Task Effects of Microgravity on Intracranial Pressure [MICROGRAVITY ICP/LEVINE] (Completed)
Last Published:  03/26/21 03:34:00 PM (Central)
Short Title: Microgravity ICP
Responsible HRP Element: Human Health Countermeasures
Collaborating Org(s):
National Space Biomedical Research Institute (NSBRI)
Funding Status: Completed - Task completed and produced a deliverable
Procurement Mechanism(s):

The primary objective of this study is to directly measure intracranial pressure, cerebral hemodynamics, and structure of the visual apparatus during changes in hydrostatic gradients (parabolic flight) that mimic microgravity exposure. To accomplish this objective the following hypotheses will be tested.

Hypothesis 1: The transition from the upright to the supine posture increases intracranial and right atrial pressures without a clinically significant change in ocular structure. The location of the intracranial hydrostatic indifference point (where rotation around that Gy axis in the Gz plane causes no change in hydrostatic pressure) determines the magnitude of the increase in ICP during changes in posture and in microgravity; if so, this characteristic could be a testable a risk factor for visual impairment in space.


Hypothesis 2: Microgravity-induced changes (via parabolic flight) in cerebral pressures and flow will be greater than those observed during bed rest.

To test these hypotheses, we will accomplish the following specific aims:

Specific Aim 1:
We will recruit adult patients whom, because of prior medical treatment, have a brain access port from which ICP can be measured with little risk to the patient. Importantly, the selected patients will have no intracranial or cardiovascular pathology, and thus ICP can be measured accurately. Simultaneous measurement of right atrial pressure and arterial pressure will be combined with echo/Doppler measures of the middle cerebral artery, carotid and jugular vessels, and ocular ultrasound for central retinal and ciliary artery blood flow, globe size, shape and optic sheath diameter during 24 hours of head down tilt bedrest. These measures will allow a comprehensive assessment of cerebrovascular hemodynamics during routine gravitational transients. The hydrostatic indifference point will be determined in each volunteer.

Additional measurements will be made with modest increases in carbon dioxide concentrations, and during strength exercise to determine the independent and additive effects of these confounding stimuli.
Finally, after the 24 hour measurements are completed, ICP will be monitored as the subject does a series of head maneuvers including lifting the head up on a pillow, and inflation of braslets to see if these simple interventions alter intracranial pressure.

Specific Aim 2: Subjects from Aim 1 will be exposed to parabolic flight (on a separate day) to achieve brief periods of microgravity. This protocol will allow comparison between real microgravity, and usual terrestrial changes in hydrostatic gradients during daily life (e.g., from supine to upright). Similar to aim 1, measurements will be obtained at rest, during exercise, and during small increases in carbon dioxide concentrations (10 parabolas each). The study of intracranial and cardiocerebral hemodynamics in microgravity has been largely unexplored. Only a careful dissection of the pathophysiology will allow the development of effective countermeasures that could ultimately lead to reducing the risk of visual impairments during space flight. Thus, this project will serve as the essential science base required to address a potential critical impediment to safe, long-duration space flight.