- Email: [email protected]
Adverse effects of rotating schedules on the circadian rhythms of air medical crews timothy
BRIEF REPORT
Adverse Effects of Rotating Schedules on the Circadian Rhythms of Air Medical Crews Timothy C. Martin, BS, NREMT-P1 1.
Flight For Life, Mother Tyler, Texas
Key Words: aeromedical, sleep deprivation
Frances
Hospital,
circadian
rhythm,
Address for correspondence: NREMT-P, 13121 Southview TX 75240;TCM692@aol,com
T.C. Martin, BS Lane, Dallas,
Submitted: November 7,1994 Revised: April 20, 1995 Accepted: May 1, 1995 This paper was presented at the 14th Annual Air Medical Transpori Conference in St. Louis, MO., on October 4, 1993.
Air Medical
Journal
14:2
April-June
1995
Introduction Observations of the rhythmic nature of animal behavior date back to the time of Aristotle, who noted swelling of sea urchin ovaries during the full moon.1 “Sleep movements” of plants also were noted by the ancient Greeks, who attributed the phenomena to the presence or absence of sunlight. Circadian rhythm (Latin: circa meaning about, and diem meaning a day) is defined as an inborn, genetically programmed, self-sustained rhythm in behavior, physiology and metabolism, developed over evolutionary time that enables living organisms to cope with the 24hour daily rotation of the planet.’ One of the first experiments designed to test circadian rhythms in plants was done in 1729 by de Mairan, who illustrated that plant leaves open in the daytime even when kept in total darkness.2 This was the first presentation of evidence of an endogenous biological clock that functioned in the absence of zeitgebers (German for “time givers” or clues to the time of day). The term “free running” has been used to describe a rhythm in behavior pattern, or resultant metabolic pattern, that continues in the absence of any exogenous clues.1 The concept of freerunning biological clocks was discovered in 1832 by de Candolle, who placed plants in constant bright light.2 After a few days, the leaves opened and closed on a 22-hour cycle. This display indicated that the plant had its own independent day length. Circadian rhythms have endogenous and exogenous components; the former is dependent on a clocklike
mechanism, while the latter is driven by external time clues (zeitgebers).zThe endogenous clock appears to be responsible for the free-running day length, and light/dark cycles have been shown to be important in adjusting the human circadian clock. Many species of invertebrates demonstrate that circadian clocks have evolved mechanisms by which they frequently are reset to keep pace with changes in the local environment, most notably by being sensitive to the intensity of light.3 Controlled experiments have shown that humans have a 25.1-hour circadian clock that is constant and predictable but entrained to the 24-hour day by environmental clues.294Volunteers were studied by Weitzman and Czeisler in periods ranging from two weeks to six months, during which they were isolated from any zeitgebers. Subjects were permitted to eat and sleep at times of their own choosing, and after one week in the clue-free environment, they lagged behind their usual day/night schedules by almost eight hours. This implies that human internal clocks are reset on a daily basis.2 Forced changes in circadian rhythm produce sleep disruption and deprivation.2,5-7The circadian system influences performance through its effects on metabolic functions and on quality of sleep. Its rhythmicity and consistency is crucial to the maintenance of normal levels of body function and performance. The most obvious change occurs in sleep patterns, where sleep becomes shortened and disrupted by the displacement of the circadian rhythm. Pilots undergoing a shift change may find themselves awake in the a3
Circadian Rhythm and Shift Schedule Survey 1) How
many 08
Please
hours
a day are your flight crew members 0 12 0 24 0 Other-Please
fill in the average Sun
Mon
two-week
Tues
shift of a full-time
Wed
Thurs
Fri
(FCMs) scheduled explain FCM.
FCMs
have
a permanent
q Y
a check
or an x).
Sat
2) Do your FCMs have a permanent shift (e.g., permanent N Y 0 Permanent evenings 0 Permanent days 3) Do your
(With
to work?
days,
etc.)?
0 Permanent
nights
partner?
ON
4) Do your FCMs rotate shifts (e.g., days, Y N 0 Days => Evenings => Nights 0 Days => Nights
evenings,
nights
or days/nights)?
5) If FCMs do rotate shifts, how long do the rotations last? 0 2 Weeks 0 4 Weeks 0 6 Weeks 0 Other-Please 6) How
long does it take for the average Days => nights Nights => days Not Applicable
7) What
is the biggest
complaint
your
FCM to adapt
FCMs
have about
6a) Does your program permit FCMs to sleep? 0 Y q N take
10) What do you think the ideal shift schedule A) For personnel? B) For your program? many
flights
12) How
many 01
aircraft
many
FCMs
per month does 02
rotating
rotating
from:
shifts?
b) If not, is there a place for them to “relax”? 0 Y 0 N
9) Does your program’s shift scheduling 0 Y q N If yes, please explain:
11) How
explain
does
your
your program 03
into account
the FCMs
circadian
rhythm?
is:
program
average?
utilize?
juries appear to occur more frequently at certain times of the day because worker performance is affected by disruptions in the circadian rhythm.8 One study found that most injuries in shift workers occurred between 10 p.m. and 2 a.m. and that firefighters sustain more injuries during the night shift.8 A hospital-based survey on &ii work, sleep and accidents was carried out among 635 Massachusetts nurses.9 In comparison to nurses who only worked day or evening shifts, nurses who rotated shifts had more sleep/wake cycle disrup tion and nodded off more at work.9 The rotating nurses had twice the odds of nodding off while driving to or from work, and twice the odds of a reported accident or error related to sleepiness.9 People who have worked nights for several years continue to complain of fatigue and trouble adjusting.6 This is because the body is exposed to contlicting synchronizing clues: the work schedule demands activity at night and sleep during the day, whereas all other environmental and social clues point to activity during the day and sleep at night.5 Animal models suggest diminished longevity as a consequence of rotating shifts, and in Japan there is legal precedent for considering night work a compensable cause of premature death.2 The purpose of this study was to ascertain how many programs use a rotating schedule and how circadian rhythm changes adversely affect medical flight crew members as measured by complaints.
q 4 or more Methods
13) How
does
your
program
employ?
Thank You for Completing
middle of a designated rest/sleep period and very sleepy during active flight periods.7 Decrements in vigilance and alertness result from disrupted sleep patterns. Sleep deprivation slows the performance of challenging intellectual tasks; however, motivation to perform routine tasks is diminished. Sleepdeprived subjects have more errors of omission in work-paced tasks (e.g., monitoring, telemetry, suturing), whereas in self-paced tasks (e.g., 84
This Survey
problem solving) speed is impaired but accuracy remains high. Emergency medical professionals clearly must perform both of these types of tasks.2 Mood swings and increased rates of divorce are associatedwith changes in circadian rhythm.2257 Other problem areas include gastrointestinal dysfunction, infertility,3,5-7 and, most importantly to air medical transport, increased rates of errors and on-the-job injuries. These in-
A B-question survey was developed and sent to the chief flight nurses of 123 rotorwing-only Association of Air Medical Servicesmembers as taken from the 1992 AAMS Membership Directory. The survey was sent to rotor-wing-only programs to alleviate the problems associated with fixed-wing scheduling (on call, long flight times, etc.). Survey questions focused on scheduling strategies and comments/ complaints that speciticallytargeted circadian rhythm changes in relation to rotating shifts (Figure 1). Results
Of the 123 surveys sent, 98 were re14:2
April-June
1995
Air Medical
Journal
turned resulting in an 80% response rate. Of the programs responding, 55% of the medical flight crew members (FCM) rotate shifts, while 45%do not rotate shifts. Of those that do rotate shifts, 36% of programs take into account the circadian rhythm of FCMs when making the schedule, while the remaining 64% of the programs do not take circadian rhythm into account. Of the crews that do not rotate, 45% work 24-hour shifts, while the remaining 55%work a permanent shift. The comments and complaints of those programs that used rotating shiis were compiled and grouped into similar categories. These comments and complaints were further sorted into whether or not circadian rhythm is taken into account when making the schedule (Table 1). Sleep deprivation was by far the largest response. Of the complaints, 67% came from programs that do not take circadian rhythm into account (which was expected), while the remaining 33% of the complaints came from programs stating that they do take circadian rhythm into account when making the schedule. Of those programs in which fatigue was a major complaint, 60%came from the programs that stated that they do take circadian rhythm into account when making the schedule. Other complaints included disruption of family lifestyle and meal patterns, “hating nights” and trouble adjusting to the night rotation. Discussion
Circadian rhythm is not taken into account in the majority of programs with rotating schedules, and two-thirds of these programs report sleep deprivation/disorder twice as often as those programs with rotating schedules that do consider circadian rhythm. Therefore, it would appear that considering circadian rhythm in scheduling rotating shifts can cut complaints (and potentially mistakes, accidents and injuries) in half. Other complaints and adverse effects were distributed equally between those programs that considered circadian rhythm and those that did not. Therefore, additional measures other than simply considering circadian rhythm are necessary. For example, “trouble adjustAir Medical
Journal
14:2
April-June
1995
Comments and Complaints of Those Who Work a Rotating Schedule Programs Rhythms
in Which is Taken
Circadian into Account
Programs Rhythms
in Which Circadian is Not Taken into Account
33% - Sleep deprivation/ disorder
67%
- Sleep
deprivation
-
80%
- “Hating
nights”
60%
- Fatigue
80% - Disruption of family and meal patterns 60%
/disorder
- Trouble
adjusting
lifestyle
to nights
ing to nights” was reported with equal frequency, and might be addressed by increasing the length of the rotation schedule.2~7~10A program currently on a two-weeks-of-days/two-weeks-of-nights rotation might try a four-week/fourweek cycle. There are suggestions of other solutions within the survey. For example, programs that work 24-hour shifts reported less stress and higher morale. Such shifts have been associated with decreased turnover costs, orientation and overtime expenses, personal stress and burnout.11 While this solution is not suitable for all situations, it might be considered where there are low tlight volumes and few, if any, ancillary duties. Twentyfour hours shifts have their own possible difficulties, including longer periods of time spent away from family and friends, and higher stress due to flying more critical patients in a shift. The study was limited in that the r-e spondents were the chief flight nurses of each program rather than the nurses and paramedics themselves. Many chief flight nurses work a regular, daytime schedule, and, thus, the information obtained was based on reports by medical crew members. Future studies should include discussions with medical crew members themselves, as well as standard definitions of the complaints. Additionally, fixed-wing programs also should be sampled. It is possible to induce complete physiologic adaptation by exposure to bright light at night and “dark” dark during the
80% - Disruption of family and meal patterns 60%
- Trouble
adjusting
lifestyle
to nights
day. Exposure to four appropriately designed cycles of 7000 to 12,000 lux, comparable to natural sunlight at dawn, can induce a complete physiologic adaptation to night.5 Such a regimen counteracts the environmental clues received during travel to and from work. Unfortunately, such a regimen is diicult to achieve in practice. First, such bright light is not readily available to the average worker.3 Additionally, working the night shift with time spent in the emergency department (average room lighting equals 150 lux) interrupted by a flight at 0300 results in contradictory clues. Common sense also can contribute to physiologic adaptation to a rotating schedule. Careful scheduling of social activities can minimize conflicting environmental time clues. For example, playing soccer at noon in the middle of four consecutive night shiis most certainly will counteract any adaptation that has taken place. Conclusion
This study points out the difficulties asso ciated with rotating shifts. The consideration of circadian rhythm in the assignment of shifts will ameliorate some of the problems, but other measures are necessary and beneficial. Acknowledgments
The author thanks Vi&i Sykora, RN, for her help in the initial stages of this work. The author also thanks ST Martin, BS, and SD Black, PhD, for the technical assistance given during the writing of the manuscript. 85
References 1. Johnson BC: Nutrient intake as a time signal for circadian rhythm./Nutr 1992;122:1753-1759 2. Whitehead DC, Thomas H, Slapper DR: A rational approach to shift work in emergency medicine. Ann Emerg Med 1992;21:1250-1258. 3. Winfree AT: Resettting the human clock. Nature 1991;350:18. 4. Hastings JW, Czeisler CA: Day-night differences are not always due to circadian control. Ann EmergMed 1992;21:1236 5. Czeisler CA, Johnson MP, Duffy JF, et al: Expo
86
sure to bright liiht and darkness to treat physio logic maladaption to night work. N Engl J Med 1990;322:1253-1259. 6. Cauter EV, Turek Fw: Strategies for resetting the human circadian clock. N Engl J Med 1990;322:1306-1308. 7. Carthome CV, Fedorowicz RJ: Work/rest schedules and their potential impact on flight crew performance. Hospital Aviation 1985;3:5-7. 8. Glazner LK: Shiftwork: Its effect on workers. AAOHNJoloumzal1991;39:41&421.
9.
Gold DR, Rogacz S, Bock N, et al: Rotating shift work, sleep and accidents related to sleepiness in hospital nurses. Am J Public Health 1992; 82:1011-1013. 10. Siebenaler MJ, McGovern PM: Shiftworkconsequences and considerations. AAOHN Journal 1990;39:558-567. 11. Capoazi S, Glahn S, Phan P: A 24hour shift op tion in level one trauma ORs. Nursing Management 1990;21:96Y-962.
Air Medical
Journal
14:2
April-June
1995
Adverse Effects of Rotating Schedules on the Circadian Rhythms of Air Medical Crews Timothy C. Martin, BS, NREMT-P1 1.
Flight For Life, Mother Tyler, Texas
Key Words: aeromedical, sleep deprivation
Frances
Hospital,
circadian
rhythm,
Address for correspondence: NREMT-P, 13121 Southview TX 75240;TCM692@aol,com
T.C. Martin, BS Lane, Dallas,
Submitted: November 7,1994 Revised: April 20, 1995 Accepted: May 1, 1995 This paper was presented at the 14th Annual Air Medical Transpori Conference in St. Louis, MO., on October 4, 1993.
Air Medical
Journal
14:2
April-June
1995
Introduction Observations of the rhythmic nature of animal behavior date back to the time of Aristotle, who noted swelling of sea urchin ovaries during the full moon.1 “Sleep movements” of plants also were noted by the ancient Greeks, who attributed the phenomena to the presence or absence of sunlight. Circadian rhythm (Latin: circa meaning about, and diem meaning a day) is defined as an inborn, genetically programmed, self-sustained rhythm in behavior, physiology and metabolism, developed over evolutionary time that enables living organisms to cope with the 24hour daily rotation of the planet.’ One of the first experiments designed to test circadian rhythms in plants was done in 1729 by de Mairan, who illustrated that plant leaves open in the daytime even when kept in total darkness.2 This was the first presentation of evidence of an endogenous biological clock that functioned in the absence of zeitgebers (German for “time givers” or clues to the time of day). The term “free running” has been used to describe a rhythm in behavior pattern, or resultant metabolic pattern, that continues in the absence of any exogenous clues.1 The concept of freerunning biological clocks was discovered in 1832 by de Candolle, who placed plants in constant bright light.2 After a few days, the leaves opened and closed on a 22-hour cycle. This display indicated that the plant had its own independent day length. Circadian rhythms have endogenous and exogenous components; the former is dependent on a clocklike
mechanism, while the latter is driven by external time clues (zeitgebers).zThe endogenous clock appears to be responsible for the free-running day length, and light/dark cycles have been shown to be important in adjusting the human circadian clock. Many species of invertebrates demonstrate that circadian clocks have evolved mechanisms by which they frequently are reset to keep pace with changes in the local environment, most notably by being sensitive to the intensity of light.3 Controlled experiments have shown that humans have a 25.1-hour circadian clock that is constant and predictable but entrained to the 24-hour day by environmental clues.294Volunteers were studied by Weitzman and Czeisler in periods ranging from two weeks to six months, during which they were isolated from any zeitgebers. Subjects were permitted to eat and sleep at times of their own choosing, and after one week in the clue-free environment, they lagged behind their usual day/night schedules by almost eight hours. This implies that human internal clocks are reset on a daily basis.2 Forced changes in circadian rhythm produce sleep disruption and deprivation.2,5-7The circadian system influences performance through its effects on metabolic functions and on quality of sleep. Its rhythmicity and consistency is crucial to the maintenance of normal levels of body function and performance. The most obvious change occurs in sleep patterns, where sleep becomes shortened and disrupted by the displacement of the circadian rhythm. Pilots undergoing a shift change may find themselves awake in the a3
Circadian Rhythm and Shift Schedule Survey 1) How
many 08
Please
hours
a day are your flight crew members 0 12 0 24 0 Other-Please
fill in the average Sun
Mon
two-week
Tues
shift of a full-time
Wed
Thurs
Fri
(FCMs) scheduled explain FCM.
FCMs
have
a permanent
q Y
a check
or an x).
Sat
2) Do your FCMs have a permanent shift (e.g., permanent N Y 0 Permanent evenings 0 Permanent days 3) Do your
(With
to work?
days,
etc.)?
0 Permanent
nights
partner?
ON
4) Do your FCMs rotate shifts (e.g., days, Y N 0 Days => Evenings => Nights 0 Days => Nights
evenings,
nights
or days/nights)?
5) If FCMs do rotate shifts, how long do the rotations last? 0 2 Weeks 0 4 Weeks 0 6 Weeks 0 Other-Please 6) How
long does it take for the average Days => nights Nights => days Not Applicable
7) What
is the biggest
complaint
your
FCM to adapt
FCMs
have about
6a) Does your program permit FCMs to sleep? 0 Y q N take
10) What do you think the ideal shift schedule A) For personnel? B) For your program? many
flights
12) How
many 01
aircraft
many
FCMs
per month does 02
rotating
rotating
from:
shifts?
b) If not, is there a place for them to “relax”? 0 Y 0 N
9) Does your program’s shift scheduling 0 Y q N If yes, please explain:
11) How
explain
does
your
your program 03
into account
the FCMs
circadian
rhythm?
is:
program
average?
utilize?
juries appear to occur more frequently at certain times of the day because worker performance is affected by disruptions in the circadian rhythm.8 One study found that most injuries in shift workers occurred between 10 p.m. and 2 a.m. and that firefighters sustain more injuries during the night shift.8 A hospital-based survey on &ii work, sleep and accidents was carried out among 635 Massachusetts nurses.9 In comparison to nurses who only worked day or evening shifts, nurses who rotated shifts had more sleep/wake cycle disrup tion and nodded off more at work.9 The rotating nurses had twice the odds of nodding off while driving to or from work, and twice the odds of a reported accident or error related to sleepiness.9 People who have worked nights for several years continue to complain of fatigue and trouble adjusting.6 This is because the body is exposed to contlicting synchronizing clues: the work schedule demands activity at night and sleep during the day, whereas all other environmental and social clues point to activity during the day and sleep at night.5 Animal models suggest diminished longevity as a consequence of rotating shifts, and in Japan there is legal precedent for considering night work a compensable cause of premature death.2 The purpose of this study was to ascertain how many programs use a rotating schedule and how circadian rhythm changes adversely affect medical flight crew members as measured by complaints.
q 4 or more Methods
13) How
does
your
program
employ?
Thank You for Completing
middle of a designated rest/sleep period and very sleepy during active flight periods.7 Decrements in vigilance and alertness result from disrupted sleep patterns. Sleep deprivation slows the performance of challenging intellectual tasks; however, motivation to perform routine tasks is diminished. Sleepdeprived subjects have more errors of omission in work-paced tasks (e.g., monitoring, telemetry, suturing), whereas in self-paced tasks (e.g., 84
This Survey
problem solving) speed is impaired but accuracy remains high. Emergency medical professionals clearly must perform both of these types of tasks.2 Mood swings and increased rates of divorce are associatedwith changes in circadian rhythm.2257 Other problem areas include gastrointestinal dysfunction, infertility,3,5-7 and, most importantly to air medical transport, increased rates of errors and on-the-job injuries. These in-
A B-question survey was developed and sent to the chief flight nurses of 123 rotorwing-only Association of Air Medical Servicesmembers as taken from the 1992 AAMS Membership Directory. The survey was sent to rotor-wing-only programs to alleviate the problems associated with fixed-wing scheduling (on call, long flight times, etc.). Survey questions focused on scheduling strategies and comments/ complaints that speciticallytargeted circadian rhythm changes in relation to rotating shifts (Figure 1). Results
Of the 123 surveys sent, 98 were re14:2
April-June
1995
Air Medical
Journal
turned resulting in an 80% response rate. Of the programs responding, 55% of the medical flight crew members (FCM) rotate shifts, while 45%do not rotate shifts. Of those that do rotate shifts, 36% of programs take into account the circadian rhythm of FCMs when making the schedule, while the remaining 64% of the programs do not take circadian rhythm into account. Of the crews that do not rotate, 45% work 24-hour shifts, while the remaining 55%work a permanent shift. The comments and complaints of those programs that used rotating shiis were compiled and grouped into similar categories. These comments and complaints were further sorted into whether or not circadian rhythm is taken into account when making the schedule (Table 1). Sleep deprivation was by far the largest response. Of the complaints, 67% came from programs that do not take circadian rhythm into account (which was expected), while the remaining 33% of the complaints came from programs stating that they do take circadian rhythm into account when making the schedule. Of those programs in which fatigue was a major complaint, 60%came from the programs that stated that they do take circadian rhythm into account when making the schedule. Other complaints included disruption of family lifestyle and meal patterns, “hating nights” and trouble adjusting to the night rotation. Discussion
Circadian rhythm is not taken into account in the majority of programs with rotating schedules, and two-thirds of these programs report sleep deprivation/disorder twice as often as those programs with rotating schedules that do consider circadian rhythm. Therefore, it would appear that considering circadian rhythm in scheduling rotating shifts can cut complaints (and potentially mistakes, accidents and injuries) in half. Other complaints and adverse effects were distributed equally between those programs that considered circadian rhythm and those that did not. Therefore, additional measures other than simply considering circadian rhythm are necessary. For example, “trouble adjustAir Medical
Journal
14:2
April-June
1995
Comments and Complaints of Those Who Work a Rotating Schedule Programs Rhythms
in Which is Taken
Circadian into Account
Programs Rhythms
in Which Circadian is Not Taken into Account
33% - Sleep deprivation/ disorder
67%
- Sleep
deprivation
-
80%
- “Hating
nights”
60%
- Fatigue
80% - Disruption of family and meal patterns 60%
/disorder
- Trouble
adjusting
lifestyle
to nights
ing to nights” was reported with equal frequency, and might be addressed by increasing the length of the rotation schedule.2~7~10A program currently on a two-weeks-of-days/two-weeks-of-nights rotation might try a four-week/fourweek cycle. There are suggestions of other solutions within the survey. For example, programs that work 24-hour shifts reported less stress and higher morale. Such shifts have been associated with decreased turnover costs, orientation and overtime expenses, personal stress and burnout.11 While this solution is not suitable for all situations, it might be considered where there are low tlight volumes and few, if any, ancillary duties. Twentyfour hours shifts have their own possible difficulties, including longer periods of time spent away from family and friends, and higher stress due to flying more critical patients in a shift. The study was limited in that the r-e spondents were the chief flight nurses of each program rather than the nurses and paramedics themselves. Many chief flight nurses work a regular, daytime schedule, and, thus, the information obtained was based on reports by medical crew members. Future studies should include discussions with medical crew members themselves, as well as standard definitions of the complaints. Additionally, fixed-wing programs also should be sampled. It is possible to induce complete physiologic adaptation by exposure to bright light at night and “dark” dark during the
80% - Disruption of family and meal patterns 60%
- Trouble
adjusting
lifestyle
to nights
day. Exposure to four appropriately designed cycles of 7000 to 12,000 lux, comparable to natural sunlight at dawn, can induce a complete physiologic adaptation to night.5 Such a regimen counteracts the environmental clues received during travel to and from work. Unfortunately, such a regimen is diicult to achieve in practice. First, such bright light is not readily available to the average worker.3 Additionally, working the night shift with time spent in the emergency department (average room lighting equals 150 lux) interrupted by a flight at 0300 results in contradictory clues. Common sense also can contribute to physiologic adaptation to a rotating schedule. Careful scheduling of social activities can minimize conflicting environmental time clues. For example, playing soccer at noon in the middle of four consecutive night shiis most certainly will counteract any adaptation that has taken place. Conclusion
This study points out the difficulties asso ciated with rotating shifts. The consideration of circadian rhythm in the assignment of shifts will ameliorate some of the problems, but other measures are necessary and beneficial. Acknowledgments
The author thanks Vi&i Sykora, RN, for her help in the initial stages of this work. The author also thanks ST Martin, BS, and SD Black, PhD, for the technical assistance given during the writing of the manuscript. 85
References 1. Johnson BC: Nutrient intake as a time signal for circadian rhythm./Nutr 1992;122:1753-1759 2. Whitehead DC, Thomas H, Slapper DR: A rational approach to shift work in emergency medicine. Ann Emerg Med 1992;21:1250-1258. 3. Winfree AT: Resettting the human clock. Nature 1991;350:18. 4. Hastings JW, Czeisler CA: Day-night differences are not always due to circadian control. Ann EmergMed 1992;21:1236 5. Czeisler CA, Johnson MP, Duffy JF, et al: Expo
86
sure to bright liiht and darkness to treat physio logic maladaption to night work. N Engl J Med 1990;322:1253-1259. 6. Cauter EV, Turek Fw: Strategies for resetting the human circadian clock. N Engl J Med 1990;322:1306-1308. 7. Carthome CV, Fedorowicz RJ: Work/rest schedules and their potential impact on flight crew performance. Hospital Aviation 1985;3:5-7. 8. Glazner LK: Shiftwork: Its effect on workers. AAOHNJoloumzal1991;39:41&421.
9.
Gold DR, Rogacz S, Bock N, et al: Rotating shift work, sleep and accidents related to sleepiness in hospital nurses. Am J Public Health 1992; 82:1011-1013. 10. Siebenaler MJ, McGovern PM: Shiftworkconsequences and considerations. AAOHN Journal 1990;39:558-567. 11. Capoazi S, Glahn S, Phan P: A 24hour shift op tion in level one trauma ORs. Nursing Management 1990;21:96Y-962.
Air Medical
Journal
14:2
April-June
1995