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Fig 1. Cranio-caudal movement of the medulla (A and B), C2 (C and D), and C6 (E and F) segments of the spinal cord in 4 healthy subjects. Velocity- and acceleration-time curves for all levels show a period of relative quiescence between 200 and 550 msec after peripheral trigger. Normalized velocity-time curves (G) and acceleration-time curves (H) at the C2 level (reflecting those of the other levels; data not shown) indicate that quiescence consistently lasted 40% of the cardiac cycle, with good consistency between subjects.
