Lecture 5 - Breathing Function Flashcards Preview

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Flashcards in Lecture 5 - Breathing Function Deck (12):

Respiration and energy equilibrium

- inspiration is active: uses diaphragm contraction
- expiration is passive, doesnt use any energy and tries to return to mechanical equilibrium and restore pressure gradient
-forced expiration requires abdominal muscle contraction - not at equlibrium


Normal breathing

- diaphragm contracts and moves downward
- negative pressure in lung compared to mouth, air flows down
- Pulling against: elastic recoil of the chest wall and lung, resistance in airways (size + length of tube determines resistance to airflow)
- negative pressure in the alveoli on inspiration
- expiration - pressure in chest wall wants to go back to equilibrium point: relaxation (chest and lung recoil back)



- At usual breathing volume, alveoli are smaller at lung base
- lung functions unevenly, due mostly to gravity
- tidal breathing occurs mostly from the lung base
- normal inspiration is active whereas expiration is not
- basal airway tends to close in the elderly


Gravitational effects

- creates a different negative pressure in various parts of the lung
- upper lobe: 10 cm H20, lower lober 2.5cm H20
- we breathe mostly from the bottom of our lung because the alveoli are less stretched by gravity cause rest on diaphragm
- top lung more stretched: negative pressure increases


Blood vessels are within the alveolar walls - compression

- floppy blood vessels run inside alveolar walls: pressing of capillary when alveoli inflates reduces flow


Airways are outside of alveoli: dilate

- dilate when you breathe in
- so inspiration decreases circulation and increases airway space
- decrease in circulation rate favors exchange


Pleural pressure

- the airways and blood vessels are affected by pleural pressure
- therefore their calibre and hence function are affected by gravity/posture


Lung apices

- alveoli more distended - less ventilation
- blood vessels are more constricted - less perfusion

- ** compared to lung bases
- this is why we breathe more from the bottom of our lungs


Pleural pressure - effects on ventilation

Another reason why we breathe with bottom of lung

- lung bases are more compliant - we therefore breathe from the dependent parts of the lung because compliance determines ventilation in normals
- pressure gradient higher in apex : harder to work -> not much breathing
- big changes in l;ung volume where alveoli are small (base of lung)
- highly compliant lung -> very little elastic recoil -> have to fight against little pressure


Effects of ageing on lung function

- negative pressure decreases
- lung becomes more compliant as we grow older
- too low negative pressure in base - airway closure - use more the apex of lungs
- lung elastic recoil decreases
- ventilation becomes more uneven
- airway closure increases
- closing volume is earlier


- Distribution of ventiltation

- ventilation is inherently heterogeneous
- based mostly on effects of gravity on lung
- ventilation becomes more heterogeneous with age/airway disease
- change in ventilation distribition is an early abnormality of airway disease


Mechanical consequences of obstructive airway disease

- airway narrowing
- hyperinflation
- airway closure

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