Gravity and Mastoid Effusion.

BACKGROUND: Asymptomatic mastoid effusions have recently been observed in astronauts returning from long-term spaceflight. In hospitalized patients, mastoid effusion increases the risks for bacterial otitis and mastoiditis. We reasoned that cephalad fluid shifts during strict -6° head down tilt bed rest could reproduce space-flight associated mastoid effusion and that artificial gravity may reverse the response. METHODS: The recent Artificial Gravity Bed Rest Study-European Space Agency study (AGBRESA) tested influences of artificial gravity during 60 days head down bed rest on a short-arm human centrifuge in healthy participants. The two intervention groups received daily artificial gravity with 30 minutes continuous artificial gravity or intermittent artificial gravity. A third group served as a control group and received no artificial gravity. We assessed cranial magnetic resonance images for mastoid effusions 1 day before bed rest, at days 14 and 52 of bed rest, and 3 days after bed rest. RESULTS: None of the participants exhibited mastoid effusions before bed rest. Six participants showed mastoid effusions at bed rest day 14 (4 continuous, 2 intermittent, 0 control). Fifteen participants showed mastoid effusions at bed rest day 52 and 3 days after bed rest (7 continuous, 3 intermittent, 5 control). CONCLUSIONS: Mastoid effusions commonly occur during strict head down tilt bed rest. The model can be applied to study the mechanisms and potential countermeasures for space flight-associated mastoid effusions. Formation of mastoid effusions during head down tilt bed rest is not prevented by daily 30 minutes short-arm intermittent or continuous centrifugation.