Dr Chris Guz explained that patients often reacted as the breathing tube of the ventilator was placed in their air passage.

BBC: Barry McCarney

Later, the a tube can be passed down the throat or nasal passages so that air can be mechanically forced in by a bag or a ventilator.

BBC: Minutes matter

Mr Rogers's home features a heat-recovery ventilator a device in his basement that filters incoming air and exchanges heat between incoming and outgoing air.

ECONOMIST: Green homes