Ventilation-Perfusion RatioOxygenPulmonary EmbolismKrypton RadioisotopesPulmonary Gas ExchangeLaser-Doppler FlowmetryHindlimbTechnetium Tc 99m Aggregated AlbuminPerfusion ImagingIschemiaPulmonary CirculationBlood Gas AnalysisNoble GasesPartial PressureLungPerfusionXenon RadioisotopesRespiration, ArtificialCarbon DioxideAnoxiaPulmonary VentilationVentilationPulmonary ArteryOxygen ConsumptionVentriculoperitoneal ShuntRespiratory Function TestsCerebrospinal Fluid ShuntsAdministration, InhalationRespirationPositive-Pressure RespirationOximetryIntermittent Positive-Pressure VentilationOxygen Inhalation TherapyTidal VolumeHigh-Frequency VentilationPortasystemic Shunt, SurgicalRespiratory Mechanics