Valind S O, Rhodes C G, Jonson B
J Nucl Med. 1987 Jul;28(7):1144-54.
The accuracy of the steady-state measurement of ventilation by means of a short-lived insoluble inert gas tracer rests with the validity of the steady-state flow equation. This has previously been applied to the qualitative assessment of regional ventilation using krypton-81m, but may potentially be used for the calculation of regional alveolar ventilation per unit alveolar gas volume--(VA/VA)cal--from measurements of the alveolar concentration of the tracer. The steady-state alveolar tracer concentration was calculated for the course of a breathing cycle, using a lung model featuring airways dead space and tidal gas flow. The calculations were made by computer simulations of a lung, characterized by predefined values of parameters describing the lung structure and the mode of ventilation. In the normal lung of supine man at rest (specific alveolar ventilation, ranging from 1.0 to 3.5 min-1) the errors of (VA/VA)cal relative to the predefined true values range from an overestimation by some 3% in the low ventilation regions to an underestimation by 8% in the best ventilated regions. The errors mainly result from ventilation of the airways dead space, which will influence the distribution of tracer in the lung by the transfer of tracer between regions by way of the common dead space and by the decay of tracer during its transport through the bronchial tree.
通过使用短寿命不溶性惰性气体示踪剂进行通气稳态测量的准确性取决于稳态流量方程的有效性。此前，该方程已应用于使用氪 - 81m对局部通气进行定性评估，但也有可能用于根据示踪剂肺泡浓度的测量来计算单位肺泡气体体积的局部肺泡通气量——(VA/VA)cal。利用一个具有气道死腔和潮气量气流的肺模型，计算了一个呼吸周期内的稳态肺泡示踪剂浓度。计算通过对肺的计算机模拟进行，该肺的特征由描述肺结构和通气模式的参数的预定义值确定。在静息仰卧男性的正常肺中（比肺泡通气量范围为1.0至3.5 min-1），(VA/VA)cal相对于预定义真实值的误差范围从低通气区域高估约3%到最佳通气区域低估8%。误差主要源于气道死腔的通气，这将通过示踪剂在各区域间通过共同死腔的转移以及示踪剂在通过支气管树运输过程中的衰变来影响示踪剂在肺内的分布。
