Abstract
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.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
