The experience of nausea during sustained hyper-gravity flight with negligible angular velocity

Area of Science:

• Spaceflight physiology
• Vestibular system function
• Human factors in aviation

Background:

• Hyper-gravity flight (hyper-G) presents unique challenges to the human vestibular system.
• During head movements in hyper-G, otoliths experience increased displacement and velocity compared to 1 G conditions.
• Semi-circular canals function normally, but otoliths are affected by G-excess.

Purpose of the Study:

• To investigate the incidence and severity of nausea and vomiting during hyper-G flight.
• To compare nausea and vomiting responses in hyper-G to historical data from 1 G environments.
• To determine the role of head movements in space motion sickness during hyper-G.

Main Methods:

• 27 subjects underwent 1.8 G exposure during slow-turn flights on NASA KC-135 aircraft.
• Three experimental conditions: rest with incidental head movements, active head movements (roll/pitch), and passive head movements.
• Nausea data collected via questionnaire; electrogastrograms recorded for a subset of subjects.

Main Results:

• 26% of subjects vomited during hyper-G flight.
• Nausea levels increased initially and then stabilized, peaking during active head movements.
• Subjects who vomited reported greater gastrointestinal and somatic distress.

Conclusions:

• Observed nausea and vomiting are attributed to the G-excess effect on otoliths, not Coriolis cross-coupling.
• Nausea profiles in hyper-G vomit responders resemble those from optokinetic drum stimuli in 1 G.
• Otolith system overstimulation is a key factor in hyper-G-induced nausea and vomiting.