Blood Flow VelocityRegional Blood FlowUltrasonography, Doppler, TranscranialCerebrovascular CirculationMiddle Cerebral ArteryUltrasonography, DopplerOphthalmic ArteryCerebral ArteriesPulsatile FlowUltrasonography, Doppler, ColorUltrasonography, Doppler, PulsedCoronary CirculationBlood PressureVascular ResistanceHemodynamicsLaser-Doppler FlowmetryHypocapniaCiliary ArteriesRetinal ArteryEchocardiography, DopplerEchoencephalographyRheologyUmbilical ArteriesHyperventilationMicrocirculationCarbon DioxideDiastoleUltrasonography, PrenatalAnterior Cerebral ArteryHyperemiaHeart RateUltrasonographyModels, CardiovascularArteriesReference ValuesIntracranial PressureSystoleHeart Rate, FetalCeliac ArteryCoronary VesselsTime FactorsReproducibility of ResultsHomeostasisGestational AgeVasodilationPregnancyAcetazolamideDogsVasodilator AgentsProspective StudiesOxygenDoppler EffectBrainMesenteric Artery, SuperiorFetal Growth RetardationEchocardiography, Doppler, ColorCarotid Artery, InternalCircle of WillisPlacental CirculationCollateral CirculationHemorheologyTilt-Table TestFetal HeartPosterior Cerebral ArteryEchocardiographyVasomotor SystemSplanchnic CirculationHypotension, OrthostaticHypercapniaFlow CytometryPulmonary CirculationBlood ViscosityPostureInfant, NewbornBlood Circulation TimeBlood VolumeSensitivity and SpecificityPartial PressurePapaverineAnalysis of VarianceRetinal VesselsCardiac OutputUterusEchocardiography, TransesophagealEchocardiography, Doppler, PulsedVasoconstrictionOxygen ConsumptionAdenosineRenal CirculationCarotid ArteriesVentricular Function, LeftMitral ValveFetusMicrospheresPredictive Value of TestsInfant, PrematureOrthostatic IntoleranceHematocritObserver VariationBlood Circulation