Past exam of the medicine course of the University of Oxford / 1867 / First examination / Physics / 5

Enunciate Boyle's law connecting the volume and tension of a gas.

Explain the process of respiration, as far as it is due to the motion of the Diaphragm.

Assuming the lungs to contain 1600 cubic centimetres of air at the termination of an expiration, and 400 cubic centimetres to be introduced by each inspiration, if, after an expiration a vertical tube be placed in the mouth, with its lower end dipping in mercury, and, the nose being stopped, the act of inspiration be performed, to what height will the mercury rise in the tube ? The height of the mercury in the barometer being 760 m.m., and the air in the tube being neglected.

Boyle's law states that a fixed amount of gas at constant temperature obeyswhere $p$ is absolute pressure, not gauge pressure. It is an ideal-gas approximation, not an assertion that every rapid compression is isothermal.

The respiratory diaphragm contracts and lowers its dome, increasing thoracic volume. Mechanical coupling through the pleural space lets the lungs expand; alveolar pressure falls below atmospheric pressure, drawing air in. Relaxation of the respiratory diaphragm and elastic recoil drive quiet expiration. These respiratory mechanics describe ventilation, distinct from chemical cellular respiration.^[ref]

For the stipulated sealed, isothermal gas, initial and final volumes are $1600$ and $2000\mathrm{c}{\mathrm{m}}^3$. Expressing absolute pressure as a mercury-column height,The mercury column is supported by the atmospheric-to-internal pressure difference:The specified volume change belongs to the historical idealized model. Real tube-air volume, temperature changes and limits on respiratory-muscle pressure generation would affect a physical apparatus.