Ventilation-Perfusion RatioOxygenPulmonary EmbolismKrypton RadioisotopesPulmonary Gas ExchangeLaser-Doppler FlowmetryHindlimbTechnetium Tc 99m Aggregated AlbuminPerfusion ImagingIschemiaBlood Gas AnalysisPulmonary CirculationNoble GasesPartial PressureLungPerfusionXenon RadioisotopesRespiration, ArtificialCarbon DioxideAnoxiaPulmonary VentilationVentilationPulmonary ArteryOxygen ConsumptionRespiratory Function TestsAdministration, InhalationRespirationPositive-Pressure RespirationOximetryOxygen Inhalation TherapyIntermittent Positive-Pressure VentilationTidal VolumeHigh-Frequency VentilationRespiratory Mechanics