Fig. 5.
Wavelet semblance analysis reflecting instantaneous phase differences between arterial blood pressure and intracranial pressure (ICP) in a patient with traumatic brain injury.61 Visual inspection of the arterial blood pressure and ICP waveforms (top) suggests that they are largely in phase, which is reflected in the semblance analysis (bottom). High semblance indicates that changes in arterial blood pressure are in phase with changes in ICP (i.e., a failure of independent control of blood flow within the brain reflects pressure passive changes in ICP). Physiologically, high semblance at shorter wavelengths (sudden changes in arterial blood pressure) is less indicative of autoregulation failure. Autoregulation acts like a high-pass filter, passing higher frequency waves and dampening lower frequency.