Ventilation-Perfusion RatioOxygenPulmonary EmbolismKrypton RadioisotopesPulmonary Gas ExchangeLaser-Doppler FlowmetryHindlimbTechnetium Tc 99m Aggregated AlbuminPerfusion ImagingBlood Gas AnalysisIschemiaPartial PressurePulmonary CirculationOxygen ConsumptionNoble GasesLungPerfusionCarbon DioxideAnoxiaXenon RadioisotopesRespiration, ArtificialPulmonary VentilationOximetryVentilationOxygen Inhalation TherapyPulmonary ArteryReactive Oxygen SpeciesRespiratory Function TestsMagnetic Resonance ImagingAdministration, InhalationRespirationPositive-Pressure RespirationIntermittent Positive-Pressure VentilationTidal VolumeHigh-Frequency VentilationHypercapniaRespiratory MechanicsCerebrovascular Circulation