[Labyrinth]
Evaluation of vestibular dysfunction induced by a long term stay in the ISS

RESEARCH OVERVIEW

• The vestibular organ is situated in the inner ear bony labyrinth, and comprises two components: 1) the otolith organs which perceive linear accelerations (gravity); and 2) the semicircular canals which perceive roll accelerations (rotational movements). The vestibular system sends neural signals to the central nervous system and regulates variety of biological functions such as body balance, eye movements, blood pressure, and muscle-bone metabolism. However, the vestibular system is known to be highly plastic, (i.e., if subjects are exposed different gravitational environment [micro-gravity in space]), the function of the system is altered. The Evaluation of Vestibular Dysfunction Induced by a Long-term Stay in the ISS (Labyrinth) investigation tests this hypothesis by separately examining the otolith and the semicircular function of an ISS crew member, before and after flight. Furthermore, this investigation also tests the hypothesis that a weak galvanic vestibular stimulation (GVS) might mitigate the impaired vestibular function.
• These studies are important, because the impaired vestibular system may relate spaceflight-induced medical problems, i.e., gravity sickness, impaired body balance, orthostatic hypotension, muscle and bone atrophy. To examine mechanisms of spaceflight-induced medical problems, otolith and canal functions are separately evaluated and tested as to whether weak GVS can relieve impaired vestibular function.

SPACE APPLICATIONS

An impaired vestibular system may relate to spaceflight problems such as motion sickness and impaired balance. This investigation supports crew member health during flight and benefits crew members with balance disorders and orthostatic hypotension upon return to Earth’s gravity.

EARTH APPLICATIONS

This investigation supports development of countermeasures for the elderly and others on Earth who experience orthostatic intolerance, or problems with blood flow, blood pressure, and heart rate when moving to an upright position after sitting or lying down.

OPERATIONAL REQUIREMENTS AND PROTOCOLS

Preflight and postflight baseline data collection is conducted 4 times: 1) L–3 (–0/+2) months; 2) R+0 (–0/+2) days; 3) R+2 weeks (+/–4 days); 4) R+2 (+/–0.5) months. All procedures are noninvasive and finished in 1 hour.

To evaluate otolith function, ocular vestibular evoked myogenic potential (oVEMP) and cervical VEMP (cVEMP) are measured in these tests. Myogenic potentials are measured from the eyelid muscle, and the cervical muscle is excited by sound or vibration.

To evaluate canal function, an air caloric test is performed. In this test, eye movements are video recorded, while air of 48ºC and 24ºC is injected from the external auditory canal.

To evaluate balance ability, a balance test is performed. The subject stands on a balance board for 60 seconds, with or without the eyes open, and with or without weak GVS.