Mechanics Of Breathing And Gas Exchange Flashcards
What is the term for the stretchiness of the lungs?
Compliance
Give some features of lung fibrosis
Low compliance, stiff lungs Exposed to asbestos/coal dust Collagen laid down Stops elastin moving Lungs cannot fill very much
Give some features of emphysema
Loss of elasticity, high compliance
More air into lungs
No elastic recoil as elastin has been destroyed by elastases
Expiration is difficult
Give some factors that decrease lung compliance
Laying supine/prone
Laparoscopic surgical interventions (increased abdo pressure)
Severe restrictive pathologies
Hydrothorax (pleural effusion)
Pneumothorax
High standing of diaphragm (obesity, pregnancy)
What is surface tension?
The water molecules of the lining fluid of the lungs attract each other (H bonds)
The interface of air and fluid makes the surface resistant to stretching
(Why we need surfactant)
Why do we need lining fluid in the lungs?
To be able to move gases
Why do we have surfactant in the lungs?
To reduce the surface tension
Is a detergent that interrupts the H bonds
Makes the alveoli easier to inflate
What are the constituents of surfactant?
90% phospholipids
Phosphatidylglycerol
Protein
Where is lung surfactant produced?
Type 2 pneumocytes
Simple cuboidal epithelial cells
Surfactant works better for: bigger or smaller breaths?
Smaller
Quiet breathing uses less energy
What is Laplace’s law for working out the pressure inside a bubble?
Pressure = (2 x surface tension) / radius
Define the law of bubbles
If a big bubble is connected to a small bubble, air will flow from the higher pressure (small bubble) into the lower pressure (big bubble). Therefore the small bubble will collapse into the big bubble.
How does surfactant help to keep alveoli open?
Equalises the pressure between different sized alveoli so that they do not collapse into each other
Define atelectasis
Parts of the lung collapsing
Describe infant respiratory distress syndrome
Babies born prematurely (<36 weeks) have too little surfactant
Lungs are very stiff
Few, very large alveoli
Surfactant is dripped into the lungs and the baby is put on a low pressure ventilator
Why don’t you put the infants with RDS on a high pressure ventilator?
Would cause the lungs to rupture or pneumothorax
Describe adult RDS
Not due to a lack of surfactant
Usually trauma
More difficult to treat because of the widespread inflammation in the lungs
What different factors are taken into account in Fick’s first law of diffusion?
Pressure difference Solubility of gas in solution Cross sectional area of fluid Distance molecules most travel Molecular weight of the gas Temperature of the fluid
How much more soluble in CO2 than O2?
20x more soluble
The diffusion coefficient is proportional to:
Solubility / square root of molecular weight
What is the equation for permeability?
(Diffusion coefficient x solubility) / thickness of the membrane
At 37’C what is the partial pressure of H2O in inspired air?
6.26 kPa
What happens to carbon dioxide when it enters the RBCs?
Reacts with water to form carbonic acid
Dissociates to form bicarbonate ions and H+ ions
Bicarbonate moves into plasma
H+ buffered by Hb
How is carbon dioxide carried in the blood?
90% carried as bicarbonate ions in the plasma
5% carried as dissolved CO2 in plasma
5% carried as carboxyhaemoglobin on proteins
