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[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

Received: 2009-08-19  Accepted: 2009-12-03

Corresponding author: 徐卫华  E-mail: xwhzju@163.com

Citing This Article:

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).