RES351 Paper
HUMANFACTORS, 1994,36(2),327-338 Fatigue inOperational Settings:Examples from theAviation Environment MARK R.ROSEKIND, NASAAmesResearch Center, PHILIPPA H.GANDER, SanJose State University Foundation, DONNAL.MILLER and KEVIN B.GREGORY, SterlingSoftware, ROY M.SMITH, KERI J.
WELDON, ELIZABETH L.CO, and KAREN L.McNALLY, San Jose State University Foundation, and J.
VICTOR LEBACQZ, NASAAmesResearch Center, Moffett Field,California The need for24-h operations createsnonstandard andaltered workschedules that can lead tocumulative sleeplossandcircadian disruption. Thesefactors canlead to fatigue andsleepiness andaffect performance andproductivity onthe job. The approach, research,andresults ofthe NASA AmesFatigue Countermeasures Pro- gram aredescribed toillustrate oneattempt toaddress theseissues inthe aviation environment. Thescientific andoperational relevanceofthese factors isdiscussed, and provocative issuesforfuture research arepresented.
INTRODUCTION Today, 24-hoperations areacritical com- ponent ofmaintaining ourtechnological so- ciety. Many different typesofoccupations and industries relyonround-the-clock opera- tions, including healthcare,public safety, service andmanufacturing industries,mili- tary operations. andtransportation. Esti- mates arethat oneinfive American workers is ashiftworker, workingsomeformofnon- standard oraltered workschedule (Officeof Technolo Assessment, 1991).These20mil- lion American shiftworkers areexposed to major disruptions intheir physiolo , social activities, andfamily lives.Theprincipal physiological disruptionoccursintwo areas:
sleep andcircadian rhythms.
1 Requests forreprints shouldbesent toMark R.Rose- kind, NASA AmesResearch Center.MailStop262-4. Mof- fett Field, CA94035-1000.
Sleep isavital physiological function,and obtaining even1h less than required canaf- fect waking levelsofsleepiness (Carskadon and Dement, 1982).Sleeplossmay beacute or, ifoccurring continuously overtime, may result inacumulative sleepdebt(Roth, Roehrs, Carskadon, andDement, 1989).
The suprachiasmatic nucleusinthe hypo- thalamus isapacemaker for24-h physiolog- ical and behavioral rhythms.Circadian (about 24h)rhythms govemsleep/wakeful- ness, motor activity, hormonal processes, body temperature, performance, andmany other factors. Corebody temperature isoften used asabiological markerofcircadian po- sition andisrelated tothe fluctuations seen in sleep/wakefulness. performance,hormone secretion, digestion, andother physiological activities. Theminimum ofthebodytemper- ature rhythm (whichtypically occursat3:00 to 5:00 a.m. daily) isassociated withsleep, 328-June1994 low motor activity, decreased performance, and worsened mood.Disturbances of24-h bi- ological rhythms maybeacute orcontinue over longperiods, resulting inchronic desyn- chronization betweendifferent physiological systems. (Forbackground inthis area, see Dinges. 1989;Mistlberger andRusak, 1989; Monk,1989.) Cumulative sleeplossandcircadian dis- ruption canlead todecreased wakingalert- ness, impaired performance. andworsened mood (Bonnett, 1985;Broughton andOgilvie, 1992). Individuals oftenusetheword "fa- tigue" tocharacterize theseexperiences. Es- timates suggestthat75% ofnight workers ex- perience sleepiness onevery nightshift,and for 20% ofthem, sleepiness isso severe that they actually fallasleep (Akerstedt, 1991).Al- though manyfactors mayaffect thesubjec- tive report offatigue (e.g.,workload, stress, environmental factors),themost substantial empirical datasuggest thatthetwo principal physiological sourcesoffatigue aresleep loss and circadian disruption.
Fatigue isaconcern inmany operational settings thatrequire 24-hactivities (Officeof Technolo Assessment, 1991).Decreased performance relatedtosleep lossand circa- dian disruption hasbeen implicated insome major disasters, suchasthe Exxon Valdez, Three MileIsland, andBhopal accidents (Of- fice ofTechnolo Assessment, 1991).Al- though thepotential risksofsleep lossand circadian disruption exist,theydonot dimin- ish society's needforcontinuous 24-hopera- tions. Therefore, itis critical thattheextent and impact offatigue inoperational settings be understood. Strategiesandcountermea- sures should bedeveloped andempirically evaluated todetermine approaches thatwill maximize performance andalertness and help tomaintain anadequate marginof safety. This article describes aNational Aeronau- tics and Space Administration (NASA)pro- HUMAN FACTORS gram, theapproach, methods,research.and results ofwhich aredesigned toaddress these issues inthe aviation environment. Itpro- vides anexample ofhow, inone mode of transportation, fatiguehasbeen empirically studied toprovide relevant datatoboth the scientific andoperational communities.
NASA AMES FATIGUE COUNTERMEASURES PROGRAM Program GoalsandResearch Approach In 1980, responding toacongressional re- quest, NASAAmesResearch Centerspon- sored aworkshop thatexamined whether "the circadian rhythmphenomenon, also called jetlag," wasofconcern (National Aero- nautics andSpace Administration, 1980,p.
1). The workshop participants concludedthat "there isasafety problem, ofuncertain mag- nitude, duetotransmeridian flyingandapo- tential problem duetofatigue inassociation with various factorsfoundinair transport operations" (abstract).TheNASA AmesFa- tigue/Jet LagProgram (latercalled theFa- tigue Countermeasures Program)wascreated to determine themagnitude ofthe problem and itsoperational implications. Threepro- gram goals wereestablished, whichcontinue to guide research efforts:(1)todetermine the extent offatigue, sleeploss,andcircadian dis- ruption inflight operations; (2)todetermine the impact ofthese factors onflight crewper- formance; and(3)todevelop andevaluate countermeasures tomitigate theadverse ef- fects ofthese factors andtomaximize flight crew performance andalertness.
The overall research approach hasbeen to integrate datacollected fromfieldstudies during regular flightoperations withfull- mission, high-fidelity flightsimulation stud- ies and with results fromcontrolled labora- tory experiments. Eachofthese research approaches hasstrengths andweaknesses from bothascientific andanoperational FATIGUEINAVIATION viewpoint. Fieldstudies maymore accurately reflect real-world conditions butareinher- ently difficult toconduct because, forexam- ple, research protocols mustnotinterfere with regular operational proceduresor safety. Also,itis virtually impossible tocon- trol allpotential contributory factorsinfield studies, andthere arelimitations tothe em- pirical measures thatcanbetolerated bysub- jects intheir usual workenvironment.
Laboratory studiesprovide acontrolled en- vironment formanipulating specificindepen- dent variables anddetermining theoutcome in precise ways.However, attemptstogener- alize these findings tothe more complex op- erational settingmaygreatly limittheoper- ational relevance oflaboratory studiesthat cannot incorporate allofthe potential inter- vening variables.
Full-mission, high-fidelityflightsimulation studies provide aunique opportunity toma- nipulate thespecifics ofatrip scenario and measure awide range offlight variables.
However, constraints onthe simulation envi- ronment mustbeconsidered (e.g.,realism, costs). Clearly, theintegration ofall three ap- proaches inasingle program hasimportant advantages, andtheprogram hasconducted studies usingeachofthese research ap- proaches tocapitalize ontheir unique strengths.
Measures The program usesadiverse rangeofempir- ical measures toevaluate fatigue.Inany given study, themeasures aredetermined by the specific hypotheses andobjectives ofthat particular study.Theinitial fieldstudies ex- amining theextent offatigue, sleeploss,and circadian disruption utilizedacombination of self-report andphysiological measures.
The self-report measuresincludedaback- ground questionnaire andapilot's daily logbook. The background questionnaire collected June 1994-329 demographic dataandinformation onflight experience, sleep,meals, exercise, andgen- eral health. Italso included somestandard- ized surveys, suchasthat forpersonality style. The pilot's dailylogbook, whichispocket- sized, contains information aboutflightand duty times, sleepquantity andquality. mood, meals, exercise, physicalsymptoms, and comments (e.g.,operational events,environ- mental factors). Thesedataarecollected a maximum ofthree daysprior toatrip sched- ule, throughout atrip, andforamaximum of four days after thetrip.
The first physiological variableassessed was core body temperature, whichallowed the determination ofcircadian phaseand measurement ofamplitude. Anambulatory recorder (Vitalog, Inc.)collected continuous temperature dataviaarectal thermistor, heart rateinformation viachest electrode placements, andactivity detected byamo- tion sensor wornonthe nondominant wrist.
This portable recordercollected andstored the data forupto10days.
Over theyears, thesophistication and range ofmeasures hasincreased. Continuous portable recording ofelectroencephalo- graphic (EEG),electro-oculographic (EOG), and electromyographic (EMG)activity isob- tained usinganOxford Medilog 9200re- corder. Thisinstrument providesuptoeight channels ofphysiological data,which are continuously collectedinanalog formontoa high-quality cassettetape.TheMedilog can collect continuous dataonone tape forupto 24 h.The tape islater played backonascan- ning system thatallows detailed analysisof standardized sleepvariables (e.g.,sleep la- tency, totalsleep time, amounts ofrapid eye movement [REM]andnon-REM sleep,and awakenings). The Medilog canprovide bothsleep and wakefulness data.TheEEG information can be analyzed forEEG frequency changes(e.g., 330-June1994 alpha andtheta activity), andtheEOG data reflect sloweyemovements, whichareasso- ciated withphysiological sleepinessduring wakefulness (AkerstedtandGillberg, 1990).
In addition tothese physiological mea- sures, arecent studyincorporated avigilance performance measurethatuses reaction time to assess sustained attention(Dingesand Powell, 1985,1988). Thispsychomotor vigi- lance task(PVT) isalO-min simplereaction time testthat probes central nervous system (CNS) capability. Ithas been demonstrated to be sensitive tothe effects ofsleep lossand circadian disruption anddoes nothave asig- nificant learning curve,unlike manyother performance tests(Dinges andKribbs, 1991).
The PVT data areespecially usefulasa metric because theycanbecompared with previous findingsfromsleep deprivation and sleep disorder studies.ThePVT does notrep- resent aspecific flightperformance variable.
Instead, itprovides ameasure ofCNS capa- bility, especially ofsustained attentionand vigilance performance, whichareimportant factors inmany operational settings,includ- ing aviation.
New measures areadded asstudy objec- tives expand intodifferent areas.Forexam- ple, anupcoming projectwillrequire the measurement ofnoise levels withasound pressure meterduring flightandblood oxy- gen saturation usinganoximeter during sleep. Theprincipal measures usedwere:
Background questionnaire (e.g.,demographics, personality) Survey/questionnaire data(e.g., operational is- sues) Logbook subjective report(e.g.,pilot's dailylog- book) Observationallbehavioral data(e.g., cockpit ob- server log) Physical performance andmental functioning tests (e.g., psychomotor vigilancetask) Long-term continuous recordingofmotor activ- ity (actigraphy) Long-term continuous recording(viaVitalog) of physiological parameters(e.g.,corebody tem- perature, heartrate) HUMAN FACTORS Continuous physiological recording(viaMed- ilog) ofbrain (EEG), eye(EOG), andmuscle (EMG) activity Typically, oneortwo NASA researchers/ observers accompany volunteerpilotsduring a trip tocollect themeasures andprovide guidance regarding theprotocol.
Over thepast 12years, studies havebeen conducted inavariety ofaviation andcon- trolled laboratory environments andinone full-mission flightsimulation. Theseprojects were often labor intensive, spannedseveral years fromdesign toimplementation toanal- ysis andreporting ofresults, andoften in- volved collaborations. Supportandcollabo- ration inthe United Statescamefromthe Federal Aviation Administration (FAA),the National Transportation SafetyBoard (NTSB), aircarriers, pilots,pilotunions, and the military. Someofthe international stud- ies involved worldwide collaborations with research andflight operations groupsfrom the United Kingdom, Germany,Japan,and other countries. References reportingthere- sults from many ofthe NASA studies and other significant programpublications are provided inthe appendix.
The results ofthese studies havebeencol- lectively organized intoanextensive data- base thatencompasses datafrom more than 500 volunteer pilots.Thisdatabase allows unique comparisons betweenoperational en- vironments inwhich similar measures were taken. Another critical factor insuccessfully col- lecting thesedatahasbeen theassurance of anonymity andconfidentiality forallofthe participants. Aftervolunteering forastudy, a pilot would receive anidentification number, and noname would everbeassociated with any ofthe data collected.
RESEARCH EXAMPLES Three studies willbehighlighted toprovide examples ofthe research approach, measures, FATIGUEINAVIATION and findings andtheoperational relevanceof the data.
Short-Haul Commercial Operations This study wasconducted toexamine the extent ofsleep loss,circadian disruption, and fatigue engendered byflying commercial short-haul airtransport operations (flight legs lessthan 8h; see Gander, Graeber, Foushee, Lauber,andConnell, inpress). In this study, 74pilots fromtwoairlines were studied before,during, andafter three- and four-day commercial short-haultrips.All flights tookplace onthe East Coast ofthe United Statesandoccurred throughout the year. Ofthe pilots contacted aboutthestudy, 85% agreed toparticipate. Asagroup, thepi- lots averaged 41.3years ofage and had, on average, 14.6years ofairline experience.
Physiological data(core body temperature and heart rate)andmotor activity wereob- tained every2min with theVitalog portable biomedical monitor.Usingthepilot's daily logbook, subjectsprovided subjective ratings of fatigue andmood every2h while awake and recorded theirsleep episodes andother activities (e.g.,meals, exercise, dutytime). All subjects completed abackground question- naire, andaNASA cockpit observer accom- panied crewsduring tripschedules.
The specific daytime andevening trips studied wereselected soas toprovide infor- mation abouttheupper rangeoffatigue re- ported bypilots inthese operations. Common features ofthe trip schedules includedearly report times(i.e.,forduty) andmultiple flight legs (average 5.5/day)overlongduty days.
The trips averaged 10.6hof duty perday and involved anaverage of4.5 hof flight time.
One third ofthe duty periods studiedwere longer than12h.The average restperiod was 12.5 hlong andusually occurred progres- sively earlier inthe day across successive trip days.
Data fromthedaily logbook demonstrated June 1994-331 that during tripnights, pilotstookabout 12 min longer tofall asleep, sleptabout 1.2h less, andawoke about1.4hearlier compared with their pretrip sleeppatterns. Thepilots reported thistripsleep aslighter andpoorer (with moreawakenings) thanpretrip sleep.
Subjective fatigueandmood wereworse dur- ing layovers thanbefore orafter thetrip or during flights. Significant time-of-day effects were found forfatigue, negative emotions, and activation ratings.Inthe first three rat- ings ofthe day following awakening, fatigue and negative emotionratingswerelow.
Thereafter theyincreased andreached their highest valuesinthe final rating priorto sleep. Predictably, activationratingsshowed the inverse ofthis pattern.
On trip days, pilots consumed morecaf- feine (mean = 3.4 servings) thanonpretrip days (mean = 1.9 servings) orposttrip days (mean = 2.7 servings), presumably tomain- tain alertness duringoperations. Caffeinewas consumed primarilyinthe early morning, which isassociated withtheearlier wake-up and duty times, andalso during themidafter- noon peakinphysiological sleepiness.During the trip schedule morealcohol (mean = 1.6 servings) wasconsumed thanonpretrip (mean = 0.5 servings) andposttrip (mean = 1.0 servings) days.Itcan beassumed thatpi- lots consumed thealcohol onlyafter coming off duty (presumably tounwind afteralong duty day), andinaccordance withfederal avi- ation regulations. Duringtrips,moresnacks were consumed, andthey were consumed earlier inthe wake period.
For 72pilots flying 589legs, heart ratesob- tained during takeoff, descent, andlanding were compared withmidcruise values.The pilot flying hadgreater increases inheart rate during descent andlanding thandidthepilot not flying. Thisincrease wasgreater under instrument flightrulethan under visual flight ruleconditions.
This wasoneofthe first field studies 332-June1994 conducted bythe NASA program, anditpro- vides aunique insight intothephysiological and subjective effectsofflying short-haul commercial operations.Itdemonstrated that these measures couldbeobtained inan oper- ational environment withoutdisturbing reg- ular performance ofduties. Thestudy results suggest severalsignificant operational con- siderations regardingfatigue.Forexample, the data showed thatthedaily dutydurations were double theflight durations andthat one third ofthe duty periods werelonger than12 h. Findings fromthisstudy suggest thatlim- itations onduty timeshould beconsidered, just aspilot flight timesarecurrently limited by federal aviation regulations. Also,the practice ofmaking pilotsreport forduty ear- lier onsuccessive tripdays, requiring earlier wake-up times,interferes withobtaining ad- equate sleep.Evenwhen thelayovers were relatively long,thecircadian systemwould generally inhibitfallingasleepearlier, and hence asignificant amountofsleep would be lost during tripnights. Therefore, whenpos- sible, dutyonsuccessive tripdays should begin atthe same timeoreven begin pro- gressively later,moving withthenatural tendency ofthe biological clocktoextend the day.
Finally, alcoholisknown todisrupt sleep dramatically andtherefore contributes tothe poor quantity andquality ofsleep obtained on trip nights. Alternate waystounwind after duty andtopromote sleepshould beidenti- fied andoffered (e.g.,cognitive-behavioral re- laxation approaches).
Long-Haul Commercial Operations This study examined howlong-haul (>8h) flight crews organized theirsleep during ava- riety ofinternational trippatterns andhow duty requirements, localtime, andthecirca- dian system affectthetiming, quantity, and quality ofsleep (Gander, Graeber,Connell, and Gregory, 1991).Dutyrequirements and HUMAN FACTORS local timecanbeviewed asexternaUenviron- mental constraints ontime available for sleep, whereas theinternal circadian system is amajor physiological modulatorofsleep duration andquality.
Subjects were29male flight crewmembers (average age = 52 yrs) flying Boeing 747air- craft onone offour commercial international trip patterns. Thisreport combined thedata from thefour tripschedules. Thepilot's daily logbook wascompleted priorto,during, and following thetrip tocollect self-reports of duty times andofsleep timing, duration, and quality, andsoon (i.e., thesame dataasinthe short-haul study).Corebody temperature, heart rate,andactivity usingtheVitalog por- table biomedical monitorwerecollected ev- ery 2min. Thecore body temperature, mea- sured witharectal thermistor, wasused asa marker ofthe underlying circadiantime- keeping system.
On average, theduty periods lastedabout 10.3 hand were followed by24.8 hoflayover.
During layovers thereweregenerally two sleep episodes. Theaverage sleep/wakeful- ness pattern was19hawake, 5.7hof sleep, 7.4 hawake, and5.8hof sleep. Pilotsgener- ally reported thatthefirst sleep ofthe layover was ofbetter quality andthat they fellasleep more easily andobtained deepersleepthanin the subsequent sleepepisode. Asthe length of sleep increased, therewasaconcomitant in- crease insleep quality ratings. Thecircadian system appeared toexert agreater influence on the timing andduration ofthe first sleep episode thanonthat ofthe second sleepofa layover, withapreference forsleeping during local night and/or waking upafter thetem- perature minimum. Theexception wasafter eastward flightsthatcrossed fiveormore time zones andproduced ahigh accumulated sleep debt. Thetime offalling asleepforthe second sleepepisode wasrelated tothe amount ofsleep already obtained. Ittypically occurred duringlocalnight, andtheduration FATIGUEINAVIATION was related tothe remaining timeavailable before duty.Theduration ofboth sleep epi- sodes waslonger whencrewmembers fell asleep earlier withrespect totheir circadian temperature minimums.
Subjective reportsofnaps taken during layovers wereobtained fromthedaily log- book. When thefirst sleep episode ofalay- over wasidentified asanap, itaveraged 2h in length, wasgenerally longerthanother naps, andfollowed significantly longerperi- ods ofwakefulness. Thesefirstnaps typically occurred inresponse toacute sleeplossasso- ciated withovernight eastwardflightsor westward flightscrossing fivetime zones or more. Other napsoccurred justprior tothe next duty period andeffectively shortened the length ofcontinuous wakefulness.
Crew members alsoreported intheir log- books theoccurrence ofnaps onthe flight deck. (In-flight restonthe flight deckisnot sanctioned undercurrent federalregula- tions.) Theaverage duration ofthe naps re- ported onthe flight deckwas46min (range, 10--130 min).Research observers accompany- ing thecrews alsonoted napsnotreported in the logbooks. Datacombining theresearch observers' notesandlogbook datasuggest that, onaverage, 11 % offlight crewmembers were taking theopportunity tonap when con- ditions permitted. Thedata donot indicate whether thesewereplanned napsoroccurred spontaneously inresponse tosleep lossand circadian disruption.
This study provides uniqueinsights into the physiological andsubjective effectsoffly- ing long-haul commercial operations.Thein- formation isscientifically provocativeand can betranslated intooperationally relevant considerations. Thefollowing aresome ofthe scientific considerations thatemerge from the results.
The flight schedules pushedthesleep/wake cycle intoaperiod (25.7h)different fromthat of the circadian system,thoughthetwo sys- June 1994-333 terns didnotbecome completely uncoupled.
Although thecircadian systemcontinued to influence thetiming andduration ofsleep ep- isodes, itwas unable toresynchronize and quickly adapttothe rapid, multiple time- zone shifts. Itisclear thatavariety ofexter- nal/environmental factors(e.g.,light, activ- ity, social cues)interact withinternal!
physiological factorstoaffect sleeptiming, duration, andquality. Theoperational rele- vance ofthe data iseasy todiscern. Forex- ample, current flightandduty timeregula- tions areintended toensure thatreasonable minimum restperiods areavailable forflight crews. However, thisstudy demonstrated that incommercial long-haulflightsched- ules, there arephysiologically andenviron- mentally determined preferredsleeptimes within alayover, andtherefore thetime available forsleep maybeless than theoff- duty timeavailable.
Planned CockpitRest As indicated fromtheresults ofthe previ- ous study, long-haul flightoperations involve sleep lossandcircadian disruption. Anec- dotal, observational, andself-report sources (e.g., those fromtheprevious study)indicate that sleep doesoccur onthe flight deck,de- spite federal regulations forbiddingin-flight rest. Itisunclear fromavailable datahow often thesenapsareplanned andhow often they occur spontaneously inresponse tosleep loss andcircadian disruption. Inconsider- ation ofthe available information regarding rest onthe flight deck,thefirst testofan op- erational fatiguecountermeasure wascon- ducted. ANASA/FAA studyexamined theef- fectiveness ofaplanned cockpitrestperiod to maintain and/orimprove subsequent perfor- mance andalertness inlong-haul, nonaug- mented international flights(nonaugmented = only primary crewrequired; augmented = extra crewneeded whenovercertain flying times; Rosekind, etai., inpress). 334-June 1994 A regularly scheduled 12-day,eight-leg trip that involved multipletrans-Pacific crossings was selected forstudy. Theflight legsaver- aged justover 9h and were followed byabout 25 hof layover. Priorto,during, andafter the 12-day trip,crew members completed pilot's daily logbooks, documenting sleepandduty times andother activities, andwore acti- graphs ontheir nondominant wrist.(Anacti- graph collects noninvasive activitydatafrom a motion sensor,providing anestimate ofan individual's 24-hrest/activity pattern;Cole, Kripke, Gruen,Mullaney, andGillin, 1992.) The middle fourlegsofthe trip schedule were studied intensively. EEGandEOG activity was continuously monitoredduringthese flight legsusing theMedilog recorder. Anex- tensive scientific literature demonstrates that self-reports ofsleep (e.g.,timetofall asleep, total sleep time)donot accurately reflect physiological activity(Carskadon etaI., 1976; Rosekind andSchwartz, 1988).Therefore it was critical todocument theamount ofphys- iological sleepobtained. Continuous EEG and EOG recordings takenduring theawake period wereusedtoassess physiological sleepiness. ThePVT wasused asameasure of vigilance performance andsustained atten- tion. Pilots alsogave self-report ratingsof alertness andmood atpredetermined times throughout theflight. TwoNASA researchers traveled withthecrews toimplement the procedures andcollect data.
The three-person Boeing747volunteer crew members wererandomly assignedtoei- ther arest group orno-rest group.Eachrest group member (12subjects) hada40-min rest opportunity duringthelow-workload portion of flights overwater. Crewmembers rested one atatime onaprearranged rotationwhile the other twocrew members maintained the flight. Theno-rest group(9subjects) hada 40-min controlperiodidentified whenthey were instructed tocontinue theirregular flight activities. Specificsafetyandproce- HUMAN FACTORS dural guidelines wereusedduring thestudy.
The first question waswhether pilots would beable tosleep during aplanned rest opportunity intheir cockpit seat.Therest group sleptduring 93%ofthe rest opportuni- ties. Onaverage, theyfellasleep in5.6 mins and slept forabout 26min. Whether ornot a benefit wasassociated withthissleep wasde- termined byexamining thevigilance perfor- mance measure andindicators ofphysiologi- cal sleepiness. Asexpected, theno-rest group showed performance decrements(i.e.,in- creased reaction timesandvariability onthe PVT) atthe end offlights compared withthe beginning offlights, onnight flights versus day flights, andonthe fourth studylegcom- pared withthefirst study leg.The restgroup, however, demonstrated positiveeffectsofthe brief napbymaintaining consistentlygood performance atthe end offlights, onnight flights, andonthe fourth studyleg.
Physiological sleepinesswasexamined by evaluating thesubtle EEGandEOG changes that indicate statelability. Previous research has demonstrated thatphysiological sleepi- ness isassociated withtheoccurrence ofEEG alpha ortheta waves and/or EOGsloweye movements. Thesephysiological eventsare associated withdecreased performance (Ak- erstedt, 1992;Akerstedt andGillberg, 1990).
Microevents (briefsleepevents) indicative of physiological sleepiness(theoccurrence of EEG alpha ortheta waves and/or EOGslow eye movements) lasting5sor longer were identified duringthelast 90min offlight, even during descent andlanding, inboth study groups. Overall, theno-rest grouphad microevents (mean = 6.37) indicative of physiological sleepinessatarate twice thatof the rest group (mean = 2.90).
The brief napappeared toact asan acute in-flight operational safetyvalveanddidnot affect thecumulative sleepdebtobserved in 85% ofthe crew members. Therestgroup members wereusually abletosleep during FATIGUEINAVIATION the rest opportunity, andthisnap was asso- ciated withimproved performance andalert- ness compared withtheno-rest control group. Thiswasthefirst empirical testofa fa tigue countermeasure conductedinan op- erational aviationsettingthatcombined physiological, performance,andsubjective measures.
Not only aretheresults scientifically inter- esting, butthey canbetransferred directly into operational considerations regarding planned rest.Based partly onthe results of this NASA/FAA study,anindustry/govern- ment working grouphasdrafted anadvisory circular forreview bythe FAA's Aviation Rulemaking AdvisoryCommittee. Thecircu- lar outlines specificguidelines forthe devel- opment andimplementation ofaprogram for controlled restonthe flight deck.Itshould be noted thatcontrolled restisonly onein-flight countermeasure andisnot thepanacea forall of the sleep lossand circadian disruption en- gendered bylong-haul flightoperations (Rosekind, Gander,andDinges, 1991).
Current Activities andFuture Directions In 1991, thename ofthe program was changed tothe Fatigue Countermeasures Pro- gram toemphasize thedevelopment and evaluation ofcountermeasures. Onearea of intense activity isthe analysis andwriting of a variety ofscientific andoperational publi- cations totransfer theinformation acquired over thepast 12years tothe scientific and operational communities. Anotherprojectin- volves astudy ofthe onboard crewrestfacil- ities onlong-haul aircraft.Bunksareavail- able forpilots whenaflight isaugmented (extra crewonboard) andtheflight length ex- tends beyond thatallowed forasingle crew.
This study willexamine thequantity and quality ofsleep obtained inonboard crewrest facilities, thefactors thatpromote orinter- fere with sleep, andtheeffects onsubsequent performance andalertness.
June 1994-335 Another majorproject isthe development and implementation ofan education and training moduleentitled" Alertness Manage- ment inFlight Operations" (Rosekind,Gan- der, andConnell, inpress). Itprovides infor- mation onphysiological sourcesoffatigue and how flight operations affectthesefactors and makes recommendations forfatigue countermeasures. Themodule isintended for any interested partyinthe aviation commu- nity, including pilots,aircarrier managers, schedulers, flightattendants, andfederal pol- icymakers. Potentialareasforfuture program activity includethedevelopment ofan expert scheduling systemthatincorporates known scientific andphysiological data,anexami- nation offatigue inregional airlineopera- tions, andfurther development andevalua- tion ofcountermeasures.
FUTURE CONSIDERATIONS FOR FATIGUE RESEARCH IN OPERATIONAL SETTINGS As issues ofsafety andhealth continue tobe raised regarding fatigueinoperational envi- ronments, moreresearch willberequired to address them.Major questions raisedin many operational settingsinclude, Whatis safe? Howlongistoo long todrive, fly,or operate atrain? Howmany nightshifts ina row istoo many? Howlongistoo long fora shift period? Howmany consecutive dayscan be worked safely?Howlongdoes ittake to recover afteranextended dutyorshift pe- riod? Howlongdoes ittake torecover after several consecutive dutyorshift periods? Do individuals needonenight ofsleep ortwo nights? Howcould napsbeused toimprove the situation? Howshould onedefine recov- ery: byphysiological adaptation,perfor- mance, orwaking sleepiness? Afterstarting a new shift schedule, howlongwill ittake to physiologically adapt?Whataretheeffects of changing fromanight shiftschedule toareg- ular daytime schedule onthe weekends and 336--June1994 then back tonight shifts? Howshould current hours-of-service regulationsbeevaluated? If they should bechanged, howshould theybe adjusted? Onwhat should suchchanges be based?
Each ofthe issues raised suggests awide range ofresearch activities. Theyalsorepre- sent theconcerns facedbythe 20million Americans currentlyworkingalteredornon- standard shifts.Thepoint ofthese questions is that thescientific researchwillbemost useful ifit is integrated withoperational con- cerns. There areother considerations aswell. Al- though generic research willhelp toset asci- entific foundation foraddressing theseoper- ational questions, itis also critical to understand thespecific requirements ofdif- ferent settings. Thetype ofshift schedule, task demands, timingofcritical tasks,and other factors suchasmeal availability and break schedules presentdifferent challenges.
Another areatoexamine isthe tremendous individual variationthatexists inresponse to sleep loss,circadian disruption, andperfor- mance changes. Different workandcorporate cultures willhave disparate attitudes, knowl- edge, andconcern abouttheseissues, andthis can affect workperformance andsatisfaction.
Also, there isvery little information regard- ing thelong-term (e.g.,months oryears) ef- fects ofsleep lossand circadian disruption on safety, performance, productivity,and health. Another majorareaisthe develop- ment andempirical evaluation ofcounter- measures. Theremaybeawide variety ofso- lutions thatwillmaximize alertnessand performance-for instance,thoseinvolving physiological strategies,displaydesign,or schedule design.Thisareacreates tremen- dous potential forevaluating newtechnolo- gies andstrategies.
One valuable approach isto coordinate and integrate resources andexpertise amongre- searchers, federalagencies, policymakers, HUMAN FACTORS and soon tomaximize thepotential effectof any given research projectoroperational im- plementation offindings. Itisoften critical that scientists beallowed accesstothe sub- jects' operational environment or,atmini- mum, tofully understand howthings workin a particular setting.Theclose coordination of scientific andoperational effortscanalso lay the foundation foradirect application ofpos- itive findings.
Clearly thereisalot ofimportant workto be done. TheNASA AmesFatigue Counter- measures Programispresented asamodel of one approach toaddressing someofthe issues raised. Itisnot theonly approach possible but ispresented tostimulate empirical re- search inapplied operational settings.
Human factorsresearch canplaya pivotal role inthe scientific investigation ofthese is- sues andinthe application ofthe findings to specific operational questions.Aslong as24-h operations arerequired tomaintain societal needs, theeffects ofsleep lossandcircadian disruption mustbeconsiderations inany op- erational setting.Howthese factors affectthe physiological andperformance capabilitiesof the human operator willbecritical tojob safety, performance, andproductivity.
ACKNOWLEDGMENTS We wish toacknowledge thesignificant contributions of the following: JohnLauber, CurtGraeber, ClayFoushee, and Charles Billings; WilliamReynard andLinda Connell at NASA Ames; KeyDismukes forathorough andcon- structive manuscript review;DavidDinges, Institute for Pennsylvania Hospital/University ofPennsylvania School of Medicine, forongoing collaboration; andtheFAA staff, volunteer pilots.aircarriers, andunions, whohave been critical tothe success ofprogram activities, APPENDIX: FATIGUE COUNTERMEASURES PROGRAM REFERENCES (PARTIALLISTING) Dinges, D.F., and Graeber, R.C.(1989, October). Crewfa- tigue monitoring.
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Date received: January25,1993 Date accepted: July22,1993
