Medical Hypotheses Is there a connection between long airplane flight, venous thromboembolism, and sleep-disordered breathing? Maria-Cecilia Lopes a, * , Henrique Salmazo da Silva b , Lia Rita A. Bittencourt a , Ronald D. Chervin c , Sergio Tufik a a Department of Psychobiology in UNIFESP, R. Dr. Napolea ˜o de Barros, 925, CEP: 04024-002, Sa ˜o Paulo, SP, Brazil b Department of Gerontology in Sao Paulo University (USP), Sao Paulo, Brazil c Michael S. Aldrich Sleep Disorders Laboratory, Ann Arbor, MI, USA Received 19 December 2007; received in revised form 13 February 2008; accepted 16 March 2008 Available online 23 July 2008 Abstract Commercial passenger flights have been increasing around the world. The effect of these flights on health is unclear. Venous thromboembolism has been noted after recent long-distance airplane flight, even in the absence of other risk factors. Hypoxia caused by the low ambient pressure during flights could contribute, and individuals with obstructive sleep apnea may be particularly vul- nerable. The association between the effects of long airplane travel and sleep-disordered breathing deserves further study. Ó 2008 Elsevier B.V. All rights reserved. Keywords: Long-travel; Venous thromboembolism; Long airplane flight; Sleep-disordered breathing 1. Introduction Commercial passenger flights have been increasing around the world in recent decades; approximately two billion people now travel each year [1,2]. The effect of these flights on health is unclear. An association between prolonged sitting and venous thromboembo- lism (VTE) was first recognized during the Second World War, with reports of fatal pulmonary embolism (PE) in people who slept at desk chairs. The frequency of VTE and PE overall is controversial; reported preva- lence ranges from 1% to 10%, and retrospective clinical series suggest that up to 20% of patients presenting with thromboembolism have undertaken recent air travel [3]. Long-distance air travel has been associated with a high risk of pulmonary embolism which can be fatal [4]. Nev- ertheless, the pre-existing risk factors for VTE are still unclear. Preliminary data suggest that obstructive sleep apnea syndrome (OSAS) may increase risk for VTE independently of the severity of the disease [5,6]. How- ever, the preliminary data published in the two letters to the editor just referenced have not been replicated or confirmed in full-length peer-reviewed reports to our knowledge. Hypoxia induced by low ambient oxygen levels in air- plane cabins can be associated with changes in platelets [7]. Platelet number or function may be altered in circumstances (high altitude) that may also induce hemostasis [8]. It is well recognized that altered platelet aggregation is one of the strongest risks for venous thromboembolism. Hypoxia-induced platelet activation and aggregation may be due to increased circulating cat- echolamine levels but it is not known whether hypoxia can affect platelets directly [9]. Hypoxic conditions dur- ing flight also could cause changes in many other domains of health, biological function, and quality of life. The transport of oxygen to tissues for physiological functions depends on the presence of oxygen in the 1389-9457/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.sleep.2008.03.019 * Corresponding author. Tel.: +55 11 5908 7000; fax: +55 11 5539 6933. E-mail address: m.cecilialopes@psicobio.epm.br (M.-C. Lopes). www.elsevier.com/locate/sleep Sleep Medicine 10 (2009) 385–388