13. Lung mechanics Flashcards by Georgia Leggett

Flow volume loop: Downward deflection

Inspiratory

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Flow volume loop: Upward deflection

Expiratory

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How to calculate L per minute

L per s X 60

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Flow volume loop: Outer lines

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

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Flow volume loop: little loop in middle

Tidal volume

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Flow volume loop: left and right on the x axis

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

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Where is lung volume higher on Flow volume loops?

Where the axis cross

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Flow volume loop: mild COPD

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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Flow volume loop: severe COPD

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

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Flow volume loop: Restrictive disease

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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Flow volume loop: variable extra thoracic obstruction

Normal Expiratory curve

Inspiratory curve is blunted: still getting air in but limited

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Flow volume loop: variable intrathoracic obstruction

Normal inspiratory curve

Blunted expiratory curve

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Flow volume loop: Fixed airway obstruction

Both inspiratory and expiratory curves are blunted

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Describe obstructive lung disease

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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Describe restrictive lung disease

Inflation/ deflation of lung or chest wall is restricted

Lungs operating at lower volumes

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Chronic causes of obstructive lung disease

COPD:
Empysema
Bronchitis

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Acute causes of obstructive lung disease

Asthma

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Pulmonary causes of restrictive lung disease

Lung fibrosis

Interstitial lung disease

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Extrapulmonary causes of restrictive lung disease

Obesity

Neuromuscular disease

Summarise values in COPD

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

Summarise values in restrictive lung disease

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

Shape of transrespiratory system pressure

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

Transrespiratory system pressure curve in restrictive disease

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)

Transrespiratory system pressure curve in obstructive disease

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

Compliance

Tendency of a structure to distort under pressure | Change in volume / change in pressure

Elastance

Tendency of a structure to recoil to its original volume | Change in pressure / change in volume

Compliance, elastance and airway resistance in obstructive lung disease

Compliance: Increases Elastance: Decreases Airway resistance: Increases

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

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

What type of cell produces surfactant?

Type II Pneumocyte

What is the role of surfactant?

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

How does cross sectional area change through the lung?

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

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

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

Conductance

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

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

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

When does peak resistance occur?

Around the 4th generation

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

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

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

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

How does TLC change in obstructive and restrictive disease?

Obstructive: increases Restrictive: decreases

How does residual volume change in obstructive and restrictive disease?

Obstructive: increases Restrictive: decreases

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

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

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

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.

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

Obstructive: moves up Restrictive: moves down

Compliance, elastance and airway resistance in restrictive lung disease

Compliance: Decreases Elastance: Increases Airway resistance: No change

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

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

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

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

In which direction does air move?

Down a pressure gradient | From higher pressure to lower pressure

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

Respiratory muscles work to decrease intraalveolar pressure | Creates a pressure gradient between the alveoli and the atmosphere so air is drawn into the alveoli