Blood Flow VelocityRegional Blood FlowBlood CirculationPulmonary CirculationVena Cava, SuperiorCerebrovascular CirculationUltrasonography, Doppler, TranscranialVascular ResistanceHemodynamicsCardiac OutputPulmonary ArteryMiddle Cerebral ArteryBlood PressureOphthalmic ArteryCerebral ArteriesUltrasonography, DopplerPulsatile FlowUltrasonography, Doppler, ColorCoronary CirculationRetinal ArteryLaser-Doppler FlowmetryUltrasonography, Doppler, PulsedHypocapniaCiliary ArteriesEchocardiography, DopplerEchoencephalographyHeart RateRheologyMicrocirculationCarbon DioxideUmbilical ArteriesHyperventilationDogsDiastoleUltrasonography, PrenatalAnterior Cerebral ArteryArteriesHyperemiaUltrasonographyReference ValuesVasodilator AgentsModels, CardiovascularHomeostasisVasodilationSystoleOxygenTime FactorsIntracranial PressureHeart Rate, FetalCeliac ArteryCoronary VesselsRenal CirculationSplanchnic CirculationPregnancyAcetazolamideGestational AgeBrainProspective StudiesDoppler EffectVasoconstrictionRetinal VeinBlood VolumeMesenteric Artery, SuperiorEchocardiographyFetal Growth RetardationCircle of WillisEchocardiography, Doppler, ColorCarotid Artery, InternalPartial PressurePlacental CirculationRetinal VesselsCollateral CirculationReproducibility of ResultsHemorheologyTilt-Table TestFetal HeartPosterior Cerebral ArteryOxygen ConsumptionHematocritVasomotor SystemHypotension, OrthostaticIntraocular PressureHypertensionHypercapniaHypotensionCarotid ArteriesFlow CytometryBlood ViscosityAnoxiaInfant, NewbornInfant, PrematureBlood Circulation TimePostureEyeNitroglycerinNitric OxideRenal ArteryPapaverineUterusEchocardiography, Transesophageal