Advan. Physiol. Edu. 27: 86-87, 2003;
doi:10.1152/advan.00061.2002
1043-4046/03 $5.00
ADV PHYSIOL EDUC 27:86-87, 2003
© 2003 American Physiological Society
ILLUMINATIONS
Pulmonary ventilation teaching aid: part 2
Brad Stockert
Program in Physical Therapy, California State University, Sacramento, Sacramento, CA 95819. bstockert{at}csus.edu
Since writing the article titled "Pulmonary ventilation teaching aid" (Stockert B, Adv Physiol Educ 27: 41–42, 2003), we have continued to use the salad tongs and rubber band model to teach ventilation mechanics and several clinical correlates. The original article dealt primarily with normal ventilation mechanics and changes in the lungs, i.e., the rubber bands, that occur with common pulmonary disorders, e.g., pulmonary fibrosis and chronic obstructive pulmonary disease. We have developed several additional clinical correlates related to changes in the chest wall, i.e., the salad tongs. Those clinical examples are presented here. The materials needed for this demonstration are several rubber bands and a pair of metal salad tongs with a hinge (Fig. 1).
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FIG. 1 Salad tongs with a metal hinge, several rubber bands, and a small weight are required for this demonstration.
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If a rubber band is placed around the two arms of the salad tongs, the triangular area between the two arms of the tongs and the rubber band can be used to represent the volume of air in the lungs at a given point in time (Fig. 2). A slight, inwardly directed bend in one of the arms of the salad tongs can be used to simulate some orthopedic conditions that result in restrictive lung disorders. The inwardly directed bend decreases the area within the triangle formed by the arms of the salad tongs and the rubber band (Fig. 3). The decrease in area provides visual confirmation of the decrease in inspiratory reserve and vital capacity seen in people with severe thoracic kyphosis, scoliosis, and Dowager’s hump.
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FIG. 2 A rubber band around the arms of the salad tongs forms a triangle. The shaded area within the triangle represents the volume of air contained within the lungs at a given point in time.
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FIG. 3 An inwardly directed bend in one arm of the salad tongs decreases the area within the triangle, i.e., the volume of air contained within the lungs at a given point in time.
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We have asked students to visualize what the effect would be if the hinge of the salad tongs was rusty and hard to move. Most students have little difficulty picturing that the movement of the arms of the tongs would require more muscular effort and the movement would be limited in the available range of motion. This situation provides a mental picture of some of the mechanisms involved in restrictive lung disorders resulting from ankylosing spondylitis and osteoarthritis of the spine. Each of these disorders limits inspiratory movement of the chest wall, makes the movement more difficult to perform, and requires more muscular effort to complete. As a result, people with these disorders generally have an increased work of breathing and decreased inspiratory reserve volume and vital capacity.
Students often have difficulty perceiving that obesity produces ventilation problems. To demonstrate the effect of obesity on ventilation, place the long axis of the apparatus in the horizontal plane with one arm down on a surface and one arm pointing up (Fig. 4). Place a small weight on the top arm of the tongs. This combination demonstrates that more muscular effort is required to separate the arms of the tongs, i.e., more muscular effort is required to inhale, resulting in an increase in the work of breathing and/or a decrease in inspiratory reserve volume and vital capacity.
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FIG. 4 A weight placed on the top arm of the salad tongs provides a demonstration of the effect of obesity on the increased effort required for inhalation.
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This article has been cited by other articles:
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P. McCulloch
A SIMPLE MODEL ILLUSTRATING THE BALANCING FORCES OF LUNG AND CHEST WALL RECOIL
Advan Physiol Educ,
September 1, 2004;
28(3):
125 - 127.
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Copyright © 2003 by the American Physiological Society.
