Ventilation-Perfusion RatioPulmonary EmbolismKrypton RadioisotopesPerfusionPerfusion ImagingLaser-Doppler FlowmetryPulmonary Gas ExchangeHindlimbTechnetium Tc 99m Aggregated AlbuminVentilationAdministration, InhalationRespiration, ArtificialPulmonary VentilationIschemiaLungNoble GasesPulmonary CirculationXenon RadioisotopesBlood Gas AnalysisOxygenCarbon DioxideHigh-Frequency VentilationPartial PressureTidal VolumeIntermittent Positive-Pressure VentilationPositive-Pressure RespirationInhalation ExposurePulmonary ArteryMyocardial Perfusion ImagingRespirationRespiratory Function TestsHigh-Frequency Jet VentilationNoninvasive VentilationAnoxiaRespiratory MechanicsVentilator WeaningSmoke Inhalation InjuryVentilators, MechanicalInhalationBurns, InhalationTomography, X-Ray ComputedIntubation, IntratrachealHypercapnia