Blood Flow VelocityRegional Blood FlowUltrasonography, Doppler, TranscranialCerebrovascular CirculationMiddle Cerebral ArteryCerebral ArteriesUltrasonography, DopplerOphthalmic ArteryPulsatile FlowUltrasonography, Doppler, ColorCoronary CirculationUltrasonography, Doppler, PulsedBlood PressureVascular ResistanceHemodynamicsLaser-Doppler FlowmetryHypocapniaRetinal ArteryCiliary ArteriesBlood VesselsEchocardiography, DopplerEchoencephalographyRheologyUmbilical ArteriesMicrocirculationCoronary VesselsHyperventilationCarbon DioxideDiastoleUltrasonography, PrenatalArteriesAnterior Cerebral ArteryRetinal VesselsHyperemiaHeart RateUltrasonographyModels, CardiovascularReference ValuesVasodilationIntracranial PressureCeliac ArterySystoleHeart Rate, FetalVasodilator AgentsHomeostasisTime FactorsGestational AgeDogsAcetazolamidePregnancyCollateral CirculationOxygenDoppler EffectBrainMesenteric Artery, SuperiorCircle of WillisCarotid Artery, InternalProspective StudiesPlacental CirculationReproducibility of ResultsFetal Growth RetardationHemorheologyVasomotor SystemEchocardiography, Doppler, ColorSplanchnic CirculationFetal HeartPosterior Cerebral ArteryTilt-Table TestPulmonary CirculationEchocardiographyHypercapniaVasoconstrictionHypotension, OrthostaticFlow CytometryBlood ViscosityLymphatic VesselsCarotid ArteriesBlood VolumeBlood Circulation TimePosturePartial PressurePapaverineVeinsUterusCoronary AngiographyAdenosineRenal CirculationEchocardiography, TransesophagealCardiac OutputEchocardiography, Doppler, PulsedBlood CirculationOxygen ConsumptionMicrospheresFetusInfant, NewbornSensitivity and SpecificityVentricular Function, LeftAnalysis of VarianceMagnetic Resonance AngiographyArterial Occlusive Diseases