The differing physiology of nitrogen and tracer gas multiple-breath washout techniques.
The differing physiology of nitrogen and tracer gas multiple-breath washout techniques.
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DOI：
10.1183/23120541.00858-2020
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发表时间：
2021-04
影响因子：
4.6
通讯作者：
Robbins PA
中科院分区：
文献类型：
--
作者：
Sandhu D;Ritchie GAD;Robbins PA
多次呼吸冲洗技术越来越多地用于评估肺功能。获得的主要统计数据是肺清除指数 (LCI)，但使用氮气 (N2) 冲洗技术获得的 LCI 值高于使用外源示踪气体（例如六氟化硫）获得的值。本研究探讨了用于 N2 冲洗的纯氧 (O2) 是否会导致这些更高的值。构建了同质、相互通风的腺泡模型。灌注保持恒定，并通过改变呼吸周期期间的扫气量来调节通气。供应腺泡的血液具有标准的混合静脉成分。血液和腺泡气体之间的二氧化碳和氧气交换达到平衡。使用空气或空气加示踪气体作为吸气来初始化模型。对于 N2 冲洗，使用纯 O2 进行冲洗；对于示踪气体冲洗，使用空气进行冲洗。在正常通气/灌注 (V'/Q') 比率下，N2 和外源示踪气体的冲刷率几乎无法区分。在低 V'/Q' 时，N2 冲刷滞后于示踪气体冲刷。当 V'/Q' 非常低时，N2 被困在腺泡中。在低 V'/Q' 条件下，呼吸纯 O2 会导致吸气和呼气气体流速之间出现明显的不对称，而呼吸空气时则不会出现这种情况。使用纯 O2 冲洗 N2 可增加低 V'/Q' 装置中的 O2 吸收。这会产生流入腺泡的背景气流，与呼气期间流出腺泡的气流相反，从而延迟 N2 的冲刷。氮气和外源示踪气体多次呼吸冲刷测试之间肺清除指数的差异可以通过用于冲刷氮气产生对流气体进入低通气/灌注装置的氧气来解释 https://bit.ly/3l0xq0G
Multiple-breath washout techniques are increasingly used to assess lung function. The principal statistic obtained is the lung clearance index (LCI), but values obtained for LCI using the nitrogen (N2)-washout technique are higher than those obtained using an exogenous tracer gas such as sulfur hexafluoride. This study explored whether the pure oxygen (O2) used for the N2 washout could underlie these higher values. A model of a homogenous, reciprocally ventilated acinus was constructed. Perfusion was kept constant, and ventilation adjusted by varying the swept volume during the breathing cycle. The blood supplying the acinus had a standard mixed-venous composition. Carbon dioxide and O2 exchange between the blood and acinar gas proceeded to equilibrium. The model was initialised with either air or air plus tracer gas as the inspirate. Washouts were conducted with pure O2 for the N2 washout or with air for the tracer gas washout. At normal ventilation/perfusion (V′/Q′) ratios, the rate of washout of N2 and exogenous tracer gas was almost indistinguishable. At low V′/Q′, the N2 washout lagged the tracer gas washout. At very low V′/Q′, N2 became trapped in the acinus. Under low V′/Q′ conditions, breathing pure O2 introduced a marked asymmetry between the inspiratory and expiratory gas flow rates that was not present when breathing air. The use of pure O2 to washout N2 increases O2 uptake in low V′/Q′ units. This generates a background gas flow into the acinus that opposes flow out of the acinus during expiration, and so delays the washout of N2. Differences in lung clearance index between nitrogen and exogenous tracer gas multiple-breath washout tests can be explained by the oxygen used to wash out nitrogen generating convective flows of gas into low ventilation/perfusion units https://bit.ly/3l0xq0G