Comprehensive Osteopathic Medical Licensing Examination (COMLEX USA) Practice

Which diaphragm motion is associated with a wider lateral expansion?

1. Pump handle

2. Bucket handle

3. Caliper

4. Flare

The correct answer is: Bucket handle

The bucket handle motion of the diaphragm is characterized by a lateral expansion of the thoracic cavity. When the diaphragm contracts during inhalation, it changes shape, moving downward and flaring out to the sides. This action resembles that of a bucket handle being lifted, leading to increased width in the rib cage. This lateral expansion is particularly important for enhancing lung capacity and allowing for more air to flow into the lungs. The mechanics of respiration involve both vertical and lateral movements, but the distinct lateral expansion observed with the bucket handle motion notably contributes to the overall volume of the thoracic cavity. In contrast, the pump handle motion primarily affects the anteroposterior diameter of the thorax, resembling the action of a pump handle rising, which leads to an increase in the front-to-back dimension rather than lateral. The caliper and flare movements do not specifically correlate with significant lateral expansion; instead, they involve different motions that do not enhance lateral chest circumference to the same extent as the bucket handle.