Ventilation-Perfusion RatioOxygenPulmonary EmbolismKrypton RadioisotopesPulmonary Gas ExchangeLaser-Doppler FlowmetryHindlimbTechnetium Tc 99m Aggregated AlbuminPerfusion ImagingIschemiaPulmonary CirculationBlood Gas AnalysisNoble GasesPartial PressureLungPerfusionRespiration, ArtificialXenon RadioisotopesCarbon DioxideAnoxiaPulmonary VentilationVentilationPulmonary ArteryOxygen ConsumptionRespiratory Function TestsAdministration, InhalationStress, MechanicalPositive-Pressure RespirationRespirationTidal VolumeOximetryIntermittent Positive-Pressure VentilationOxygen Inhalation TherapyHigh-Frequency VentilationRespiratory MechanicsVentilators, Mechanical