Ventilation-Perfusion RatioOxygenPulmonary EmbolismKrypton RadioisotopesPulmonary Gas ExchangeLaser-Doppler FlowmetryHindlimbTechnetium Tc 99m Aggregated AlbuminPerfusion ImagingIschemiaBlood Gas AnalysisPulmonary CirculationNoble GasesPerfusionLungPartial PressurePressureXenon RadioisotopesRespiration, ArtificialCarbon DioxideAnoxiaPulmonary VentilationBlood PressureVentilationPulmonary ArteryOxygen ConsumptionRespiratory Function TestsAdministration, InhalationPositive-Pressure RespirationRespirationTidal VolumeOximetryIntermittent Positive-Pressure VentilationOxygen Inhalation TherapyHigh-Frequency VentilationRespiratory Mechanics