Blood Flow VelocityVelopharyngeal InsufficiencyCerebrovascular CirculationRegional Blood FlowUltrasonography, Doppler, TranscranialCerebral ArteriesMiddle Cerebral ArteryXenon RadioisotopesBrainLaser-Doppler FlowmetryBlood PressureCarbon DioxideBlood Circulation TimeUltrasonography, DopplerPulsatile FlowVascular ResistanceXenonTomography, Emission-ComputedIntracranial PressureHemodynamicsBlood VolumeBrain IschemiaAcetazolamideHypocapniaOphthalmic ArteryCerebral InfarctionOxygen RadioisotopesUltrasonography, Doppler, ColorHyperventilationOxygenTechnetium Tc 99m ExametazimeTomography, Emission-Computed, Single-PhotonHypercapniaEchoencephalographyMicrocirculationIofetamineOximesUltrasonography, Doppler, PulsedCoronary CirculationMagnetic Resonance ImagingHomeostasisOxygen ConsumptionAntipyrineCerebrovascular DisordersPartial PressureAnterior Cerebral ArteryRheologyHyperemiaReference ValuesTime FactorsHeart RateArteriesModels, CardiovascularRetinal ArteryDogsCiliary ArteriesOrganotechnetium CompoundsVasodilationMicrospheresEchocardiography, DopplerSubarachnoid HemorrhageCerebral VeinsCerebral AngiographyUmbilical ArteriesBlood Gas AnalysisPapioIschemic Attack, TransientVasomotor SystemBlood ViscosityPia MaterVasodilator AgentsMagnetic Resonance AngiographyUltrasonographyInfarction, Middle Cerebral ArteryCarotid Artery, InternalCircle of WillisAmphetaminesArterial Occlusive DiseasesSpectroscopy, Near-InfraredPosterior Cerebral ArteryHypotensionFlow CytometryUltrasonography, PrenatalImage Processing, Computer-AssistedCarotid ArteriesReproducibility of ResultsDiastoleVasoconstrictionCerebral CortexCollateral CirculationHematocritAutoradiographyCerebral HemorrhageTilt-Table TestRestPerfusion ImagingBrain EdemaRats, Sprague-DawleyNitrous OxideCats