13. Lung mechanics Flashcards
Flow volume loop: Downward deflection
Inspiratory
Flow volume loop: Upward deflection
Expiratory
How to calculate L per minute
L per s X 60
Flow volume loop: Outer lines
Respiratory flow envelope
No matter how hard you try you can’t go beyond those bounds
Anatomical limitation
Flow volume loop: little loop in middle
Tidal volume
Flow volume loop: left and right on the x axis
Left: Higher lung volume (total lung capacity)
Right: Lower lung volume (residual volume)
Where is lung volume higher on Flow volume loops?
Where the axis cross
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
Flow volume loop: severe COPD
Shorter curve (peak expiratory flow decreases)
Displaced to the left
Coving is much more severe
Narrower (Vital capacity decreases)
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
Flow volume loop: variable extra thoracic obstruction
Normal Expiratory curve
Inspiratory curve is blunted: still getting air in but limited
Flow volume loop: variable intrathoracic obstruction
Normal inspiratory curve
Blunted expiratory curve
Flow volume loop: Fixed airway obstruction
Both inspiratory and expiratory curves are blunted
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
Describe restrictive lung disease
Inflation/ deflation of lung or chest wall is restricted
Lungs operating at lower volumes
Chronic causes of obstructive lung disease
COPD:
Empysema
Bronchitis
Acute causes of obstructive lung disease
Asthma
Pulmonary causes of restrictive lung disease
Lung fibrosis
Interstitial lung disease
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
