lung compliance and resistance

Question 1

Properties of lung tissue

Answer 1

compliance (stretch), elasticity (recoil), resistance (friction), dynamic compression (collapse)

Question 2

Properties of lung tissue- lung compliance

Answer 2

how much work (pressure) is required to stretch (expand) the lungs. The lungs are compliant and therefore need very little change in pressure to generate inspiratory flow and cause change in volume.

Question 3

what does reduced lung compliance require

Answer 3

it requires the generation of a large pressure to change volume producing an increased respiratory workload

Question 4

Properties of lung tissue- elasticity

Answer 4

the ability of an object to return to its original shape and size (equilibrium position) after being stretched or compressed

Question 5

lung elasticity

Answer 5

in humans the lungs are always stretched above their equilibrium position and therefore are constantly try to collapse down, this is called elastic recoil. During inspiration a force is required to overcome the lungs elastic recoil and tendency to pull inwards in order to expand the lungs. when the force is removed the lungs recoil and gas is removed proving the force for expiration

Question 6

chest wall elasticity

Answer 6

the chest walls equilibrium position is larger than its position at rest. therefore the elastic properties of the chest wall are constantly trying to pull the chest wall outwards to resume its equilibrium position like a stress ball

Question 7

elasticity and normal breathing

Answer 7

the inward pull of the lungs is exactly balanced by the outward pull of the chest wall, which prevents the alveoli from collapsing, maintaining lung compliance. These 2 opposing elastic recoil forces also create the negative intrapleural pressure necessary for breathing to occur

Question 8

what is resistance

Answer 8

resistance is the force that must be overcome during breathing. Therefore with increased resistance a larger pressure change is required to initiate breathing

Question 9

what is airway resistance

Answer 9

it is the resistance of the respiratory tract to airflow during inspiration and expiration

Question 10

what is the amount of resistance is affected by

Answer 10

radius of the airway, lung volume, airway length, air flow pattern, viscosity of gas

Question 11

radius of the airway- where is resistance larger

Answer 11

resistance is larger in large airways because each large airway branches repeatedly the combined cross sectional area of the small airways is greater than the parent airway.

Question 12

factors affecting radius- bronchial smooth muscle

Answer 12

amount of bronchial smooth muscle- bronchoconstriction= narrowing the airways and increasing resistance, bronchodilation= widening of the airways and reducing airway resistance

Question 13

factors affecting radius- other

Answer 13

secretions, mucosal oedema, mass, inhaled foreign body

Question 14

pressure in and around the lungs during forced expiratory manoeuvre- alveolar pressure

Answer 14

pleural pressure is +20cm H20, the lung elastic recoil pressure another +10cm H20, both of these create the driving pressure which allows expiratory flow. This is alveolar pressure. The alveolar pressure progressively falls from the alveolus +30 to 0 at the mouth.

Question 15

pressure in and around the lungs during forced expiratory manoeuvre- as the pressure falls

Answer 15

as the pressure falls, at some point the pressure within the airways becomes equal to the pleural pressure (pressure outside the airway) this is known as the equal pressure point. Proximal to this point, towards the mouth airway pressure continues to fall below the plural pressure leading to dynamic compression and narrowing of the airway

Question 16

what is dynamic compression

Answer 16

Dynamic compression of the airways results when intrapleural pressure equals or exceeds alveolar pressure, which causes dynamic collapsing of the lung airways.