[abstract] METHODOLOGIES AND STRATEGIES TO DEVELOP TECHNIQUES FOR "COMPUTER-ASSISTED ANALYSIS OF GAS PHASE FORMATION DURING ALTITUDE DECOMPRESSION.

Abstract

It would be of operational significance if one possessed a device that would indicate the presence of gas phase formation in the body during hypobaric decompression. Automated analysis of Doppler gas bubble signals has been attempted for two decades, but with generally unfavorable results except with surgically implanted transducers. Recently efforts have intensified with the introduction of low cost computer programs (cf., B.A. Butler, et al.,1991). Current NASA work is directed towards the development of a computer-assisted method specifically targeted to EVA and are most interested in Spencer Grade IV. We note that Spencer Doppler Grades (I-III) have increases in the FFT sonogram and spectrogram in the amplitude domain; the frequency domain is generally not increased over that created by the normal blood flow envelop. The amplitude perturbations are of very short duration, in both systole and diastole and at random temporal positions. Grade IV is characteristic in the amplitude domain but with modest increases in the FFT sonogram and spectral frequency power from 2K to 4K over all of the cardiac cycle. Heart valve motion appears to characteristic display signals: (i) demodulated Doppler signal amplitude considerably above the Doppler-shifted blood flow signal [even Grade IV], (ii) demodulated Doppler frequency shifts are considerably greater (often several kHz) than the upper edge of the blood flow envelope. Knowledge of these facts will aid in the construction of a real-time, computer-assisted discriminator to eliminate cardiac motion artifacts. There could also exist perturbations in (a.) modifications of the pattern of blood flow in accordance with Poiseuille's Law, (b.(b.) flow changes with a change in the Reynold's number, (c.) an increase in the pulsatility index, and/or diminished diastolic flow or "runoff."