Negative-Pressure Breathing Mechanics
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Mammalian inhalation works by negative pressure: the diaphragm contracts and flattens, the chest cavity expands, and falling internal pressure draws air in, per the inverse pressure-volume relationship.
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Diaphragm relaxation during exhalation shrinks the chest cavity, raising pressure and pushing air back out.
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The lungs do not actively pull themselves open — they expand passively because chest-cavity pressure around them drops first.