Breathing
From air to tissues: the mechanics of ventilation and its volumes, dead space, exchanges in the alveoli, the transport of oxygen and carbon dioxide in blood, and the control of breathing, with the situations where it goes wrong.
- 35 cards
- 3 topics
- Free
The outline, topic by topic
Each topic is weighted the way the exam weighs it.
- Concepts
- Scenarios
- Understand
A few cards from the deck
Inspiration: what is it?
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Air drawn in as the diaphragm and external intercostals contract and enlarge the chest.
It is always active; the diaphragm is driven by the phrenic nerve (C3 to C5).
A patient's FEV1/FVC ratio is 0.55. What kind of disorder does it indicate?
- An obstructive disorder, as in asthma or COPD
- A restrictive disorder, as in pulmonary fibrosis
- A weak diaphragm, as after phrenic nerve damage
- A diffusion problem, as in anaemia
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An obstructive disorder, as in asthma or COPD
Below 0.7, air leaves too slowly: the bronchi are narrowed.
Quiet expiration: what is it?
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Air leaving through the simple elastic recoil of lung and chest, with no muscular effort.
It becomes active during exercise, with the abdominal muscles.
Why is fast, shallow breathing less effective than slow, deep breathing?
- Air breathed in fast has no time to warm up
- Surfactant has no time to renew between breaths
- Oxygen diffuses less well when air moves fast
- Each breath fills the dead space first; when small, it brings almost nothing to the alveoli
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Each breath fills the dead space first; when small, it brings almost nothing to the alveoli
With 150 mL of dead space, a 200 mL breath renews only 50 in the alveoli.
Tidal volume: what is it?
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The volume of air moved at each quiet breath, about 500 mL in an adult.
Multiplied by the rate, it gives the minute ventilation.
A very premature baby struggles to breathe as the alveoli collapse. What is it lacking?
- Haemoglobin
- Surfactant
- A diaphragm
- Bronchi
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Surfactant
Enough surfactant is only produced late in pregnancy; it can be given.