Ventilation-Perfusion RatioPulmonary EmbolismKrypton RadioisotopesLaser-Doppler FlowmetryPulmonary Gas ExchangeLungHindlimbTechnetium Tc 99m Aggregated AlbuminPerfusion ImagingPulmonary VentilationIschemiaNoble GasesXenon RadioisotopesRespiration, ArtificialPerfusionPulmonary CirculationOxygenBlood Gas AnalysisVentilationCarbon DioxideRespirationPartial PressurePulmonary ArteryTidal VolumeAdministration, InhalationPositive-Pressure RespirationRespiratory Function TestsAnoxiaHigh-Frequency VentilationOne-Lung VentilationRespiratory Mechanics