pk 3 - Lung Mechanics - Surfactant & Resistance Flashcards
The distending pressure is generated by the ……… ……… forces of the lungs and chest wall - and the …….. determines volume at any given distending pressure
elastic recoil
compliance
What determines the elastic properties of the lung? x2
- surface tension (65-70%)
- composition of tissues and its shape
What determines the compliance of the chest wall?
- inherent rigidity and shape
The chest wall compliance depends on rigidity of the thoracic cage and on its shape. This is decreased by conditions such as…
arthritic spondylitis or kyphoscoliosis
spasticity or rigidity of thoracic or abdominal musculature
True or False? There are no diseases associated with an increase in chest wall compliance
True
Surface tension is a …………… force that must be overcome when the lungs are ……………..
collapsing
inflated
Smaller bubbles must have a greater internal pressure to keep them inflated and overcome the surface tension. Why can different size alveoli coexist in the lung? Which Law explains this?
alveoli interdependence, the tendency for one to collapse is prevented by the tendency for others not to collapse
Laplace’s Law
What calculations prove that it can’t just be normal interstitial fluid lining the lungs?
calculations using an air interstitial fluid interface in the lungs show a very high surface tensions, reducing compliance significantly and making breathing difficult, if not impossible
By how much does surfactant decrease surface tension?
10x
What is surfactant made up of?
45% = DPPC (phospholipid) 45% = other phospholipids 10% = proteins, cholesterols and trace amounts of other substances
Which compound present in surfactant is responsible for lowering surface tension? By which cells is this secreted?
DPPC
alveolar Type II epithelial cells
The presence of a natural surface-acting detergent (…………..) acts to reduce ………….. ………….. and so …………. lung compliance
surfactant
surface tension
compliance
What is DPPC?
How does it act?
dipalmitoyl phophatidylcholine
palmitate is hydrophobic, phosphate and choline are hydrophilic.
DPPC molecules line the air liquid interface.
They reduce surface tension by preventing water molecules coming into contact with the air liquid interface
As surface area is reduced, the surface tension lowering effects of surfactant …………… .
Area dependent effect - the smaller the radius, the …… the density of DPPC and thus the ……. surface tension lowering effect.
This is the mechanism underlying the ………. observed when lugs are fully inflated and then deflated.
increases
greater
greater
hysteresis
What is hysteresis?
If you inflated the lung and measure pressure-volume the curve moves on a different trajectory to when you deflate the lung.
Give examples of disease/s that increase lung compliance?
Give examples of disease/s that decrease lung compliance?
emphysema
pulmonary fibrosis, congestion, RDS
Infant Respiratory Distress Syndrome:
- Why does a foetus not require surfactant?
- At what gestation does surfactant appear?
- What are the main factors that cause infants to be born with lack of surfactant?
- What are the consequences of low surfactant?
- How can lung maturity be assessed in utero?
- What is the treatment for lack of surfactant, in utero?
- What can be done to help infants who develop RDS after birth?
- no air liquid interface
- from 25-weeks, reaching high cons by 32-36 weeks
- maternal diabetes mellitus and prematurity
- low lung compliance, small alveoli collapse, infants become hypoxic, hypercapnic, acidotic and exhausted
- assay for phosphatidyl cholines
- give glucocorticoids
- instill surfactant into trachea
What is adult respiratory distress syndrome?
caused by damage to the alveolar-capillary interface and to alveolar Type II cells
associated with a large number of disorders e.g. pneumonia, sepsis, smoking
Airflow resistance is defined as…..
the pressure difference required for a given flow
What is the most common cause of ventilatory impairment?
increase in airway resistance caused by asthma
Extra work is required to overcome resistance. Resistance is made up of two components. What are they?
Airway resistance - resistance to flow by friction in the airways
Viscous resistance - resistance to flow by lung tissue friction
Total airflow resistance is normally …… but can be considerably ……… by …………. in airway calibre as described by …………….. Law.
low
increased
reduction
Pouiselle’s
Anything that reduces the airway ………. will ………. the work of breathing. this can occur through a variety of means and is either reversible or irreversible. A number of drugs are targeted at the physiological mechanism that control airway …..
diameter
increase
tone
Where is the greatest airway resistance found?
In the upper airways
Lowest total cross sectional area
What conditions increase upper airway resistance?
intraluminal airway obstruction
aspiration of foreign material
regurgitation of gastric contents or blood
bronchospasm
What condition increases lower airway resistance?
COPD
What physiological mechanism causes bronchoconstriction?
increase vagal parasympathetic activity, also induces mucus secretion
local chemical mediators e.g. histamines, leukotrienes
decreased airway CO2
What causes bronchodilation?
activation of B2 adrenoreceptors by adrenaline or sympathomimetics
non-adrengergic, non cholingergic (NANC) innervation
