Flail chest. A dangerous condition resulting from severe blunt trauma to the upper torso o...

Flail chest. A dangerous condition resulting from severe blunt trauma to the upper torso occurs when a portion of the rib cage breaks free and is no longer held rigidly in place. This condition, known as flail chest, severely limits the movement of air and oxygen into the lungs. The diaphragm and chest muscles draw in air by increasing the volume of the lungs, creating a pressure in the lungs lower than that of atmospheric pressure. The resulting pressure difference, equal to approximately 400 Pa for a resting inhalation, draws air in through the trachea. In the condition of flail chest, when the muscles attempt to increase the volume, the broken ribs are pushed into the body as shown in Figure P10.87A, compromising the amount of volume increase. Instead of flowing in from the outside, air just moves from one lung to the other (Fig. P10.87B) during a respiration cycle. Consider a case of flail chest in which four ribs have been broken at both ends as shown in the figure. Estimate the maximum force on the area of injury due to inhalation. This force is the amount of traction necessary to apply to the patient’s chest to restore normal breathing.

Figure P10.87