Lung compliance

Question 1

factors affecting change in transpulmonary pressure

Answer 1

stretchability/compliance of lungs

Question 2

lung compliance definition and equation

Answer 2

magnitude of change in lung volume produced by a given change in transpulmonary pressure
= change in lung volume/change in transpulmonary pressure
greater the lung compliance, the easier it is to expand lungs at any given change in transpulmonary pressure

Question 3

low lung compliance

Answer 3

greater than normal transpulmonary pressure must be developed across the lung to produce a given amount of lung expansion - intrapleural pressure must be made more subatmospheric

Question 4

what does low lung compliance cause?

Answer 4

more vigorous contractions of the diaphragm and external intercostal muscles to reach the more subatmospheric intrapleural pressure - more energy required to produce a given amount of expansion
shallow and high frequency breathing

Question 5

determinants of lung compliance

Answer 5

stretchability of lung tissues/elastic connective tissues
(thickening of lung tissues decreases compliance)
surface tension at air-water interfaces within alveoli

Question 6

surface tension

Answer 6

attractive forces between the water molecules at the air-water interface
make water lining constantly shrink and resist further stretching

Question 7

what is the energy required for?

Answer 7

to stretch the connective tissue and to overcome the surface tension

Question 8

pure water

Answer 8

very high surface tension

if alveoli were lined with pure water, lung expansion would require exhausting muscular effort and lungs would collapse

Question 9

surfactant

Answer 9

detergent-like substance secreted by type 2 alveolar cells - reduces cohesive forces between water molecules - lowers surface tension and increases lung compliance

Question 10

surfactant contents

Answer 10

mixture of lipids and proteins
phospholipid inserts its hydrophilic end into water layer, and its hydrophobic ends form monomolecular layer between air and water at alveolar surface

Question 11

what increases/decreases amount of surfactant?

Answer 11

decreases when breaths are small and constant

increases when taking deep breaths, as it stretches type 2 cells and stimulates secretion.

Question 12

law of laplace

Answer 12

relationship between pressure, surface tension and alveolus radius
P = 2T/r
as the radius decreases, pressure increases

Question 13

surfactant and stabilisation of alveoli of different sizes

Answer 13

alters surface tension depending on surface area of alveolus
as an alveolus gets smaller, the surfactant molecules are less spread out - reduces surface tension
helps maintain pressure in smaller alveoli that’s equal to that in larger ones

Question 14

respiratory distress syndrome

Answer 14

deficient surfactant
surfactant synthesising cells too immature to function adequately
fetuses don’t require surfactant, as lungs are filled with amniotic fluid, and they receive oxygen from the maternal blood
inhales with strenuous effeorts - exhaustion, no breathing, lung collapse and death
mechanical ventilator and administration of natural or synthetic surfactant through trachea