Evaluation of Pulsed Doppler Bubble Detection

Abstract : The High Altitude Protection Function of the Crew Technology Division has used a portable Doppler array to monitor venous gas emboli in human research subjects exposed to reduced high altitudes. The existing Doppler equipment was limited in that subjects were required to maintain a specific body position to achieve consistent bubble grade analysis, especially during exercise. It was surmised that engineering modifications might resolve the dilemma. The target frequency and sound wave pulses were to be modified to maintain focus on the precordium allowing for continuous tracking of bubble sounds. A prototype, pulsed-wave, Doppler bubble detection instrument with transducers was designed and developed. This system demonstrated greater depth of penetration and the ability to localize the interrogation area; however, altitude simulation tests revealed the prototype to be unsatisfactory due to the high level of noise generated internally by the CW Doppler circuitry. Recommendations were made of redesign, but development was not pursued due to funding limitations. Also Doppler echo imaging was found to provide equal if not better analysis of bubble grades with the addition of visual cues to ensure accurate placement and timely monitoring regardless of physical activity. Bubble grades, Doppler, Bubble sounds, Doppler systems, Bubbles.