Ventilation-Perfusion RatioOxygenPulmonary EmbolismKrypton RadioisotopesPulmonary Gas ExchangeLaser-Doppler FlowmetryHindlimbTechnetium Tc 99m Aggregated AlbuminPerfusion ImagingIschemiaPulmonary CirculationBlood Gas AnalysisNoble GasesPartial PressureLungPerfusionXenon RadioisotopesCarbon DioxideRespiration, ArtificialAnoxiaPulmonary VentilationVentilationPulmonary ArteryOxygen ConsumptionRespiratory Function TestsAdministration, InhalationRespirationPositive-Pressure RespirationOximetryTidal VolumeIntermittent Positive-Pressure VentilationOxygen Inhalation TherapyHigh-Frequency VentilationRespiratory Mechanics