Abstract
Headache is a common, but rarely voiced, complaint during space flights, usually attributed to space motion sickness (SMS). We used a specifically designed questionnaire based on the criteria of the International Classification of Headache Disorders, 2nd edn (ICHD-II). Of the 16 male and one female astronauts who participated in the survey, 12 (71%) reported having experienced at least one headache episode while in space, whereas they had not suffered from headache when on earth. There were in total 21 space headache episodes, of moderate to severe intensity in 71%. In two astronauts (12%) the headache and associated symptoms would match the ICHD-II criteria for migraine and in three (18%) astronauts for tension-type headache; in 12 (70%) astronauts the headache was non-specific. The vast majority of headache episodes (76%) were not associated with symptoms of SMS. We conclude that space flights may trigger headaches without other SMS symptoms in otherwise ‘super-healthy’ male subjects. We propose to classify space headache as a separate entity among the secondary headaches attributed to disorders of homeostasis.
Keywords
Introduction
Headache is a common complaint, primarily occurring in women (1). There are many putative trigger factors for migraine and other episodic headaches, including nitric oxide, alcohol, hormonal fluctuations, (relaxation after) stress, exercise, fatigue, sudden drop in barometric pressure, and acute changes in sleep or food-intake pattern (2). Travel in space is a less well-known trigger, although there are anecdotal reports of disabling headache during space flights. These headaches are usually considered to be part of the space motion sickness syndrome (SMS) (3–5). Detailed clinical descriptions of headache during space flights, and its relation to SMS, are lacking. Establishing space flight as a specific trigger for headache in otherwise ‘super-healthy’ non-headache subjects would help a better understanding of the mechanisms leading to headache. By contacting the astronauts, who replied on a voluntary basis, we sought to assess the prevalence and clinical characteristics of headache and associated symptoms during the various phases of space missions. A specifically designed questionnaire was used that was based on the criteria of the International Classification of Headache Disorders, 2nd edn (ICHD-II) (6). The majority of astronauts who participated reported having experienced disabling headaches while in space, but not on earth.
Subjects and methods
Between October 2006 and April 2008, a random selection of 17 astronauts (16 male, one female; mean age 41 years; range 28–58 years) completed a specifically designed headache questionnaire that was based on the ICHD-II (6). If headache was reported, its characteristics and accompanying symptoms were questioned in a yes/no fashion. Four specific time frames of the space flight were defined: launch (period between the launch of space vehicle and docking to the space station), stay at the space station, activity outside the space station [extravehicular activity (EVA)] and landing (between undocking from the space station and landing). The presence or absence of headache ‘on earth’ was also assessed. The descriptive clinical approach was used for data analysis. Informed consent was deemed unnecessary as none of the questions addressed sensitive topics. All subjects participated on a voluntary basis.
Results
All astronauts had passed special and very detailed medical examinations before space flight and are considered as healthy subjects. Nine astronauts had participated in short-duration space missions (up to 2 weeks; mean 10.9 days; range 8–14 days) and eight in long-duration missions (mean 201.7 days; range 150–366 days). Twelve of the 17 astronauts (71%) reported one or more episodes of headache during the space mission. There was no difference in occurrence of headache between astronauts on short- and long-duration missions. The 12 astronauts with headache reported a total of 21 headache episodes: nine during launch, nine during the stay at the space station, one during EVA and two during the landing (Table 1). Five astronauts had headache during one of the time frames, six during two time frames and one during all four time frames. The latter was the only one who experienced headache during EVA. Headache severity ranged from mild to severe, with mild intensity in 29% and moderate to severe intensity in 71%, but was usually reported as moderate (65%). This is how one of the astronauts described the headache: ‘So here I was with a Big Headache. I pressed my head against one of the cargo bags to help with my Headache. I rolled up in my sleeping bag with my head pushed against the cargo and spent most of the day sleeping’. Sixty-four per cent of the astronauts took analgesics for their headache. Two of the individual headache episodes (both during launch) matched the ICHD-II criteria for a migraine attack. The remaining headache episodes were tension-type or non-specific (Fig. 1). In 77% of the episodes, headache was described as ‘exploding’ and/or ‘a heavy feeling’: by eight out of nine astronauts during the launch, by seven out of nine during the stay at the space station, by one astronaut during the EVA and by two out of two during the landing. When each independent headache episode was assessed, 16 (76%) demonstrated no association with the main symptoms of SMS, such as nausea, vomiting or vertigo. None of the astronauts had a history of recurrent headache on earth.
Characteristics of headache episodes during space mission (n = 21)
Headache classification during space mission.
Discussion
Although headache in space is generally considered not to be a major issue, our study has demonstrated that disabling headache frequently occurs during space missions in subjects who otherwise do not suffer from headache while on earth. This is in accordance with previous studies (7–9). As astronauts are known to be reluctant to reveal all physical complaints (10), the true headache incidence could be even higher than reported here.
The majority of the astronauts experienced headache episodes of moderate intensity, which in many cases required the use of analgesics. Although headache during space flights is usually attributed to SMS (5, 9–12), most astronauts who reported headache did not experience associated SMS symptoms. The generally held view that headache is just a symptom of SMS could thus not be confirmed.
Most headache episodes did not fulfil the ICHD-II criteria for one of the primary headache types. Two headache episodes fulfilled the criteria for a migraine attack that include nausea, vomiting and photo- and phonophobia. As these symptoms may sometimes also be part of the motion sickness syndrome, it is difficult to establish the true nature of these symptoms by using only a questionnaire. Occurrence of the headache only under specific conditions of microgravity would classify it as a secondary headache. To describe headache, most astronauts used terms such as ‘exploding’ and/or ‘a heavy feeling’, confirming previous observations and suggesting a change in intracranial pressure (13, 14). This is compatible with headache attributed to disorders of homeostasis [G44.882] (6), which can change during a state of microgravity (5, 15). Certain haemodynamic changes might explain the occurrence of space headache. Alteration of cerebral blood flow and volume have been shown during exposure to microgravity (12, 16). The most striking change is the cephalad fluid shift, when body fluid redistributes and the blood volume in the upper body increases (17, 18). The fluid shift towards the brain and probable brain oedema could lead to an increase in intracranial pressure (9, 16, 19). Insofar as microgravity is also known to induce hypoxia, it also might be considered as a plausible trigger for space headache (20).
We conclude that space headache is a common and often isolated, disabling complaint during space flight. It should be classified as a separate entity among the secondary headaches attributed to disorders of homeostasis.