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Cephalic blood flow velocity and tissue oxygen desaturation during exposure to +G_z acceleration profiles
Dissertation   Open access

Cephalic blood flow velocity and tissue oxygen desaturation during exposure to +G_z acceleration profiles

David Carl Johanson
Doctor of Philosophy (Ph.D.), Drexel University
1990
DOI:
https://doi.org/10.17918/00009143
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Abstract

Incapacitation of aircrew due to Loss of Consciousness following exposure to high acceleration levels (GLOC) has been frequently reported during the past decade. While a few noninvasive measurements of the physiological parameters contributing to the phenomenon have been reported, they have generally been reported singularly. Though not directly measured, a lack of cerebral oxygenation has been indicated in several studies. Of those measurements reported, estimation of peripheral light loss (PLL) and Doppler blood flow velocity are among the most common. Estimated or measured PLL can be considered both a subjective and objective form of measurement of oxygen delivery to a specific tissue; Doppler velocity is an indirect objective measurement of the flow of blood. A more direct objective measure of oxygen delivery is provided by blood oxygen saturation. This study reports changes in measurement of oxygen saturation (SaO2) measured at the bridge of the nose and changes in Doppler blood flow velocity measured at the superficial temporal artery and the associated levels of PLL in 11 subjects exposed to accelerations up to 10 G2. Acceleration onset rates varied from 0.1 to 5 G*sec-1 and offset rates varied from 1.82 to 5.91 G*sec-1. Oxygen saturation values, following G onset, ranged from 99%-61%; doppler velocities, following G offset, demonstrated 7%-267% increases over the pre-stress values. The following observations were made. (1) Rapid Onset Rate (ROR) and Gradual Onset Rate (GOR) onset runs have to be considered separately, (2) Time of lowest SaO2 reading did not appear to have any effect on the duration (time) of run, (3) GOR and ROR exposures generally produce different relative amounts of "desaturation" at Peripheral Light Loss (PLL) or fifteen seconds at peak G (G15), (4) Offset rates didn't appear to contribute significantly to the response to G, (5) Reactive hyperemic response, as measured by the doppler, returns to pre-run value prior to the oximeter returning to pre-run values, and (6) The duration of the reactive hyperemic response provides an indication of the relative amount of tissue oxygen desaturation, (r =.85). The monitoring of blood oxygen saturation may be a potentially good measure of an impending LOC episode; further study is required to confirm this observation.

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