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MCAT Biology Question — Lung Pressure

Prior to vaccinations for poliomyelitis, widespread polio infection created wards of patients at risk of death due to loss of control of respiratory muscles. In 1928, Drinker and Shaw invented the first “iron lung,” a device that sealed the patient’s body from the neck down in a chamber with controllable pressure. The pressure change in the “iron lung” aided respiration by:


A. increasing the positive pressure in the lungs, driving diffusion of O2.

B. increasing the positive pressure in the lungs, thereby increasing lung ATP utilization efficiency.

C. negative pressure within the iron lung causing the patient’s lungs to expand.

D. delivering positive abdominal pressure driving the diaphragm.


Breathing occurs when the diaphragm and intercostal muscles expand the thoracic cavity and increase the space in the pleural cavity, thus lowering its pressure relative to atmospheric pressure. This forces air down into the lungs and expands the lungs, forming the basis of ‘negative pressure’ breathing. The iron lung mimics this by decreasing the surrounding pressure in the air around the person’s chest and abdomen, generating negative pressure that causes the patient’s lungs to expand. Thus, choice C is correct.

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