Blood Flow VelocityRegional Blood FlowCerebrovascular CirculationUltrasonography, Doppler, TranscranialMiddle Cerebral ArteryPulsatile FlowUltrasonography, DopplerCerebral ArteriesOphthalmic ArteryLaser-Doppler FlowmetryUltrasonography, Doppler, ColorBlood PressureVascular ResistanceHemodynamicsUltrasonography, Doppler, PulsedCoronary CirculationRheologyEchocardiography, DopplerHypocapniaRetinal ArteryCiliary ArteriesMicrocirculationEchoencephalographyUmbilical ArteriesCarbon DioxideHeart RateHyperemiaHyperventilationDiastoleModels, CardiovascularArteriesUltrasonography, PrenatalFlow CytometryUltrasonographyDogsVasodilationReference ValuesAnterior Cerebral ArteryTime FactorsOxygenVasodilator AgentsSystoleBrainIntracranial PressureHomeostasisHeart Rate, FetalSplanchnic CirculationMicrospheresPulmonary CirculationAcetazolamideXenon RadioisotopesCollateral CirculationDoppler EffectGestational AgeCoronary VesselsPregnancyCeliac ArteryReproducibility of ResultsRenal CirculationOxygen ConsumptionBlood VolumeEchocardiography, Doppler, ColorPlacental CirculationMesenteric Artery, SuperiorBlood Circulation TimeProspective StudiesVasomotor SystemHypercapniaFetal Growth RetardationBlood ViscosityEchocardiographyCircle of WillisLiver CirculationVasoconstrictionHemorheologyPartial PressureRetinal VesselsCarotid Artery, InternalFetal HeartPlethysmographyPostureTilt-Table TestAdenosineCarotid ArteriesEchocardiography, Doppler, PulsedPapaverineUterusHypotension, OrthostaticPosterior Cerebral ArteryAnalysis of VarianceVentricular Function, LeftTomography, Emission-ComputedHematocritMitral ValveXenonSensitivity and SpecificityPulseFetusVeinsCardiac Output