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Neurovascular coupling and cerebral autoregulation are two brain intrinsic vasoregulative mechanisms that rapidly adjust local cerebral blood flow. This study examined if stenotic disease affects both mechanisms in the posterior cerebral artery. Ten patients with altogether 13 stenosed (≥50%) posterior cerebral artery (PCA) sides were studied. In addition, 6 control persons without a PCA stenosis were examined. Cerebral blood flow velocity was assessed from both PCAs with transcranial Doppler sonography; blood pressure was measured noninvasively via fingerplethysmography. Neurovascular coupling was assessed by a control system approach using a standard visual stimulation paradigm. Cerebral autoregulation dynamics were measured from spontaneous oscillations of blood pressure and cerebral blood flow velocity by transfer function analysis (phase and gain). The parameters of neurovascular coupling and cerebral autoregulation did not show relevant differences between controls, nonstenosed sides, and stenosed sides. The 3 severely stenosed PCA sides showed a trend to a minor functional flow velocity change and attenuation of the neurovascular coupling mechanism in relation to sides with moderate stenosis. Phase and gain were not altered on sides with PCA stenosis. We conclude that in a group of patients with mainly moderate stenosis of the PCA neurovascular coupling and dynamic autoregulation dynamics seem to be unaltered. [ABSTRACT FROM AUTHOR]

A reconfigurable antenna based on the liquid crystal technology is presented in this paper. The antenna comprises a planar lower reflector with an incorporated feed at its center and a polarizing grid on top as an upper reflector. The lower reflector is utilized to collimate the beam and to twist the polarization. The polarizing grid selects the polarization for the transmission and reflects the orthogonally polarized waves toward the lower reflector. Combining reflector elements with a polarizing grid allows performing additional phase adjustment on the upper reflector for beam steering. Reconfigurability is maintained by the upper reflector, in which a liquid crystal mixture is used as a tunable substrate. The liquid crystal layer is tuned with a bias voltage configuration to obtain an appropriate phase adjustment for the beam steering. As a proof of concept, the beam steering capability of the antenna is demonstrated by steering the main beam to -6^\circ, 0^\circ, and 6^\circ at 78 GHz. The measured gain at 78 GHz is 25.1 dB. The proposed antenna configuration is a promising candidate for reconfigurable, high-gain, low-profile, and low-cost antennas. [ABSTRACT FROM PUBLISHER]