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氮气与示踪气体多次呼吸洗脱技术的不同生理学原理。

The differing physiology of nitrogen and tracer gas multiple-breath washout techniques.

作者信息

Sandhu Dominic, Ritchie Grant A D, Robbins Peter A

机构信息

Dept of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, Oxford, UK.

Dept of Physiology, Anatomy and Genetics, University of Oxford, Oxford, UK.

出版信息

ERJ Open Res. 2021 Apr 19;7(2). doi: 10.1183/23120541.00858-2020. eCollection 2021 Apr.

Abstract

BACKGROUND

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 (N)-washout technique are higher than those obtained using an exogenous tracer gas such as sulfur hexafluoride. This study explored whether the pure oxygen (O) used for the N washout could underlie these higher values.

METHODS

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 O 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 O for the N washout or with air for the tracer gas washout.

RESULTS

At normal ventilation/perfusion ('/') ratios, the rate of washout of N and exogenous tracer gas was almost indistinguishable. At low '/', the N washout lagged the tracer gas washout. At very low '/', N became trapped in the acinus. Under low '/' conditions, breathing pure O introduced a marked asymmetry between the inspiratory and expiratory gas flow rates that was not present when breathing air.

DISCUSSION

The use of pure O to washout N increases O uptake in low '/' 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 N.

摘要

背景

多呼吸洗脱技术越来越多地用于评估肺功能。获得的主要统计指标是肺清除指数(LCI),但使用氮气(N)洗脱技术获得的LCI值高于使用诸如六氟化硫等外源性示踪气体获得的值。本研究探讨了用于N洗脱的纯氧(O)是否可能是这些较高值的原因。

方法

构建了一个均匀、相互通气的腺泡模型。灌注保持恒定,通过在呼吸周期中改变扫气量来调节通气。供应腺泡的血液具有标准的混合静脉成分。血液与腺泡气体之间的二氧化碳和O交换达到平衡。模型以空气或空气加示踪气体作为吸入气进行初始化。用纯O进行N洗脱或用空气进行示踪气体洗脱。

结果

在正常通气/灌注('/') 比率下,N和外源性示踪气体的洗脱速率几乎无法区分。在低'/' 时,N洗脱落后于示踪气体洗脱。在非常低的'/' 时,N被困在腺泡中。在低'/' 条件下,呼吸纯O会导致吸气和呼气气流速率之间出现明显的不对称,而呼吸空气时则不存在这种情况。

讨论

使用纯O洗脱N会增加低'/' 单位中的O摄取。这会产生一股进入腺泡的背景气流,在呼气时与流出腺泡的气流相反,从而延迟N的洗脱。

https://cdn.ncbi.nlm.nih.gov/pmc/blobs/ff9f/8053910/eb8d63398062/00858-2020.01.jpg

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