Blood Flow VelocityRegional Blood FlowUltrasonography, Doppler, TranscranialCerebrovascular CirculationMiddle Cerebral ArteryUltrasonography, DopplerCerebral ArteriesOphthalmic ArteryPulsatile FlowUltrasonography, Doppler, ColorCoronary CirculationUltrasonography, Doppler, PulsedBlood PressureVascular ResistanceHemodynamicsLaser-Doppler FlowmetryHypocapniaCiliary ArteriesRetinal ArteryEchocardiography, DopplerEchoencephalographyRheologyUmbilical ArteriesHyperventilationCarbon DioxideMicrocirculationUltrasonography, PrenatalDiastoleUltrasonographyHeart RateReproducibility of ResultsHyperemiaAnterior Cerebral ArteryReference ValuesModels, CardiovascularArteriesTime FactorsSystoleIntracranial PressureCoronary VesselsGestational AgeHeart Rate, FetalCeliac ArteryHomeostasisProspective StudiesPregnancyVasodilationOxygenDogsAcetazolamideVasodilator AgentsBrainDoppler EffectMesenteric Artery, SuperiorEchocardiography, Doppler, ColorFetal Growth RetardationCarotid Artery, InternalPlacental CirculationCircle of WillisSensitivity and SpecificityEchocardiographyCollateral CirculationHemorheologyFetal HeartObserver VariationTilt-Table TestFlow CytometrySplanchnic CirculationHypercapniaVasomotor SystemPosterior Cerebral ArteryHypotension, OrthostaticPosturePulmonary CirculationBlood ViscosityBlood VolumePartial PressureAnalysis of VarianceBlood Circulation TimeCardiac OutputOxygen ConsumptionPredictive Value of TestsInfant, NewbornRetinal VesselsPapaverineUterusMicrospheresCarotid ArteriesEchocardiography, Doppler, PulsedEchocardiography, TransesophagealVasoconstrictionVentricular Function, LeftRenal CirculationFetusHematocritAdenosineMitral ValveInfant, PrematurePlethysmographyXenon Radioisotopes