P O 2 is slightly below optimal due to this admixture of venous blood. O 2 uptake is obtained from measurements of O 2 in collected expired gas. The A-V oxygen difference is determined from samples collected from a systemic artery and from a catheter in the pulmonary artery. Flow is pulsatile in the pulmonary capillaries because pulse pressures are transmitted through the low resistance arterial system. This marker is dissolved in saline and injected intravenously.
Xenon is a very sparingly soluble gas which comes out in the alveoli.
Regions of the lungs containing well perfused alveoli can then be detected by an array of external counters or a scintillation camera. Regional perfusion can then be detected with external counters. Measurement by angiograms. A non-toxic radiopaque material is injected IV or into the pulmonary artery. Roentgenograms made during the period the material passes through the pulmonary circulation shows areas of flow.