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Ultrasound as a Noninvasive Method to Assess Changes of Intracranial Volume and Pressure During Simulated MicrogravityHeadaches are commonly experienced by astronauts in microgravity and by subjects undergoing head-down tilt (simulated microgravity on Earth). Exposure to microgravity probably elevates blood pressure and flow in the head which may increase intracranial volume (ICV) and pressure (ICP) and in turn cause headache. Due to the slightly compliant nature of the cranial vault and the encasement of brain and its vasculature within this vault, any increase of ICV will increase ICP and slightly distend the cranium. Previous studies document perivascular edema and increased ICP in rhesus monkeys during head-down tilt. Elevated ICP has also been reported in humans during head-down tilt. ICP measurements in healthy humans are rare because of the invasiveness of currently-available measurement techniques. Therefore, we proposed a noninvasive ultrasound technique to assess changes of ICV and JCP. The ultrasound principle is based on compliance of the cranial vault. A 450 kHz ultrasound stimulus is transmitted through the cranium by a transducer every 7.5-10 msec. The ultrasound wave enters the brain tissue, reflects off the opposite side of the cranium and is received by the same transducer. The detected wave is compared for phase quadrature (90 deg.to transmitted wave). Because the electronic circuitry of the device maintains a 90 deg. phase (phi), any alterations in the detected wave caused by an increase of ICV and ICP will be reflected as a change in the wave frequency. Phase shift is directly proportional to path length of the wave, DELTA x, which is expressed as DELTA x = phi lambda/2 pi where lambda is wavelength. Elevated ICV and ICP expand the cranial vault and increase path length of the wave (a measure of intracranial distance). Increased path length equals reduced frequency of the detected wave. Reduced frequency is then related to elevated ICP. This technique has potential uses for ICP studies of astronauts in space and head trauma patients on Earth.
Document ID
20010114145
Acquisition Source
Ames Research Center
Document Type
Conference Paper
Authors
Murthy, G.
(NASA Ames Research Center Moffett Field, CA United States)
Yost, W. T.
(NASA Langley Research Center Hampton, VA United States)
Ballard, R. E.
(NASA Ames Research Center Moffett Field, CA United States)
Watenpaugh, D. E.
(NASA Ames Research Center Moffett Field, CA United States)
Kawai, Y.
(Tottori Univ. Japan)
Hargens, A. R.
(NASA Ames Research Center Moffett Field, CA United States)
Date Acquired
August 20, 2013
Publication Date
January 1, 1994
Subject Category
Acoustics
Meeting Information
Meeting: 2nd International Congress of Pathphysiology
Location: Kyoto
Country: Japan
Start Date: November 19, 1994
End Date: November 24, 1994
Funding Number(s)
PROJECT: RTOP 199-14-12-04
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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