Ventilation-Perfusion RatioPulmonary EmbolismKrypton RadioisotopesPulmonary Gas ExchangeTechnetium Tc 99m Aggregated AlbuminPerfusion ImagingNoble GasesPerfusionPulmonary CirculationLungXenon RadioisotopesVentilationBlood Gas AnalysisRespiration, ArtificialPulmonary VentilationOxygenPartial PressurePulmonary ArteryCarbon DioxideAdministration, InhalationRespiratory Function TestsAnoxiaHigh-Frequency VentilationTomography, X-Ray ComputedTidal VolumeIntermittent Positive-Pressure VentilationPositive-Pressure RespirationMyocardial Perfusion ImagingSensitivity and SpecificityHigh-Frequency Jet VentilationNoninvasive VentilationRespirationVentilator WeaningRespiratory MechanicsVentilators, MechanicalIntubation, IntratrachealHypercapniaTomography, Emission-Computed, Single-PhotonRespiratory Distress Syndrome, AdultTime FactorsVentilator-Induced Lung InjuryWork of BreathingLung ComplianceTracheostomyChemotherapy, Cancer, Regional PerfusionHeliumOne-Lung VentilationAir PressureCoronary CirculationIntensive Care UnitsCerebrovascular CirculationLaryngeal MasksMaximal Voluntary VentilationProspective StudiesVentilators, Negative-PressureLung Volume MeasurementsRespiratory Distress Syndrome, NewbornMasksRegional Blood FlowKryptonHemodynamicsOxygen ConsumptionRadiopharmaceuticalsIntensive CareTreatment OutcomeProne PositionPressureMagnetic Resonance ImagingRespiratory Dead SpaceAirway ResistanceOrganotechnetium CompoundsContrast MediaTracheotomyTechnetium Tc 99m SestamibiReproducibility of ResultsLung InjuryDiaphragmHypoventilationRetrospective StudiesRespiratory RateInfant, NewbornEquipment DesignApneaRespiratory Physiological PhenomenaFluorocarbonsPulmonary AtelectasisOxygen Inhalation TherapyHyperventilationNitrogen RadioisotopesAirway ObstructionIntermittent Positive-Pressure BreathingLung DiseasesDogsExercise TestHeartAcute Lung InjuryImage Processing, Computer-AssistedBlood PressureCritical IllnessPulmonary Edema