Stroke is a leading cause of death and disability in the United States. The autoregulation of cerebral blood flow that adapts to changes in systemic blood pressure is impaired after stroke. We
investigate blood flow velocities (BFV) from right and left middle cerebral arteries (MCA) and beat-to-beat blood pressure (BP) simultaneously measured from the finger, in 13 stroke and 11 healthy subjects using the mean value statistics and phase synchronization
method. We find an increase in the vascular resistance and a much stronger cross-correlation with a time lag up to 20 seconds with the instantaneous phase increment of the BFV and BP signals for the subjects with stroke compared to healthy subjects.
Human motor activity is influenced by many factors both extrinsic (work, recreation, reactions to unforeseen random events) and intrinsic (circadian and ultradian rhythms). We investigate if these factors fully account for the complex features observed in recordings of human activity. First, we measure activity over two weeks from forearm motion in subjects undergoing their regular daily routine. We show that no systematic ultradian rhythms exist in human activity during wakefulness. Furthermore, we demonstrate that during wakefulness human activity possesses previously unrecognized dynamic patterns characterized by long-range fractal correlations and nonlinear Fourier phase interactions. These patterns are unaffected by changes in the average activity level occuring within individual subjects throughout the day, on different days, and between subjects. Second, we find that these patterns persist when the same subjects undergo time-isolation laboratory experiments designed to account for the phase of the circadian pacemaker, and to control the known extrinsic factors. We attribute these newly discovered patterns to an intrinsic multi-scale dynamic regulation of human activity that is independent of known extrinsic factors, as well as known intrinsic factors (the circadian and ultradian rhythms).