This negative pressure causes the chest wall to expand and air is drawn into the lungs through the mouth and nose.

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Here on Casualty, paramedics save a patient with a punctured lung by relieving the pressure in his chest, a procedure known as needle decompression.

BBC

He jumps out of the car -- he's been shot -- keeps pressure on his chest with his left hand, holding a service weapon with his right, he runs after the suspects.

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But sure enough, the symptoms are all there: tightening in the chest, pressure on the rib cage, shortness of breath.

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When the negative pressure is released, the chest wall "collapses" and one breathes out.

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Patients with high BMIs or with chest pain or pressure at presentation were less likely to have a false-positive activation.

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However, some people with acute pericarditis describe their chest pain as dull, achy or pressure-like instead, and of varying intensity.

CNN: Pericarditis

In addition to the drainage tubes in her chest, she required needle-drainage procedures in her abdomen every week or two to relieve the severe pressure from the litres of fluid that the cancer was producing there.

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