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空气流动增加压力型整体体积描记箱内压力变化的空气动力学研究

徐卫华, 沈华浩

浙江省立同德医院呼吸科，杭州 310012； 浙江大学医学院附属第二医院呼吸科，杭州 310009

摘要

动物实验中，计算小动物呼吸容量如潮气量时通常遵循Boyle 定律。而小动物在压力型体积描记箱内呼吸时，箱内气体处于不停的流动状态。为了研究气体流动本身对描记箱内压力是否产生影响，本研究采用空气动力学理论推导出压力型体积描记箱内压力变化的近似公式，并设计了三个实验对理论公式进行证明。首先，往体积描记箱内注入0.1 mL、0.2 mL 和0.4 mL 空气，结果显示，描记箱内压力迅速上升至一峰值然后下降为一水平的基线压力值。3 种容量的空气注入产生的压力变化最大值(峰压)及压力保持平稳时的压力变化值(基线压)分别为：(0.828±0.004) cmH2O、(0.684±0.003)cmH2O；(1.650±0.010) cmH2O、(1.350±0.007) cmH2O；(3.280±0.014) cmH2O、(2.658±0.011) cmH2O，峰压均显著高于基线压。其次，往体积描记箱内注入相同容量、但通气频率不同的空气，结果显示，随着注入空气的频率增加，描记箱内压力变化幅度亦显著增加。最后，用小动物呼吸机和微量移液器分别往描记箱内注入相同容量、相同频率但流量- 时间函数不同的气体，结果显示，呼吸机引起的体积描记箱内峰压及基线压均显著高于微量移液器。以上结果表明，空气流动本身在压力型体积描记箱内引起压力变化；空气流动越快，压力变化幅度也越大；流动空气的流量是时间的不同函数时，压力变化也将显著不同。因此要精确地计算小动物呼吸容量变化，需要使用更多的空气动力学原理。

关键词： 体积描记法; 空气压力; 呼吸力学; 潮气量

分类号：Q95

[Aerodynamics study on pressure changes inside pressure-type whole-bodyplethysmograph produced by flowing air.] [Ariticle in Chinese]

XU Wei-Hua, SHEN Hua-Hao

Respiration Department, Tongde Hospital of Zhejiang Province, Hangzhou 430030, China； Respiration Department, the 2ndAffiliated Hospital of School of Medicine, Zhejiang University, Hangzhou 430030, China

Abstract

When using pressure-type plethysmography to test lung function of rodents, calculation of lung volume is always based onBoyle’s law. The precondition of Boyle’s law is that perfect air is static. However, air in the chamber is flowing continuously when arodent breathes inside the chamber. Therefore, Boyle’s law, a principle of air statics, may not be appropriate for measuring pressurechanges of flowing air. In this study, we deduced equations for pressure changes inside pressure-type plethysmograph and thendesigned three experiments to testify the theoretic deduction. The results of theoretic deduction indicated that increased pressure wasgenerated from two sources: one was based on Boyle’s law, and the other was based on the law of conservation of momentum. In thefirst experiment, after injecting 0.1 mL, 0.2 mL, 0.4 mL of air into the plethysmograph, the pressure inside the chamber increasedsharply to a peak value, then promptly decreased to horizontal pressure. Peak values were significantly higher than the horizontal values(P<0.001). This observation revealed that flowing air made an extra effect on air pressure in the plethysmograph. In the secondexperiment, the same volume of air was injected into the plethysmograph at different frequencies (0, 0.5, 1, 2, 3 Hz) and pressurechanges inside were measured. The results showed that, with increasing frequencies, the pressure changes in the chamber becamesignificantly higher (P<0.001). In the third experiment, small animal ventilator and pipette were used to make two types of airflow withdifferent functions of time. The pressure changes produced by the ventilator were significantly greater than those produced by thepipette (P<0.001). Based on the data obtained, we draw the conclusion that, the flow of air plays a role in pressure changes inside theplethysmograph, and the faster the airflow is, the higher the pressure changes reach. Furthermore, the type of airflow also influencesthe pressure changes.

Key words: plethysmography; air pressure; respiratory mechanics; tidal volume

收稿日期：2009-08-19　　录用日期：2009-12-03

通讯作者：徐卫华　　E-mail: xwhzju@163.com

引用本文：

徐卫华, 沈华浩. 空气流动增加压力型整体体积描记箱内压力变化的空气动力学研究[J]. 生理学报 2010; 62 (1): 42-48.

XU Wei-Hua, SHEN Hua-Hao. [Aerodynamics study on pressure changes inside pressure-type whole-bodyplethysmograph produced by flowing air.] [Ariticle in Chinese] . Acta Physiol Sin 2010; 62 (1): 42-48 (in Chinese with English abstract).