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Cardiorespiratory Physiotherapy: Respiratory mechanics · Muscles of Breathing

How the diaphragm, intercostals, accessory and abdominal muscles drive breathing, and what happens when they weaken.

For learning, not medical advice: for your own health, ask a doctor or another qualified professional.

Cardiorespiratory Physiotherapy · 29 questions

Try 3 questions

1. Which muscle does most of the work during quiet breathing at rest?

  1. The diaphragm
  2. The sternocleidomastoid
  3. The external intercostals
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Answer: The diaphragm

The diaphragm produces most of the tidal volume at rest; the intercostals mainly stiffen and help lift the ribcage.

2. In quiet breathing at rest, what mainly drives air out of the lungs?

  1. Contraction of the internal intercostals
  2. Elastic recoil of the lungs and chest wall
  3. Contraction of the abdominal muscles
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Answer: Elastic recoil of the lungs and chest wall

Quiet expiration is passive: the inspiratory muscles relax and the stretched lungs and chest wall spring back.

3. A complete spinal cord injury at which level is most likely to leave a person unable to breathe without a ventilator?

  1. Sixth thoracic vertebra (T6)
  2. Second cervical vertebra (C2)
  3. Seventh cervical vertebra (C7)
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Answer: Second cervical vertebra (C2)

The phrenic nerve to the diaphragm arises from C3 to C5, so an injury above C3 cuts the diaphragm off from the brain.

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