What medical apparatus is a large metal cylinder with a compressor that enables the internal air pressure to be changed rhythmically around 12 times per minute?

Option C

An iron lung, also known as a tank ventilator or Drinker tank, is a type of negative pressure ventilator; a mechanical respirator which encloses most of a person's body, and varies the air pressure in the enclosed space, to stimulate breathing. It assists breathing when muscle control is lost, or the work of breathing exceeds the person's ability. Need for this treatment may result from diseases including polio and botulism and certain poisons (for example, barbiturates, tubocurarine).

The use of iron lungs is largely obsolete in modern medicine, as superior breathing therapies have been developed and due to the eradication of polio in most of the world. However, in 2020, the COVID-19 pandemic revived some interest in the device as a cheap, readily-producible substitute for positive-pressure ventilators, which were feared to be outnumbered by potential victims temporarily needing artificially assisted respiration.