static mechanics of breathing Flashcards

1
Q

what are the physical forces that influence breathing mechanics

A

static - influence gas flow, independent of volume change - elasticity, compliance, surface tension

dynamic - affecting flow of air into and out of lung as volume changes with time - flow, resistance, turbulence

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2
Q

describe what happens when you breath

A

when u breathe in rib cage expands outwards and upwards, lungs expand with expansion, air pressure falls below air pression in room creating vacuum causing air to move from mouth to lungs

breathe out - relax muscles in rib cage and let elastic recoil of lungs take over, recoil inwards of own elastic recoil creating air pressure that is slightly higher than air pressure in room, air moves out

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3
Q

what is meant by lung compliance

A

Lung with high compliance is easily distended

Lung with low compliance is difficult to distend

compliance varies inversely with lung elasticity

Static compliance is measured under conditions of NO GAS FLOW

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4
Q

what can affect compliance

A

diseases like pulmonary fibrosis decrease it

disease like emphysema increase it due to poor elastic structure

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5
Q

how do elastic forces link pleural pressure to alveolar pressure

A

elastic recoil - elastin in alveoli acts as an inward collapsing force

opposing elastic recoil of ribs acts as an outwards expanding force

balance of forces results in a sub-atmospheric intrapleural pressure

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6
Q

what is intrapleural pressure during quiet breathing

A

sub-atmospheric

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7
Q

what allows alveolar pressure to go above atmospheric during quiet breathing

A

elastic retraction

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8
Q

what is Pulmonary compliance / elastic recoil
produced by

A

elastic connective fibres - elastic mesh around alveoli

alveolar surface tension

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9
Q

how do you calculate compliance

A

change in volume/change in pressure

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10
Q

describe surface tension in the alveolus

A

resists alveolar stretch, so high surface tension decreases compliance reducing alveolar size and more energy required to inflate lungs

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11
Q
A
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12
Q
A
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13
Q
A
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14
Q

what does small variation in alveolar size/volume cause

A

as small diameter bubbles have higher surface tension that larger ones, variation causes small alveoli to collapse into larger ones -NOT GOOD

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15
Q

how do you calculate the pressure in bubble

A

(2 x surface tension) / radius of bubble

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16
Q

how does pulmonary surfactant stabilise alveolar structure

A

by reducing surface tension

17
Q

what is pulmonary surfactant composed of, what is it secreted by

A

Dipalmitoyl phosphatidyl choline (DPPC)
packaged around surfactant proteins (A-D)

secreted by type II alveolar epithelial cells

18
Q

what is the role of pulmonary surfactant

A

reduces surface tension in alveoli

  • preventing collapse of alveoli during lung expansion and contraction
  • reduces pressure required to inflate lungs
19
Q

what is the effect of surfactant on stability of alveoli

A

as radius falls, surfactant molecules crowded together and surface tension is reduced therefor smaller alveolus stabilised

20
Q

Alveoli also stabilised by mechanical interactions
between neighbouring alveoli. Prevent alveolar
collapse.

A
21
Q
A