Skip Navigation


Author(s): David R. Caprette, PhD
Showing Results for: force Return to Presentation

The Science of Vital Lung Capacity

Students observed the following properties of air while conducting this activity.

  • Air takes up space and the lungs hold air.
  • Air travels in and out of the lungs. Breathing is controlled by changes in the size of the chest cavity. The work of breathing is accomplished by the diaphragm (a thin layer of muscle at the base of the chest cavity) and muscles in the walls of the chest. The diaphragm is responsible for about 75% of the air flow in breathing. At rest, it is relaxed and bulges upward. When we are about to take a breath, the diaphragm muscles tighten, move downward, and increase the space available (and decrease total pressure) within the chest. Outside air rushes in to fill this space. As we exhale, the muscles of the chest and diaphragm relax, the space in the chest cavity contracts, and air is forced out of the lungs. 
  • People differ in the amount of air that they can blow out of their lungs. The lungometer students built for this activity models the machine (called a spirometer, see slide) that doctors use to measure vital lung capacity in their patients. The spirometer is used frequently to assess patients’ asthma, emphysema and other respiratory conditions. People with lung diseases often have limited vital lung capacities. Asthma, for example, is caused by inflammation of the lungs and constriction of the airway, which can lead to difficulty in breathing and a reduced vital lung capacity.