4 Compliance Flashcards
What do type 2 alveolar cells produce?
Surfactant, A detergent like fluid
What is the function of surfactant?
TO reduce surface tension on alveolar surface membranes. Thus reducin the chance they collapse.
What causes alveolar surface tension?
Attraction between surface molecules balances out with a net inward pull
How does surfactant affect compliance?
It increases compliance (distensibility) effectively making breathing easier
Where is surfactatn most effective?
On small alveoli because the surfactant molecules get closer & more concentrated.
Why is pressure greater in smaller alveoli?
P = (2 x surface tension)/radius
SMaller alveoli have a smaller radius & the same surface tension
When is surfactant produced?
Starts ~25 weeks
Complete by ~36 weeks
What surfactant related syndrome is often suffered by premature babies?
IRDS
Infant REspiratory Distress Syndrome
What stimulates surfactant production?
Thyroid hormones
Cortisol
Both increase towards end of pregnancy
What is compliance?
How much the lung volume changes for any given change in Ip pressure
What does high compliance mean?
The lung will have a large volume increase for a small intrapleural pressure decrease
How does compliance relate to elasticity & stretchability?
Compliance is a measure of stretchability (how easy the lung is to fill with air)
It doesnt tell you anthing about elasticity (how easily the air is pushed out)
Law of Laplace?
P = 2T/r
Tells us the inwardly directed pressure of the alveoli
What kind of alveoli collapse most easily?
Smaller alveoli because theyre inwardly directed pressure is the largest. Surfactant combats this
What hapens in IRDS?
No surfactant
Very high inward pressure in alveoli
So lots of small alveoli collapse between breaths
Makes it very hard to breath
What alveoli are most efficient?
The smaller ones because they have the largest surface area:volume ratio
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pasta
How does age affect compliance?
Compliance decreases over age
How do we determine compliance from graphically\?
Draw a graph of ip against lung volume with a curve for inspiration and one for expiration.
A straight line between them will give the value for compliance from its slope;
Why is a curve for inspiration less steep at the start?
At the start of inspiration the tissue inertia, elasticity and surface tension must be overcome.
Why is the curve for expiration less steep at the start?
compressing the chest to push out air also compresses the airways thus narrowing them.
Once the chest is quite compressed the pressure is high enough to overcome this and expiration curve steepens
What makes expiration passive
elastic recoil of lungs
What is emphysema?
Where tissue loses elasticity so expiration requires more effort and a larger increase in ip pressure to push out all the air
What is fibrosis?
excess inert fibrous connective tissue means inspiration requires more effort (decreases compliance)
How does compliance vary throughout a lung?
Greatest compliance at the base of the lung
Least compliance at the apex
Why does compliance vary though the lung?
Gravity
Alveoli at lung base are squashed by tissue above so are more empty at the end of expiration that the ones at the apex.
Therore on inspiration they are able to inflate more than the ones at the apex
This will vary with postion, if patient is lying down or upside down
What is an obstructive lung disease?
Increased airway resistance, especially on expiration.
Whats a restrictive lung disease?
Restriction of lung expansion
NAme some obstructive lung diseases?
Asthma
COPD - Chronic bronchitis
- Emphysema
What ahppens during a restrictive lung disorder?
The lung stiffens and has incomplete expansion
Name some restrictive lung disorders?
Fibrosis
IRDS
Oedema
Pneumothorax
What does asbestosis causes?
FIbrosis
What are the two types of spirometry?
Static or dynamic
Static spyrometry?
Only volume exhaled is measured
Dynamic spirometry?
Volume & time exhaled is emasured.
What values can be directly measuered by spirometry?
Tidal volume
Expiratory
Inspiratory capacity
What values can be determined by spirometry?
Inspiratory reserve volume
Vital capacity
What values cant be determined by spirometry?
Resiudal vlume
Functional residual capacity
What is the nomral forced expiratory volume in 1 second?
4L (adult male)
What is the normal forced vital capacity?
5L (adult male)
Therefore what is normal FEV1/FVC
80% (adult male)
How does an obstructive lun disease affect FEV1 & FVC?
FEV1 is massively reduced
FVC is only a little reduced
So FEV1:FVC drops
How does a restrictive lung disease affect FEV1 & FVC?
Reduced both but affects FVC more. usually.
The % is often the same or higher than normal.
What is FEF25-75?
The forced expiratory flow over the middle 50% of expiration
How does FEF differ to FEV1?
It correlates with FEV1 but with more striking changes, hence it can indicate early sigsn of lung disease.
However FEF has a wider normal range
