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Respiratory > 13. Lung mechanics > Flashcards

13. Lung mechanics Flashcards

1
Q

Flow volume loop: Downward deflection

A

Inspiratory

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2
Q

Flow volume loop: Upward deflection

A

Expiratory

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3
Q

How to calculate L per minute

A

L per s X 60

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4
Q

Flow volume loop: Outer lines

A

Respiratory flow envelope
No matter how hard you try you can’t go beyond those bounds
Anatomical limitation

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5
Q

Flow volume loop: little loop in middle

A

Tidal volume

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6
Q

Flow volume loop: left and right on the x axis

A

Left: Higher lung volume (total lung capacity)
Right: Lower lung volume (residual volume)

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7
Q

Where is lung volume higher on Flow volume loops?

A

Where the axis cross

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8
Q

Flow volume loop: mild COPD

A 
Curve shifts left, lungs operating at higher volume (as Residual volume increases)
Flow smaller (Curve is diminished in size)
Distinct shape: coving in expiratory flow, as air is moving through smaller airways which have mucous secretions and bronchoconstriction so flow rate is lower
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9
Q

Flow volume loop: severe COPD

A

Shorter curve (peak expiratory flow decreases)
Displaced to the left
Coving is much more severe
Narrower (Vital capacity decreases)

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10
Q

Flow volume loop: Restrictive disease

A

Curve shifts right: lungs operating at lower volume (as lungs blocked, cant expand further)
Narrower (Vital capacity decreases)
Peak is slightly lower

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11
Q

Flow volume loop: variable extra thoracic obstruction

A

Normal Expiratory curve

Inspiratory curve is blunted: still getting air in but limited

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12
Q

Flow volume loop: variable intrathoracic obstruction

A

Normal inspiratory curve

Blunted expiratory curve

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13
Q

Flow volume loop: Fixed airway obstruction

A

Both inspiratory and expiratory curves are blunted

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14
Q

Describe obstructive lung disease

A

Flow of air in and out of the lung is obstructed
Reduced ability to exhale air completely
Lungs are operating at higher volumes

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15
Q

Describe restrictive lung disease

A

Inflation/ deflation of lung or chest wall is restricted

Lungs operating at lower volumes

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16
Q

Chronic causes of obstructive lung disease

A

COPD:
Empysema
Bronchitis

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17
Q

Acute causes of obstructive lung disease

A

Asthma

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18
Q

Pulmonary causes of restrictive lung disease

A

Lung fibrosis

Interstitial lung disease

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19
Q

Extrapulmonary causes of restrictive lung disease

A

Obesity

Neuromuscular disease

20
Q

Summarise values in COPD

A

Amount of air trapped in (residual volume) increases because bronchoconstriction and elasticity of parenchyma of alveolar subunits deteriorates.
Vital capacity and all other volumes decrease

21
Q

Summarise values in restrictive lung disease

A 
Everything decreases (including residual volume)
Restrictive disorders can have intrathoracic or extra-thoracic aetiologies
22
Q

Shape of transrespiratory system pressure

A

Sigmoid
Healthy= middle of curve
Takes a lot of effort to be at the extremes of the curve

23
Q

Transrespiratory system pressure curve in restrictive disease

A

Curve squashed down (vital capacity decreased)

Curve stretched sideways (more effort required to move air in and out as chest wall-lung interface is less compliant)

24
Q

Transrespiratory system pressure curve in obstructive disease

A

Curve shifts up: operating at higher volumes
Smaller vital capacity
Tissue becoming more compliant

25
Q

Compliance

A

Tendency of a structure to distort under pressure

Change in volume / change in pressure

26
Q

Elastance

A

Tendency of a structure to recoil to its original volume

Change in pressure / change in volume

27
Q

Compliance, elastance and airway resistance in obstructive lung disease

A

Compliance: Increases
Elastance: Decreases
Airway resistance: Increases

28
Q

Why are fluid filled lungs more compliant than air filled lungs?

A

Partly due to surface tension
Air-water interface exhibits surface tension
Fluid-water interface does not

29
Q

What type of cell produces surfactant?

A

Type II Pneumocyte

30
Q

What is the role of surfactant?

A

It breaks up the water molecules, reduces surface tension
Increases compliance
Prevents alveolar collapse
Reduces the ‘work of breathing’

31
Q

How does cross sectional area change through the lung?

A

Massive increase due to bifurcations from generation 7/8/9

32
Q

Describe resistance as you go through the lungs (airway generations)

A

Resistance increases as tube decreases, but due to the increased cross-sectional area means it is spread so overall decreases

33
Q

Conductance

A

How well the airways will conduct and allow air to pass through.

34
Q

How do conductance and resistance change with increasing lung volume? Why does this happen?

A

Conductance increases and resistance decreases with increasing volume because when the lungs inflate, the airways dilate
(i.e. the radius increases).

35
Q

When does peak resistance occur?

A

Around the 4th generation

36
Q

What could become an issue in expiration? How is this prevented?

A

Can create such a positive pressure that the airway becomes occluded
Not ideal as transmural pressure becomes negative
We have cartilage so this is not an issue

37
Q

At rest, pressure in airways and lungs and pressure in intrapleural space at functional residual capacity

A

Airways and lungs: 0
Because of recoil of lung and chest wall:
Intrapleural space: -5
(as opposing forces create a partial vacuum)

38
Q

How does TLC change in obstructive and restrictive disease?

A

Obstructive: increases
Restrictive: decreases

39
Q

How does residual volume change in obstructive and restrictive disease?

A

Obstructive: increases
Restrictive: decreases

40
Q

How does the change in volume per unit pressure change as you move further from FRC?

A

Change in volume per unit pressure DECREASES as you move further from FRC

41
Q

What is the significance of the shape of the curve with regards to ease of tidal breathing?

A

Close to FRC, you get a large change in volume per unit pressure so we can relatively easily inspire and expire in tidal breathing. Further deviation from FRC, the more difficult it becomes to increase the volume.

42
Q

How does the volume-pressure curve change in obstructive and restrictive disease?

A

Obstructive: moves up
Restrictive: moves down

43
Q

Compliance, elastance and airway resistance in restrictive lung disease

A

Compliance: Decreases
Elastance: Increases
Airway resistance: No change

44
Q

FEV1/ FVC ratio, FEV1 and FVC in obstructive lung disease

A

FEV1/FVC ratio: decreases
FEV1: decreases
FVC: decreases

45
Q

FEV1/ FVC ratio, FEV1 and FVC in restrictive lung disease

A

FEV1/FVC ratio: increases
FEV1: decreases
FVC: decreases

46
Q

In which direction does air move?

A

Down a pressure gradient

From higher pressure to lower pressure

47
Q

Describe negative pressure breathing referring to the alveolar pressure and volume.

A

Respiratory muscles work to decrease intraalveolar pressure

Creates a pressure gradient between the alveoli and the atmosphere so air is drawn into the alveoli

Respiratory (21 decks)

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