Final answer:
The normal difference between inspiration and expiration when assessing costovertebral joint movement by measuring chest expansion is approximately 1-2 inches.
Step-by-step explanation:
When assessing movement of the costovertebral joints by measuring chest expansion, the normal difference between inspiration and expiration is approximately 1-2 inches. During inspiration, the diaphragm contracts and moves inferiorly, creating a larger thoracic cavity, while the external intercostal muscles move the ribs upward and outward, causing the rib cage to expand. These actions increase the volume of the thoracic cavity and lead to a decrease in intra-alveolar pressure, allowing air to be drawn into the lungs. During expiration, the diaphragm relaxes, the intercostal muscles relax, and the thoracic cavity returns to its original size, allowing air to be expelled from the lungs.