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Advan. Physiol. Edu. 26: 135-136, 2002;
1043-4046/02 $5.00
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ADV PHYSIOL EDUC 26:135-136, 2002
© 2002 American Physiological Society

ILLUMINATIONS

Experiment to Help Students Understand Pulmonary Compliance

Stephen E. DiCarlo,, Heidi L. Collins and David W. Rodenbaugh

Department of Physiology, Wayne State University School of Medicine, Detroit, MI 48201

Compliance is a difficult concept for students to grasp, and in partic-ular, pulmonary compliance is quite difficult because it involves an understanding of both lung and chest compliance. To help students understand pulmonary compliance characteristics, relaxation curves for the chest cage (Fig. 1A), lung (Fig. 1B), and combined lung-chest cage (Fig. 1C) are often presented to medical students. To facilitate an understanding of the relaxation curves, we demonstrate how the curves are generated by substituting a balloon for the lungs and a tennis ball for the chest cage. Students are told that when the lung is removed from the chest cage, it closely resembles a collapsed balloon. Subsequently, a collapsed balloon is connected to a pressure transducer that is coupled to a data acquisition system. The students observe that, when pressure inside the balloon equals outside pressure, or transmural pressure is zero, balloon volume is close to zero. Starting from essentially zero balloon volume, a measured volume of air is put into the balloon, and the recoil or relaxation pres-sure associated with the addition of that air volume is recorded. Additional measured volumes of air are added to the balloon, and the corresponding recoil or relaxation pressure is recorded. Compliance of the balloon is obtained by plotting balloon recoil or relaxation pressure on the x-axis and balloon volume on the y-axis. The slope of this plot is balloon compliance.



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  		FIG. 1 Relaxation curves for the chest cage (A), lung (B), and combined lung-chest cage (C).

 
Next, students are told that, in the absence of the lung, the moderately inflexible chest cage resembles a punctured tennis ball. Subsequently, a tennis ball, punctured by an 18-gauge needle, is connected to the pressure transducer. The students observe that, when transmural pressure is zero, the tennis ball has considerable air. Starting at this initial, or equilibrium volume, a compliance curve for the ball can be constructed by the sequential addition or removal of measured volumes of air and recording the corresponding recoil or relaxation pressure. With the sequential addition of air, a positive recoil pressure is recorded. Subse-quently, the ball is returned to its equilibrium volume, and measured volumes of air are removed and the corresponding negative recoil pressures are recorded. Compliance of the ball is obtained as described above for the balloon. When plotted, data obtained during these demonstrations look remarkably like the relaxation curves obtained with the lung and chest cage (Fig. 1). During this demonstration, the students actually observe the procedures and analysis involved in generating relaxation curves. This process brings the concept "alive" and provides a fur-ther appreciation of the compliance of the lung and chest wall.




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Right arrow Citing Articles via Web of Science (3)
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Right arrow Articles by DiCarlo,, S. E.
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