 - 99%, explained

*NS indicates not significant .(p:.05)

I! 27

I* ,'i , Ih . -L, , l i ,i i , J . I

NADC-84021-60

Inferences about the two parameters ('slope and Y-intercept)of the model were made for both the upright and supine bodypositions (5). Table 8 summarizes the pertinent information.Although the 95 percent confidence intervals of the upright andsupine Y-intercepts do not overlap, those of the two slopesoverlap slightly. A t-test 'to evaluate the hypothesis of nodifference between slopes yielded a value of 1.8986 for 140degrees of freedom, just short of the value of 1.96 needed forrejection of the hypothesis at the p - .05 level. As shown inSTable 6, the hypotheses were rejected that both parameters wereequal to zero.

G Onset Time: Table 4 contains data showing the effect of Gonset time. For the condition of no AGS bladder pressure, one wayanalyses of variance were made to evaluate the effect of G onsettime on G tolerance; these are shown in Table 9 for the uprightand supine'body positions. For both these body positions, G onsettime is not, significant. Note the much greater variance presentwhen the subjects were supinated. This information is alsoevident from examining Figure 9. Analyses of variance were alsomade for the effect of G onset time on G tolerance when the AGSbladders were inflated. Data entries for the upright bodyposition-were the means of B and I mode values, while data entriesfor the supine body position were- the individual values (Table10). Again, for both body positions, G onset time is notstatistically significant. However, because the: F value for thesupine body position does approach the value necessary forsignificance at the p - .05 level (3.10), paired t-testswere made on this data. Comparing .G tolerance for 2 and 8 s Gonset times, a value' of t 3 s - 4.19 was calculated, withp < .001. Comparing 4 and 8 s 3 onset times, t. - 2.22, withp < .05; for 2 and 4 s G onse-t times, t 5 -1.82, with .05 <p < .10. Therefore, when, the G onset t Lines were separated byonly 2 s, apparently there was no difference in mean Gtolerance. Doubling, the, difference in G onset time produced asignificant decrease in mean G tolerance, and tripling -thedifference caused -a very, highly significant decrease in mean Gtolerance. The relations between G tolerance and G onset timesI !are shown in Figure 9.AGS Comfort Assessment 'Mean AGS comfort scores for each subjectIare shownin Table 11. Paired t-tests Showed no significantdifference in mean AGS comfort scores between' Modes B and- I in theupright body position (t c - 0.21, p > 0.8), and in the supinebody position (ts - 1.45, -0.2 < p < 0.5). The difference in meancomfort scores for -the upright and supine body positions was alsoevaluated using the paired t-test and found to be non-significant(t, - 0.10, p >' 0.8). The overall mean comfort scores of thesubjects, shown in Table 11, were then subtracted from theirindividual comfort scores to obtain adjusted 'comfort scores. Meanadjusted comfort- scores are presented in Table 12 for theconditions of thii study.. To-way analyses of variance: were- made] on the- adjusted comfort scores to determine the relative effect ofAGS bladder pressure and G onset time. The results of theseanalyses for each of the subjects are. shown in Figure 10. WhileAGS bladder pressure played a statistically -significant role with,

-j9 -28

mob"-- .. .-- *--

-' S

NADC-84021-60

Table -8. Inferences about Two Model Parameters, B0 and 01a , forthe Regression of G Tolerance on SCAG Valve Outlet-Pressure

Body Position

-Upright Supine

95% C.I.b 2.8401 _5 so _S 3.3645 4.4641 S B00 S 5.2147* 0.5908 01 : S 0.9864 0.9086 :S B01 _ 1.7098

H0 : Bo = ou 2 3 . 6 6 3 6 d 25.7964

H0 : 01 -0 7.9721 6.5362

s o0 and 'Bi are the model parameters for b0 , the Y-intercept, andbl, the slope, of the linear regression curve.

b Confidence Interval

c The null hypothesis that the parameter equals zero.

d -Calculated value of t. The value of t for 70 degrees of freedomat the p = .05 level is approximately 2.

129,

2!-'

52

NADC-84021-60

Table 9. Analyses of Variance of G Tolerance for G Onset Timeswithout AGS Bladder Inflation

UPRIGHT

Source df Sum -of Squares Mean Square F P

G Onset Time 2 0.02 0.01 0.06 NS*

Error 15 2.88 0.19

Total 17 2.90

SUPINE

G Onset Time 2 0.30 0.15 0.29 NS

Error 15 1.69 0.51

Total 17 7.99

*NS indicates not significant (p>.05)

--,

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NADC-84021-60

z >1

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to

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.........- . ......

NADC-84021-60

Table 10. Analyses of Variance of G Tolerance for G Onset Timeswith AGS Bladder Inflation

UPRIGHT

Source df Sum of Squares Mean Square F P

G Onset Time 2 0.19 0.10 0.22 NS*

Error 51 21.93 0.43

Total 53 22.12

SUPINE

G Onset Time 2 5.11 2.55 2.66 NS

Error 105 100.69 0.96

Total 107 105.80

*NS indicates not significant (p>.05)

I

I _2 -

T.

NADC-84021-60

Table 11. Mean AGS Comfort Scores (N = 9)

SUBJECT

UprightMode 1* 50.33 47.56 56.11 70.56 68.33 62.78Mode B 67.22 49.44 54.44 61.11 78.33 50.83

SupineMode I 67.78 46.67 57.78 66.11 51.89 55.56Mode B 68.89 57.56 50.00 67.22 61.11 70.83

Mean 63.56 50.31 54.58 66.25 64.92 60.00

• Mode of SCAG valve operation. See text for explanation.

i3

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NADC-84021-60

t-o in % in2 cm---- 0" . . • . .

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NADC-84021-60

SUMMARY OF TWO - WAY ANALYSES OF VARIANCE

ON ADJUSTED COMFORT SCORES

UPRIGHT M3J Sup,

20- SOURCE: AGS PRESSURE

S10-

" " p = 0.05

I - U0 S1 S2 S3 S4 S5 S6,SMJECTS

4- ,SOURCE: ONSET TIME

---------------------- 0.05

1!0 S S2 S3 S4 S5. S6•

! tigure 10. Relative effects of AG-S bladder pressure and G onsetS~time on adjusted comfort scores.

335

NADC-84021-60

respect to adjusted comfort scores for most of the subjects, Gonset time was not a significant factor for any of the subjects.

Mean adjusted comfort scores and their standard errors forboth body positions and for the three levels of SCAG valve outletpressure are shown in Figure 11. The zero point on the horizontalscale corresponds to the overall mean comfort score of about 60.This lies somewhat less than half way between the adjectiveratings of "fair" and "good". As expected, at the high levels ofAGS bladder pressure, discomfort increased and the scores wereaccordingly reduced. The converse occurred with the low levels ofAGS bladder pressure.

A review of the comments made by the subjects regarding AGScomfort revealed that after about one-third of the G tolerancelimit runs, adverse remarks were made. Following the other two-thirds, AGS comfort was commented upon favorably or not mentioned.Adverse comments were concerned primarily with "tightness" or"pressure" of the AGS over those parts of the body situated underthe bladders. About 57 percent of adverse comments were madeafter runs in the upright body position, and the remaining 43percent after runs in the supine body position. Although onlyabout 29 percent of all the G tolerance runs were made with high

4I levels of AGS bladder pressure,, about 60 percent of these runswere accompanied by adverse comments regarding comfort. Another14 percent of the high pressure runs were rated poor or very poorwith respect to AGS comfort, with no additional remarks. About 13percent of the adverse comments were made following G toleranceruns where there were low AGS bladder pressures, and once whenthere was no bladder pressure. The remaining 27 percent ofadverse comments followed runs with medium bladder pressures. Theadverse comments were not distributed equally among subjects. Themost vocally critical subject made almost three times the numberof adverse remarks as the least vocally critical. Discomfortduring high bladder pressure runs constituted about a third of thecomments made by two subjects, about half made by three subjects,and about two-thirds made by the remaining subject.

DISCUSSION The results obtained in this study, and others like it,depend to a great extent upon the individuals who volunteer toparticipate as subjects. As expected, these persons differsubstantially in their physical characteristics and also showconsiderable variation in G tolerance. Other factors which mayaffect G tolerance, and which lie- entirely outside the purview ofthe investigator, may originate from activities or behavior inwhich the subject participates when he leaves the laboratory atthe end of the working day. Unfortunately, because ofexpenditures- required to conduct human centrifuge tests andbecause of limitations on the availability of qualifiedsubjects and of the centrifuge facility itself, the number of runsdevoted to any one study is necessarily quite limited. Thus, thecombination of intra-subject variability and limitations on theamount of data which can be collected make it quite difficult to"detect small differences in effects which may, nevertheless, bepresent. For these reasons, the question of whether the smallincrements in G protection resulting f rom the simultaneous use of

36

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NADC- 84021-60

00

LL 4)0o

w 0

0c 0~0

0 00 w (n

LL w

co

+1

00)

NADC-84021-60

the AGS and supination, as described earlier, are additive or not,is of particular interest.

In a recent paper, Cohen showed that a simple additivitymodel best predicted acceleration tolerance provided bysimultaneously combining various acceleration protectiontechniques (2). In fact, when a combination of protectivetechniques was used, a higher G tolerance was obtained than whenthe G tolerance due to each of the several component protectivetechniques in the combination were added, but the difference in G

, tolerance between the measured combined effect and the calculatedadded effect was not statistically significant. Crosbie comparedG protection afforded by the SCAG valve and the standard anti-Gvalve for upright subjects while relaxed or performing the M-1straining maneuver (4). An analysis of his data shows apronounced difference in G tolerance resulting from the combinedeffect of the M-1 maneuver and AGS bladder pressurization,especially with the SCAG valve, but again, no statisticaldifference can be demonstrated from the calculated sum of theindividual tolerance components.

Since the equipment and techniques used by Cohen and Crosbiewere essentially the same as those described in the present paper,a similar analysis of the protection afforded at the various AGSpressure levels was made for each of the subjects of this study inthe upright and supine body positions. As shown in Figure 12,except for subjects 4 and 6, the others exhibited a higher Gtolerance for the combination of AGS and supination than when thetolerances obtained separately for AGS and for supination wereadded. For the two subjects mentioned, just the reverse was foundat all three AGS pressure levels. The mean difference for allsubjects showed a G protection advantage when a combination ofprotective techniques was used, but this difference was notstatistically significant at any of the three AGS pressure levels(for low- AGS pressure, t5 - 1.34, p > 0.2; for mediuTm AGS

pressure, t5 - 1.46, P> 0.1; and for high AGS?• •p ressure, t~s--l.09, p > 0.2).

Therefore, the~present dataconfirms what was found in theprevious two studies, cited aboveand supports the concept of theadditivity of G protective techniques. In any case, from thepractical viewpoint, there have been no indications that any one GSprotective, technique interferes with, or somehow diminishes theeffectiveness' of another employed at the same time. The leastSeffect observed-when two or more such techniques are combined isadditivity; the possibility that greater control and precision inconducting acceleration studies may demonstrate a significantsynergistic effect is therefore primarily one of a more basicinterest.

Although the subjects who participated in this study wererepeatedly reminded to remain "relaxeda throughout the period ofacceleration runs, it is doubtful first, that the subjects wereactually relaxed,n and second, that their degree of relaxation"reained constant from run to run. No matter how experienced aScentrifuge rider a subject may be, there can be little doubt thatthe act of being strapped into a seat, being completely enclosedand isolated in a gondola, and listening to the dialogue andcountdown prior to, an acceleration run lead to some apprehension

38

NADCr84021-60

4j

04

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____ ___ ____ ___ __0 1 m

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39

.4 -17.____________

'NADC-84021-60

and tension. In fact, as reported by Webb (6), and oftenobserved by others, there is a distinct increase in heart ratewhich can be measured before the start of a centrifugeacceleration run, and this increase is greater when the subjectanticipates his exposure to higher G levels. To even remain in

4 the upright or supinated body position at 1 G requires some degreei t of muscular tension, which would be expected to increase

considerably with applied G. 'Probably the ultimate extent ofvoluntary muscular tension is exerted when subjects perform the M-1 respiratory maneuver during exposure to high G levels. None ofthe subjects in the present -study was observed to have performedthis maneuver, although normal respiratory and arm movements weremodified during G. No artifacts were seen on the ECG recordingswhich could be ascribed unequivocally to muscular activity. Itappears, therefore, that although not completely relaxed duringthe course of exposure to the G levels applied in this study, oursubjects maintained sufficient muscular tension to retain theirposture and to perform the rather precise wrist and arm movementsrequired to control the LED display which measured-peripheralvision.

Equation (1) is based on the assumptions that the simplehydrostatic model of the cardiovascular system is valid and thatthe mechanism of G protection provided by the AGS remains

* unchanged when the body position is significantly altered bysupination. If these assumptions hold, then the degree ofprotection afforded by the AGS when pressurized in accordance withequation (1) should be the same for both body positions. In orderto test this hypothesis, a comparison was made, using the pairedt-test, between AGS protection (G tolerance using the AGS minus Gtolerance without AGS inflation, for each set of correspondingexperimental conditions) in. the supine and upright body positionsfor each of the outlet pressure levels. Table 13 shows the

- results of this comparison. Since none of the t values calculatedis statistically significant, the hypothesis of no difference in Gprotection between the supine and upright body positions cannot berejected. Therefore, the data obtained in this study areconsistent with the application of equation (1) for determiningAGS bladder pressurization, at least where the seat back angleequals 15 degrees and 60 degrees.

As explained earlier', the end result of using what isreferred to here as the B mode of SCAG valve operation was to

l decrease the lag in AGS abdominal bladder inflation by severalhundred milliseconds, as compared to the I mode. Under theconditions of the tests as described, this small difference intiming of abdominal'bladder inflation had no discernible effect onG protection nor on.AGS comfort. In this connection, it should benoted that the maximum mean G onset rate (calculated 'by dividingthe difference between plateau and-baseline G by G onset time) was1.75 G/s in the upright body position and 2.75 G/s in the supinebody position. These G onset rates, while rapid, may have beeninsufficient to demonstrate the added. protection that earlierinflation of the abdominal bladder may provide. Preinflation ofthe AGS, i.e., bladder inflation before the onset of applied,G,has been used to reduce the volume of air required'to fill thebladders, and hence shorten bladder filling time. Thus, a

40

p .. + - ll? lll = -.lm l l si nV.. I~ I i l, , ..... .

NADC-84021-60

Table 13. Comparison of AGS Protection in the Upright andSupinated Body Positions

AGS Inflation Supine minus Upright Paired t-testPressure G Protection

Mean SEM t df P

Low 0.22 0.16 1.39 17 NS*

Medium 0.27 -0.15 1.81 17 NS

High 0.31 0.19 1.68 17 NS

*NS indicates not significant (p>.05)

441

I;)

itui 41

_NADC-84021-60

recently developed anti-G valve used by the U.S. Air Force,designated- HFRP, allows for the use of 0.2 psi at 1 G forpreinflation (1), and a preinflation pressure of only 0.05 psihas been shown to be effective with the SCAG valve in decreasingthe lag in bladder pressurization with the- onset of G (2).Because some pilots object to having their AGS even partiallyinflated at 1 G, this procedure was not followed inr this study.Since the lag in bladder inflation between the B and I modescaused no detectable differences in the dependent variables, it isdoubtful if changes due to preinflation would have beensignificant.

4 Selection of the low and high levels of SCAG valve outletpressures was arbitrary. It was desired to have sufficient

4I differences from -the medium level to obtain observable changes inthe dependent variables, without incurring pain in the high levelcase or totally ineffective G protection in the low level case.The interactions of SCAG valve -outlet pressure with G onset timeand mode of valve operation were unpredictable. A review of theliterature dealing with AGS bladder pressurization levels failedto provide much guidance, because of rather marked -differences inequipment and techniques used by the various investigators.However, it appears from the mean adjusted comfort scores thatserious pain was avoided with the high pressure levels, althoughconsiderable discomfort was experienced at times, especially inthe supine body position. The medium pressure level was evidentlyclose to what the subjects experienced as adequate comfort. Forthe upright body position, the medium level was somewhat greaterthan the upper limit of valve outlet pressure allowed in themilitary specification (see Figure 5). The low SCAG valve -outletpressure was -the one which overlapped, to the greatest extent,with the pressure range prescribed in the military specification.

V ~If the adjusted comfort score of zero, which in Figure 13.appears reasonable for the- upright body position, is also acceptedfor the supine body position, then it would seem that a slightlygreater bladder pressure could have been used for the middlelevel, supine body position. The large swings in comfort seen forthe high and low AGS bladder pressures for the supine bodyposition may be an indication that the selection of 25- percent of__•~ii ostion middl leel pnidrtontaeh slcinof ecn or•mm the middle level pressure gradient could have been reduced by 5-or10 percent in determining the low and high pressure gradients to

i apply. Of course, if this were done, then differences in Gtolerance due to these reduced pressure gradients would be moredifficult to detect.

'The relevance of AGS -comfort ratings and comments to- thesituation in- actual aircraft flight is probably debatable. In thelaboratory situation, the subject has the task of concentrating on-

*...how the AGS feels, and he is therefore-probably more critical inhis evaluation than a pi-lot would be, especially if the latterwere preoccupied with executing a series of air combat maneuvers.This problem -can only be resolved by flight testing the SCAG'valveunder controlled conditions which- are designed to duplicateoperational aircraft maneuvers of interest. Fortunately, the SCAGvalve can be readily programmed to produce a variety of outletpressure responses, and it is -contemplated that such flight tests

Will commence in the near future.1~ ______42

,...

NADC-84021-60

SUMMARY G tolerance was increased when relaxed subjects ridinga centrifuge were supinated (seat back angle of 60 degrees), ascompared to when they sat upright (seat back angle of 15- degrees).When wearing an anti-G suit (AGS) with inflated bladders, Gtolerance increased in both the supine and upright body positions.These increases were linear with increases in AGS bladderpressure. Changing G onset time by a factor of two and fourshowed a consistent effect only for the supine body position withAGS bladder inflation: G tolerance decreased as G onset timeincreased. Changing the mode of operation of a recently designedservo controlled anti-G valve regulating AGS bladder pressure hadno effect on G tolerance nor on AGS comfort. Comfort was alsounaffected by G onset time, but high AGS bladder pressures reducedAGS comfort scores and elicited adverse comments. Results of thisstudy supported the hypothesis that G protection -provided bysimultaneously applied anti-G techniques is additive. They alsowere compatible with the hydrostatic model of the circulatorysystem with respect to the pressure in the AGS bladders requiredto provide G protection when body posture was changed.

4

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NADC-84021-60

REFERENCES

1. Burton, R. R., R. M. Shaffstall, and J. L. Jaggars.Development, text,, and evaluation of an advanced anti-G valve forthe F-15. Aviat. Space Environ. Med. 51:504-509, 1980.

2. Cohen, M. 1. Combining techniques to. enhance protectionagainst high sustained accelerative forces. Aviat. Space, andEnviron. Med& 5,4338-342t 1983.

3.. Crosbie, R. J. Directional control of accelerative forces inceatrifuge.bIy syst4m,`*ý gimbals. J. Aviat. Med. 27:505-51i, 1956.

4. irosbie, JU J. A .ervo-controlled rapid response anti-G valve.Navl Ar C~veophti Centeri reportý NADC-83087-60 of 17 October

1983.

5. Draper, N;R.+ And u., Smtit. Applied Regression Analysis, (2nded.). New York: Jofi ai,,ley ','and Sons, Inc., 1981.

6. Gell, C. F., and&H. N. Hunter. Physiological investigation ofincreasing resistance to black-out by progressive backward tilt tothe supine position. J.. Aviat. Med. 25:568-577, 1954.

7. Military Specification MIL-V-9370D (AGS) Amendment 1. Valve,automatic, pressure regulating,. anti-G suit. U.S. GovernmentPrinting Office. 5 May 1972.8. Webb, M. G. Some effects of acceleration on human subjects. J.

Aviat. Med. 29:879-884, 1958.

APPENDIjX A

Definition of Acceleration Figure 13 illustrates the componentsof accelertion and the terminology as used in this report (8).Three mutually perpendicular accelerations, shown as •At, Av, andAn, act on the subject when he rides the DFS,: At, thetangential acceleration, is proportional to the angularacceleration of the DFS arm, and is therefore of significancewhenever the angular velocity of the arm changes; Av, thedownward acceleration due to gravity remains unchanged at 1gbefore, during, and after the centrifuge run; Ar, thecentrifugal acceleration, changes as the square of the angularvelocity of the arm, and tends to displace the subject's body and

tits contents f ootward, when the subject rides with his headdirected toward the center of arm rotation. The resultantacceleration, G, is what is referred to as "GO or accelerationn tis reor ----

' 763 the subject is seated Oupright" (seatback angle 15degrees), before the centrifuge arm is turned as well as after: itcomes to rest, only A, acts on the subject, and therefore he issubjected to 1 G. Since this acceleration is applied essentially-along the 'long axis. of his spine, the inertial loading heexperiences is 1 Gx (by definition). By manipulation of the DFS

. gimbals, the G applied to the upright-seated subject during the

[ 44

124 _WNW_

- -- - ., -- _. . I I I.-I

I1 tNADC-84021-60

-,,,AXIS OF-- • •i• ROTATION

"DFS ARMDIRECTION OF

jARM ROTATION

TEST LOAD

m,\

At-

\I -, -

If I I,-G: \r F~T I

S I ,I

Figure 13. ,Diagram showing G nomenclature.

45

- --- -

NADC-84021-60

acceleration profile is maintained parallel to the long axis ofhis spine, resulting in a Gz inertial loading which is numericallyequal to G. When the subject is placed in the supinated bodyposition (seatback angle - 60 degrees), before and after rotation,of the centrifuge arm, only A acts on the subject and -he istherefore -subjected to I G. Jowever, because only a fraction(about 70- percent) of AV is:-directed parallel to his spine, h•experiences a head-to-foot inertial load of about 0.7 Gz.During the acceleration profile, when the -centrifuge arm isrotating, the subject is positioned by the DES gimbals toexperience a Gz inertial load which continues to be approximately70 percent of the applied G. The distinction between the

- resultant acceleration, G, and the head-to-foot inertial load- (Gz)it produces, cannot be neglected.

1 The actual fraction depends on several factors, including theanatomical arrangement of the subject's cardiovascular tree.

I-4

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; ~ ~ ~ ~ ~ ~ ~ . .6•,, , I I h

D I S TR I B U T 10 N L I S T (Cont d)

No. of Copies

Royal Air Force Institute of Aviation Medicine,Farnborough- U.'K.

Defense & Civil Institute of Environmental Medicine,Downsview, Canada ............ ......................

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SInstitute of Aviation Medicine,, Oslo, Norway .......... ICommander, Naval Air Development Center ................ 3

1 (3 for Code -8130)

iiiip

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DISTRIBUTION LISTREPORT NO. NADC-84021-60

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L_