Development of methods to analyse transcranial Doppler ultrasound signals recorded in microgravity.

During space flights, several clinical syndromes may be the result of changes in cerebral circulation. The purpose of the paper is to describe the development and initial evaluation of a system for recording, processing and displaying transcranial Doppler ultrasound (TCD) waveforms from the middle cerebral artery (MCA) in microgravity. Volunteers were repeatedly subjected to 15-20 s intervals of microgravity ('near zero gravity') during flights on the KC-135 military aircraft. Continuous TCD recordings from the MCA were stored on magnetic tape. The paper describes the system that was developed to digitise the Doppler ultrasound data and markers that corresponded to the various levels of microgravity, obtain the maximum and mean Doppler waveforms, identify the waveforms and quantify them. The results demonstrate the feasibility of making TCD recordings in a microgravity environment and illustrate excellent performance of the system and its ease of operation. Quantitative waveform analysis of the recordings from the first subject studied in the supine position showed statistically significant changes in MCA velocity waveforms during microgravity.

Transcranial Doppler studies of flow velocity in middle cerebral artery in weightlessness.

Physiological adaptation to weightlessness requires changes in cardiovascular system parameters to maintain homeostasis in the presence of cephalic fluid shifts. The cerebral circulation must respond immediately to these systemic changes or impairment of cerebral function will occur. Blood flow velocities of the middle cerebral artery were measured by transcranial Doppler (TCD) ultrasound in NASA's KC-135 aircraft from four healthy subjects in the supine position. Transcranial Doppler data with accompanying acceleration information were analyzed in three segments in each parabola. Cardiac cycles for each segment of all 20 parabolas were pooled for individual subjects. A Student's t test on the data revealed statistically significant differences in the mean and peak frequencies, systolic/diastolic ratios and Doppler power between positive 2 gz and microgravity (10(-2) gz) as well as between positive 2 gz and negative 2 gz. Velocity waveform profiles differed for the first one third of each segment, with a more resistive waveform developing during the last two thirds. Changes in systemic arterial resistance and/or raised intracranial pressure may contribute to these TCD waveform changes.