Premium
Transcranial Doppler Studies of Flow Velocity in Middle Cerebral Artery in Weightlessness
Author(s) -
Bondar Roberta L.,
Stein Flo,
Vaitkus Peter J.,
Johnston K. Wayne,
Chadwick Lorraine C.,
Norris John W.
Publication year - 1990
Publication title -
the journal of clinical pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.92
H-Index - 116
eISSN - 1552-4604
pISSN - 0091-2700
DOI - 10.1002/j.1552-4604.1990.tb03475.x
Subject(s) - supine position , middle cerebral artery , transcranial doppler , cardiology , doppler effect , medicine , hemodynamics , blood pressure , anesthesia , physics , ischemia , astronomy
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.