Air travel and seizure frequency for individuals with epilepsy

Open ArchivePublished:May 01, 2006DOI:https://doi.org/10.1016/j.seizure.2006.03.006

      Summary

      This study investigated whether air travel is associated with an increase in seizures for individuals with epilepsy. Thirty-seven participants monitored their seizure frequency for one week prior to flying and for one week after flying. For the sample as a whole, seizures were significantly more common after flying (p = .02). No seizures were reported as occurring during flight. Participants who experienced an increase in seizures after flying compared to those who did not (a) had a higher baseline of seizure frequency (p = .004), (b) were more likely to have previously experienced an increase in seizures after flying (p = .001), (c) were more worried about having a seizure while flying (p = .001) and (d) were more likely to avoid air travel (p = .02). Participants with complete seizure control prior to flying did not experience seizures after flying. Distance traveled, time zones crossed, duration of flight and direction of flight were not significantly different for those with seizure increase than for those without such an increase. This study suggests that air travel promotes an increase in seizures for those with a prior history of flight related seizures and a relatively high baseline seizure frequency.

      Keywords

      Introduction

      Most concern regarding passenger welfare during air travel tends to focus on issues of air safety, such as pilot error and incapacitation, catastrophic accidents, and terrorism. Consideration is also given to the role air travel may play in causing and exacerbating medical conditions.
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      The effects of flying: processes, consequences and prevention.
      The cabin of a commercial airliner in flight presents a number of physiological challenges. The typical commercial flight cruises between 28,000 and 43,000 ft
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      Air travel and patients with pulmonary and allergic conditions.
      and atmospheric pressure inside the cabin is reduced 15–18% as compared to sea-level.
      • Berg B.W.
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      Hypoxemia during air travel.
      • Monaghan A.M.
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      At such altitudes the rate at which oxygen can diffuse into the blood is decreased.
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      Physiology for nursing practice.
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      The humidity in an air cabin is kept low (8–12%)
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      Assuring safe travel for today's elderly.
      and exposure to cosmic radiation is about 100% greater than at sea level.
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      In addition, passengers’ postural mobility in most cabin settings is greatly restricted. As such, most air travelers are exposed to cramped, dry, hypobaric and hypoxic environments, with high levels of cosmic radiation.
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      The vast majority of travelers adequately tolerate in-flight physiological challenges. However, air travel contributes to the development of a number of serious health problems particularly for specific at-risk populations. For example, air travel appears to put passengers at greater risk for deep vein thrombosis (DVT) and pulmonary embolism, particularly for passengers with a previous history of DVT.
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      Deep vein thrombosis (DVT) a small risk after air travel.
      Passengers with chronic obstructive pulmonary disease and smokers are at increased risk of hypoxemia.
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      Medical problems have been linked to those who fly most, for example, increased cancer rates among flight attendants,
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      , and developing nuclear cataracts in pilots.
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      Cosmic radiation increases the risk of nuclear cataract in airline pilots: a population-based case-control study.
      To avoid potential fetal injury due to radiation women are cautioned against flying more than 200 h during the course of a pregnancy.

      International Commission on Radiological Protection, ICRP Publication 84: Pregnancy and medical radiation, Pergamon Press, 2000.

      Less threatening and more transient health effects of air travel include pain from gas exchanges, such as earaches, sinus pressure, and abdominal cramping. Passengers that cross several time zones are also subject to the common experience of jet lag.
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      Jet-lag.
      It appears that no study to date has investigated the effects of air travel on individuals with epilepsy. There are a number of reasons why such studies are warranted. If air travel promotes seizures, there is the potential for vast numbers of individuals with epilepsy to be affected. Several flight-related physiological challenges (for example, sleep deprivation, oxygen desaturation) may lower seizure threshold (described below). The relative risk of passengers with epilepsy having a seizure either during or after flying has not been established. Such information would be helpful in formulating air carrier policies and procedures for managing passengers with epilepsy. It would also help physicians’ clinical management of patients with epilepsy who are intending to travel by air.
      While there are no published estimates of how many people with epilepsy travel by air, the number of individuals affected is likely to be considerable. In 2003, over 646 million revenue passengers enplaned in the US.

      U.S. Bureau of Transportation Statistics Annual Report, 2004. Retrieved 15 August 2005 from www.bts.gov.

      An estimation based on a crude prevalence rate for epilepsy of 6.42 per 1000
      • Hauser W.A.
      • Hesdoffer D.C.
      Epilepsy: frequency, causes and consequences.
      suggests that in 2003, individuals with epilepsy enplaned in the US over 4 million times. This frequency of air travel may be an overestimation, as individuals with epilepsy are less likely to fly due to financial limitations and concerns about air travel.

      International Bureau for Epilepsy. Problems with flying? Retrieved 5 May 2004 from http://www.ibe-epilepsy.org.

      U.S. Department of Transportation, Bureau of Transportation Statistics. 1995 American Travel Survey, BTS/ATS95-US, October 1997.

      Nevertheless, air travel has the potential of affecting millions of individuals with epilepsy.
      If air travel does lower seizure threshold it may do so through causing sleep disruption and sleep loss.
      • Nicholson A.N.
      Duty hours and sleep patterns in aircrews operation world-wide routes.
      • Winget C.M.
      • DeRoshia C.W.
      • Markley C.L.
      • Holly D.C.
      A review of human physiological and performance changes associated with desynchronosis of biological rhythms.
      For many individuals with epilepsy, seizures appear more likely around fluctuations of consciousness associated with sleep, such as the brief period of falling asleep,
      • Wyler A.R.
      Epileptic neurons during sleep and wakefulness.
      momentary awakenings,
      • Niedermeyer E.
      The generalized epilepsies.
      and awakening in the morning while still drowsy.
      • Biniaurishvili R.G.
      • Yakhno N.N.
      Electroencephalographic features of sleep in epilepsy.
      Telemonitored observations also indicate that seizures tend to be concentrated around fluctuations of consciousness.
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      A study of the distribution of the petit mal absences in the child in relation to his activities.
      • Neill J.C.
      • Alvarez N.
      The effects of everyday environment on epileptic activity in three mentally retarded individuals.
      Prolonged air travel in a fixed environment with restricted movement and a limited range of activities, may promote drowsiness and periods of reduced cortical activation. Sleep rhythms may be disrupted for several days after flying, particularly with extended flights. Eastward air travel is particularly disruptive to sleep schedules.
      • Graeber R.C.
      Alterations in performance following rapid transmeridian flight.
      The number of days required for a traveler to return to pre-flight sleep patterns is about one day for each 90 min travel westward compared to one day per 60 min travel eastward.
      • Herxheimer A.
      Coping with jetlag.
      Another means by which air travel may lower seizure threshold is through the effect of air cabin oxygen desaturation. As previously noted, at high altitudes the rate at which oxygen can diffuse into the blood is diminished.
      • Hinchliff S.M.
      • Montague S.F.
      • Watson R.
      Physiology for nursing practice.
      While most travelers tolerate prolonged exposure to decreased ambient oxygen during flight, individuals with epilepsy may be at risk. Lower inspired oxygen during flight may trigger compensatory hyperventilation.
      • Bettes T.N.
      • McKenas D.K.
      Medical advice for commercial air travelers.
      Fried
      • Fried R.
      Breathing training for the self-regulation of alveolar CO2 in the behavioral control of idiopathic epileptic seizures.
      argues that seizures can result from metabolic instability created by hyperventilation. The resultant decreased carbon dioxide intake results in reduced cerebral blood flow and oxygen supply to the brain. In addition, hyperventilation increases blood pH (alkalosis), which makes oxygen less likely to be released to tissues.
      • Woodson R.D.
      Physiological significance of the oxygen dissociation curve shift.
      Hyperventilation has long been known to induce seizures for those with idiopathic epilepsy
      • Lennox W.G.
      The effect of epileptic seizures of varying the composition of inspired air.
      • Rosett J.
      The experimental production of rigidity, or abnormal involuntary movement and abnormal states of consciousness in man.
      and controlled breathing can result in reduced seizure frequency.
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      Measurement of tissue PCO2 in the brain.
      • Fried R.
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      • Fox M.C.
      Behavioral control of intractable idiopathic seizures. I. Self-regulation of end-tidal carbon dioxide.
      • Fried R.
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      • Carlton R.M.
      Effect of diaphramatic respiration with end-tidal CO2 biofeedback on respiration, EEG, and seizure frequency in idiopathic epilepsy.
      The likelihood that a person with epilepsy will have a seizure while flying has not been established. It is difficult to determine the incidence of any in-flight medical emergency as airlines are not required to report them.
      • Drummond R.
      • Drummond A.
      On a wing and a prayer: medical emergencies on board commercial aircraft.
      The studies that have been done report the frequency of neurological events but seldom report the incidence of seizures per se. Neurological events range from 4 to 12% of all in-flight medical emergencies (reviewed by DeJohn et al.
      • DeJohn C.A.
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      • Smith D.W.
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      The evaluation of in-flight medical care aboard selected. U.S. air carriers: 1996–1997.
      ) and presumably a good portion of those events are seizures. In a prospective survey of Seattle-Tacoma International Airport, Cummins and Schuhbach
      • Cummins R.O.
      • Schubach J.A.
      Frequency and types of medical emergencies among commercial air travelers.
      found that in-flight medical emergencies occur for about one of every 39,000 passengers and that about 6% of these were seizures.
      The inability to adequately manage a seizure in flight has serious health and financial consequences. While most seizures resolve without the need for medical intervention, an episode of generalized convulsive status epilepticus may result in irreversible neuronal injury and death; prognosis depending on the time between the onset of the seizure and the start of effective treatment.
      • Manno E.M.
      New management strategies in the treatment of status epilepticus.
      • Treiman D.M.
      Therapy of status epilepticus in adults and children.
      A passenger experiencing a partial-complex seizure may be considered intentionally disruptive or even dangerous, particularly in this post-911 environment. Whether for medical and/or safety concerns, an onboard seizure may result in the flight crews’ decision to have an unscheduled landing. Such diversions are more likely to be the result of neurological events than most other medical events. DeJohn et al.
      • DeJohn C.A.
      • Veronneau S.J.H.
      • Wolbrink A.M.
      • Larcher J.G.
      • Smith D.W.
      • Garett J.
      The evaluation of in-flight medical care aboard selected. U.S. air carriers: 1996–1997.
      found that neurological events were the second leading cause of flight diversions after cardiac events (18 and 45.5%, respectively).
      There are no guidelines for identifying patients at risk for an increase in seizures due to air travel and such information would be helpful to physicians and air carriers. Physicians would be able to inform patients as to the type and degree of risk they are taking by flying and determine strategies, as warranted, to increase seizure threshold during travel. Bettes and McKenas
      • Bettes T.N.
      • McKenas D.K.
      Medical advice for commercial air travelers.
      suggest that patients with epilepsy consider a temporary, small increase in anticonvulsant medication during air travel, although they do not report how this recommendation was determined. Data on the relative risk of flying would assist air carrier personnel in making decisions regarding who is appropriate to fly and what resources are required to meet the needs of passengers with epilepsy. In the US, it is illegal for carriers to deny a person access to a flight based on a medical diagnosis unless it is established that there is a legitimate safety risk.

      U.S. Department of Transportation, Office of Aviation Enforcement and Proceedings. Nondiscrimination on the basis of disability in air travel, 14 CFR Part 382.31, May 2001. Retrieved 28 July 2004 from http://airconsumer.ost.dot.gov/rules.

      This position has been heralded as progress towards establishing the rights of persons with disabilities to travel free of discrimination.

      International Bureau for Epilepsy. Problems with flying? Retrieved 5 May 2004 from http://www.ibe-epilepsy.org.

      However, criteria as to what would constitute a safety risk for individuals with epilepsy who intend to fly have not been established. The current Aerospace Medical Association guidelines
      • Alvarez D.X.
      • Bagshaw M.
      • Cambell M.
      • Davis J.R.
      • et al.
      Medical guidelines for airline travel.
      state that “most patients with epilepsy can fly safely” (p. 13) but the empirical basis of this position has not been presented and there is no apparent consideration of possible problems after air travel.
      This study begins to address unanswered questions as to the effect of flight on epilepsy. First, does air travel promote an increase in seizures? Second, if seizures are more common after flying than before, who appears most vulnerable for such an increase? Finally, what kinds of flight characteristics appear to promote an increase in seizures?
      It was hypothesized that air travel is associated with an increase in seizures and that those with poorly controlled epilepsy would be more likely to experience an increase in seizures after flying. Also considered was the length and direction of flight. It was hypothesized that post flight seizure increase would be associated with greater distance traveled, and with eastbound transmeridian travel.

      Methods

       Participants

      Recruitment occurred through neurologists’ offices, epilepsy organizations, and epilepsy conferences. Prospective participants were informed of the requirements for participation, which included completing a questionnaire and prospectively monitoring their seizure frequency for a 15-day period. Participation was voluntary, and the flights were taken for personal and business reasons unrelated to the study. Participants did not receive compensation for being in the study. The study was reviewed and accepted by an internal review board of the author's institution, and participants (and in one case a participant's parents) completed informed consent forms. Selection criteria included (a) a diagnosis of epilepsy, (b) the ability to prospectively self-monitor seizures seven days before and after flying, and (c) not taking additional flights during the “post-flight” week. Participants who took more than one flight en route to a destination (connecting flights) were also included in the study.
      Forty-five prospective participants completed the questionnaire and self-monitoring form. From this pool, eight were rejected because participants did not prospectively self-monitor seizures, provide flight information, or monitor post-flight seizures (n = 37 participants).

       Measures

      Participants completed a questionnaire, developed by the author that addressed epilepsy history, medication use, prior experiences with air travel, and details of the flight taken for the study. Participants were asked to monitor their seizures on a daily basis for seven days prior to the flight, for the day of the flight, and for seven days after the flight. The data collection period was determined because studies of extended flight indicate that an individual's physiological and subjective symptoms of jet lag, such as sleep disruption, take as much as a week to return to pre-flight status.
      • Buck A.
      • Tobler I.
      • Borbely A.A.
      Wrist activity monitoring in aircrew members: a method for analyzing sleep quality following transmeridian and north-south flights.
      Completed questionnaires were mailed to the author who made follow-up telephone contact with participants, when possible, to clarify and confirm responses made on the questionnaire.

      Results

       Data analysis

      Descriptive statistics were computed for subject demographics, seizure frequency, flight history and flight related variables. Distributions of continuous variables were assessed for normality (Kolmogorov–Smirnov test). Where normality of the data could not be established, non-parametric approaches to the data were taken.
      A comparison of participants with post-flight seizure increase, heretofore referred to as “increasers,” with those without post-flight increase “non-increasers” was done using Students’ t-test for (a) flights taken last year, (b) distance flown, (c) distance flown per east and west direction of flight, (d) time zones crossed, and (e) duration of flight. Students’ t-test was also used to compare pre-and post-flight seizure frequency. Chi-square analysis was used to compare increasers versus non-increasers in terms of baseline seizure frequency, history of previous flight-related seizures, worry regarding flight related seizure, avoidance of flying, and flight direction.

       Participant characteristics

      A majority of the 37 participants were female (26), in their thirties (mean age 38 years), Caucasian (30), well educated (30 college educated) and employed (67%). A nine-year-old boy participated in the study, and his parents monitored his seizures and completed the questionnaire. Participants’ seizure information is reported in Table 1. Most participants reported having generalized or generalized and partial seizures. Slightly over half were taking a single anticonvulsant and another third were taking two anticonvulsants. Only one participant reported changing the amount of anticonvulsant during the study, increasing her dose during the post flight week. Most participants reported having good control over their seizures; over half of the participants reported having less than one seizure per month prior to involvement in the study. The most commonly reported triggers for seizures were being short on sleep (75%) and stress (70%). The only patient characteristic that differentiated non-increasers from increasers was that baseline seizure frequency was higher for increasers (described below).
      Table 1Participants’ epilepsy characteristics
      All (n = 37)Non-increasers (n = 27)Increasers (n = 10)
      Seizure type
       Partial only321
       Generalized only22166
       Partial and generalized1293
       Experience auras18117
      Seizure rate (month) (prior to study)
       No seizures10100
       Mean seizure
      Computed after removal of outlier with 55 seizures per month.
      1.771.073.77
      p=.004.
       Range0–110–8.5–11
      a Computed after removal of outlier with 55 seizures per month.
      ** p = .004.

       Flight history

      Participants were generally familiar with air travel (see Table 2). Ten participants reported having taken more than 50 flights, and only six participants reported taking less than 10 flights. Increasers did not report taking fewer flights. Almost half of all participants reported having noticed an increase in their seizures after flying. Increasers were more likely than non-increasers to report having a prior history of post-flight seizure increase (X2 = 10.33, d.f. = 1, N = 32, p = .001), to report being worried about having a flight related seizure (X2 = 10.35, d.f. = 1, N = 37, p = .001), and to avoid flying (X2 = 5.23, d.f. = 1, N = 37, p = .02). All participants who did not have a history of flight related seizure increases avoided an increase in seizures during this study.
      Table 2Participants’ flight history and flight characteristics
      All (n = 37)No increasers (n = 27)Increasers (n = 10)
      Flights since first seizure (n = 34)
       0–10660
       11–5018126
       51–100532
       101–500431
       501–1000110
      Mean flights last year8.478.967.20
      History flight-related seizures
       Yes1688
      p=.001.
       No16160
       No response050302
      Worry seizure in flight
       Yes1147
      p=.001.
       No26233
      Avoid flying
       Yes413
      p=.022.
       No33267
      Mean distance (miles)241321603094
      Flight direction
       East1394
       West17143
       North/south743
       Time-zones mean2.812.663.20
      * p = .001.
      ** p = .022.

       Study flight

      The mean flight distance over 2400 miles and lasted for approximately 6 h (see Table 2). This distance is greater than the median flight taken in the U.S. of 1732 miles.

      U.S. Department of Transportation, Bureau of Transportation Statistics. 1995 American Travel Survey, BTS/ATS95-US, October 1997.

      Distance traveled, the number of time zones crossed, and the duration of travel was greater, although not significantly so, for increasers versus non-increasers. Increasers were no more likely to travel in a particular direction or travel further in a particular direction than non-increasers.

       Study seizure frequency

      No participant reported having a seizure while flying. Twenty-three of the 37 participants did not have seizures before or after flying. Of the remaining 14 participants, 10 had more seizures after flying, one had the same number of seizures, and three reported a decrease in post-flight seizure frequency (see Fig. 1). It should be noted that one of the three participants, who reported a decrease in seizure frequency after flying, increased the dosage of her anticonvulsant medication for the week after taking the flight. This participant had a baseline seizure rate of 8 seizures per month.
      Figure thumbnail gr1
      Figure 1Sum of seizures per day (participants’ flight taken during day eight).
      The mean number of seizures per day for the post-flight week almost doubled (t = 2.47, d.f. = 13, p = .02) (see Fig. 1). Three participants’ post-flight seizure increase was particularly striking with increases of 13, 16, and 30 seizures. Of the increasers, four reported both generalized and partial seizures, four had only generalized seizures, one had only partial seizures, and one reported having absence seizures.
      A trend was noted for increasers being more likely to experience seizures the week before flying (X2 = 3.31, d.f. = 1, N = 37, p = .06). Four of the increasers had seizures the week before flying compared to only 3 of the 27 non-increasers.

       Baseline seizure frequency

      Baseline seizure frequency related significantly to post-flight seizure increase (X2 = 8.13, d.f. = 1, N = 34, p = .004). Increasers had a higher rate of seizures before flying (i.e., mean of 3.77 per month) than non-increasers (i.e., mean of 1.07 per month). None of the 10 participants who reported complete control over seizures prior to participation with the study had seizures after flying.

      Discussion

      In this first investigation of epilepsy and air travel it appears that flying promotes an increase in seizures. About one quarter of participants reported a post flight seizure increase, a median increase of three seizures during the post flight week. There were over twice as many seizures after flying than before air travel. No participant reported having a seizure during the flight for this study. This is not surprising as the probability of a participant having an onboard seizure, based on prevalence rates,
      • Cummins R.O.
      • Schubach J.A.
      Frequency and types of medical emergencies among commercial air travelers.
      is about 1%.
      Participants who had a post flight seizure increase during this study report that this happens consistently, that air travel is associated with a fear of flight-related seizures, and, to a lesser extent, an avoidance of air travel. The position taken by the Aerospace Medical Association
      • Alvarez D.X.
      • Bagshaw M.
      • Cambell M.
      • Davis J.R.
      • et al.
      Medical guidelines for airline travel.
      and the Epilepsy Foundation of America

      Epilepsy Foundation. Aerospace Medical Association updates air travel guidelines for people with epilepsy, 2003. Retrieved 15 September 2005 from http://www.epilepsyfoundation.org/epilepsyusa/airtravel.cfm.

      that most people with epilepsy can fly safely appears not to consider the extent of seizure increase after air travel. The most significant effect of air travel on seizures appears to occur during the first few days after the flight. This is more consistent with the hypotheses that sleep disruption and sleep loss rather than hypoxia may be a causal agent in seizure increase. Seizures would be expected to occur more immediately to episodes of hypoxia.
      This study indicates that the higher the seizure rate prior to flying, the greater the likelihood of an increase in seizures after air travel. Having seizures the week prior to flight may also be a risk factor for such an increase. In contrast, those with complete seizure control appear unlikely to experience a post flight seizure, even after flying great distances.
      There is greater biological rhythm disruption and greater physiological challenge with eastward flights compared to westward flights and flights of greater distance.
      • Graeber R.C.
      Alterations in performance following rapid transmeridian flight.

      Klein KE, Wegmann HM. Significance of circadian rhythms in aerospace operations. NATO AGARD no. 247; 1980.

      It was therefore hypothesized that there would be more sleep disruption and subsequently more seizures associated with eastward and extended flights. However, contrary to expectations, there were no significant differences found regarding post flight seizure increase and the direction and distance of flight.
      Should these findings be supported by future studies, it may be concluded that those at greatest risk for post-flight seizure increases are (a) individuals with epilepsy who have had prior flight-related seizure increases and (b) individuals who have a relatively high baseline rate of seizures (in this study around four seizures per month). People with complete control over their seizures prior to flying are likely to be able to fly without an exacerbation of seizures.
      Caution should be taken in assuming that the current findings generalize to other populations of those with epilepsy. This study has the inherent limitations that result from relying on self-reported data. It is also not known to what extent the current sample reflects the population of those with epilepsy who travel by air. This sample, compared to epilepsy populations surveyed by large epidemiological studies, such as Hauser,
      • Hauser W.A.
      • Hesdoffer D.C.
      Epilepsy: frequency, causes and consequences.
      had a higher percentage of women (70%), is more predominantly Caucasian (89%), and more educated (81% having a college degree). The average distance traveled was also longer than the average flight in the U.S.

      U.S. Department of Transportation, Bureau of Transportation Statistics. 1995 American Travel Survey, BTS/ATS95-US, October 1997.

      In future investigations of epilepsy and air travel, a direct assessment of possible causal variables, such as sleep loss and hypoxia may be fruitful. Other variables may play a role in flight-related seizures, including, but not limited to, administration and effectiveness of anticonvulsants for passengers passing through several time zones, flight altitude, and psychological variables, such as state and trait anxiety. Seizures also vary in intensity and duration; it is not known if air travel influences changes in either of these seizure dimensions.
      Future studies may consider the clinical implications of a link between air travel and seizures. For example, what means are most effective for increasing seizure threshold during flight and for the post flight period? Such interventions may include increases in anticonvulsant medication, strategies to decrease jet lag, and the use of supplemental oxygen during flight. Implications for air carrier policy may also be explored so that passengers with epilepsy receive appropriate accommodations and flight crew have sufficient training and on board resources to manage seizures.

      Conclusion

      This is the first study to prospectively investigate the effect of air travel on epilepsy. Participants monitored their seizures before and after flying. Seizures were significantly more frequent after air travel, specifically for those with a past history of such increases and a relatively high baseline seizure frequency (greater than three seizures per month). It is speculated that post flight seizures may be promoted by sleep loss due to circadian rhythm disruption and possibly oxygen desaturation. Future studies may be directed at the role of sleep and oxygen desaturation on post flight seizures and possible interventions for reducing such seizures, such as increasing anticonvulsant levels, decreasing jet-lag, and using in-flight oxygen.

      Acknowledgements

      The Epilepsy Foundation of America and the Pacific Health Research Institute provided financial support for this study. The author is grateful for the support of numerous affiliates of the Epilepsy Foundation of America for their assistance with recruitment. Drs. Lois Yamauchi, Barbara DeBaryshe, Ernestine Enomoto, and Cecile Ornelles provided valued reviews of the manuscript.

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