Ventilation-Perfusion RatioOxygenPulmonary EmbolismKrypton RadioisotopesPulmonary Gas ExchangeLaser-Doppler FlowmetryHindlimbTechnetium Tc 99m Aggregated AlbuminPerfusion ImagingIschemiaBlood Gas AnalysisPulmonary CirculationPartial PressureNoble GasesPerfusionLungCarbon DioxideXenon RadioisotopesRespiration, ArtificialAnoxiaPulmonary VentilationVentilationOxygen ConsumptionPulmonary ArteryRespiratory Function TestsAdministration, InhalationRespirationOximetryPositive-Pressure RespirationIntermittent Positive-Pressure VentilationOxygen Inhalation TherapyTidal VolumeHigh-Frequency VentilationRespiratory Mechanics