Surfactant, compliance and lung function tests Flashcards
what is the function of surfactant?
it decreases the suface tension on the alveolar membrane thus reducing the tendency for alveoli to collapse
where does surface tension occur and what is it?
the boundary between air and water. It is the attraction between water molecules
what is the direction of the force caused by surface tension of water molecules arranged in a circle/sphere?
inwards
how does surfactant prevent the collapse of alveoli?
the surfactant molecules lie between water molecules around the inside of the alveoli, this reduces surface tension
what are the functions of surfactant?
- reduces surface tension to prevent alveoli collapsing.
- increases lung compliance
- reduces lung’s tendency to recoil
- makes work of breathing easier
- is more efficient in small alveoli so prevents air moving from small alveoli to larger ones.
explain the problem with alveoli of different sizes and how surfactant solves this
with out surfactant the inward pressure in smaller alveoli would be much higher than in larger alveoli, and so air would move from small to large alveoli. This is unfavourable as the surface area to volume ratio would decrease. sufactant combats this as it’s more concentrated in the smaller alveoli and rerduces the pressure in them more, equalising the pressure in all alveoli.
what is infant respiratory distress syndrome?
a condition that effects babies born very prematurely . they have not yet started to produce adequate amounts of surfactant so an immense amount of effort is required for them to breath to overcome the surface tension in their alveoli.
what is the difference between the effort required to inflate and deflate a lung in saline solution compared with air and why is this important for infant respiratory distress syndrome?
it requires a much greater increase in pressure to inflate a lung in air than in saline solution and a much greater decrease for deflation.
This means that when a baby is born it must use much more effort to breath even with surfactant, without surfactant it would be significantly more again.
what is compliance?
change in volume relative to change in pressure
what does compliance represent?
it represents stretchability (not elasticity)
what does a high compliance mean?
large increase in lung volume for small decrease in ip pressure
what does a low compliance mean?
small increase in lung volume for large decrease in ip pressure
describe how compliance will be altered with patients with emphysema
it will be normal as emphysema does not affect lung stretch, just recoil.
what is emphysema?
a break down of the elastic fibres around alveoli, it affects recoil of the lungs
what is fibrosis in the lungs?
the build up of fibrous tissue in the lungs around the alveoli
how does fibrosis affect compliance?
it causes it to decrease as it decreases stretch
how does compliance change with age?
it decreases
does it require a greater pressure change to maintain a volume during expiration or reach the same volume by inspiration? why?
reach the volume by inspiration. this is because the tissue inertia has to be overcome and so does the surface tension as surfactant conc. is low
what does a less steep line on a volume-pressure graph indicate about compliance?
lower compliance
what happens to alviolar ventilation moving from base to apex?
it decreases
what happens to compliance moving from base to apex of lung?
it decreases
why does compliance decreases moving from base to apex?
the alveoli at the base of the lungs are more compressed due to the weight of the lung above them, the alveoli at the apex are more inflated so a change in pressure causes less change in volume.
a change is intrapleural pressure will bring about the biggest change in which area of the lung?
the base
what is an obstructive lung disease?
the airways are obstructed, especially on expiration
what is a restrictive lung disorder?
the expansion of the lung during inspiration is restricted
what does an obstructive lung disorder do to the airways?
increases their resistance
give some examples of obstructive airway disorders?
Asthma
COPD eg. chronic bronchitis, emphysema
what is chronic bronchitis?
inflammation of the bronchi
what is emphysema?
destruction of elastic fibres and destruction of alveoli
what does a restrictive lung disorder do to the lungs?
causes loss of lung compliance: lung stiffness, incomplete lung expansion
what is fibrosis?
formation or development of excess fibrous connective tissue
what causes fibrosis?
asbestosis
idiopathic
which conditions are classified as restrictive airway disorders?
- fibrosis
- infant respiratory distress syndrome
- oedema
- pneumothorax
what is spirometry?
technique commonly used to measure lung function
what is a static spirometry reading?
where the only comsideration made is the volume exhaled
what is a dynamic spirometry reading?
where the time taken to exhale a certain volume is being measured
which volumes is the spirometer able to measure?
- tidal volume
- inspiritory reserve level
- expiratory reserve volume
- inspiratory capacity
- vital capacity
what is the FEV1/FVC in a normal person?
80%
how does FEV1/FVC differ from normal in a suffer of an obstructive airway disorder? why?
it is lower (than 80%).
rate of exhalation is much slower, so is total volume but major effect is on airways and so FEV is reduced to a greater extent than FVC
how does FEV1/FVC differ from normal in a suffer of a restrictive airway disorder? why?
it is the same or higher (than 80%).
Absolute rate of airflow is reduced
Total volume is reduced due to limitations to lung expansion
Ratio remains constant or can increase as a large proportion of volume can be exhaled in the first second
what is a limitation of spirometry?
the ratio obtained is not always enoug to indicate health particulary for restrictive pulmonary disorders. Absolute values are required to show ill-health
what is forced expiratory flow?
average expired flow over the middle of an FVC. 25% through FVC divided by 75% throuh FVC
what are the advantages and disadvantages of forced expiratory flow?
- Correlates with FEV1 but changes are generally more striking
- However “normal” range is greater
