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Objective To investigate the relationship between end-tidal CO2 (EtCO2) and seasickness (motion sickness at sea) during an Antarctic voyage. Methods In this study, we measured EtCO2 and severity of seasickness using the subjective symptoms of motion sickness (SSMS). We sampled EtCO2 and SSMS every 3–4 h for 3 days from the date of sail in 16 healthy subjects. This experiment was performed on an icebreaker (standard displacement: 12,650 t). Results Since 2 subjects dropped out because of severe motion sickness, available data were collected from 14 subjects. On analysis of all data of all subjects grouped together, there seemed to be a significant negative correlation between EtCO2 and SSMS (R = −0.27, P = 0.0005). However, in individual subjects, this correlation was not obvious. During the voyage, EtCO2 level in the seasickness susceptible group was lower than that in the non-susceptible group (P = 0.018). Both EtCO2 increasing in the non-susceptible group and decreasing in the susceptible group contribute to the difference in EtCO2 levels. We suggest that the cause of this increase in EtCO2 level in the non-susceptible group was unwitting slow and deep breathing to resist seasickness. Conclusion We revealed that for seasickness during an Antarctic voyage, EtCO2 level relates to susceptibility, but not occurrence or severity. Measurement of EtCO2 levels may be useful to identify seasickness-susceptible persons and to efficiently prevent seasickness.

We report two cases of spontaneous intracranial hypotension (SIH) that presented with orthostatic hearing impairment. Pure tone audiometry in case 1 and distortion-produced otoacoustic emissions (DPOAEs) in case 2 clearly revealed orthostatic low-frequency hearing impairment. The symptoms resolved with conservative therapy in case 1, but they did not resolve completely after three treatments with epidural blood patch in case 2. The orthostatic changes at low-frequency that were present in both examinations indicated a relative endolymphatic hydrops due to SIH. Both otological examinations were useful to infer the pathophysiology of hearing impairment associated with SIH.