Compliance and resistance lecture

Question 1

what are the determinants of elastic recoil of lungs (x2)

Answer 1

1. elastic property (elasticity) of the lung tissue: 1/3 elastic recoil accounted
2. surface tension in the lungs
   ST tends to collapse lungs

Question 2

role of surfactant molecule

Answer 2

1. reduce elastic recoil = increase compliance (reciprocal relationship) = reduce work of breathing

2.Alveolar pressure stabilised (laplaces law)
P=2T/r

3.Prevent fluid sucked into lungs = prevent lung odema

Question 3

determinant of chest wall recoil pressure

where is natural position at

Answer 3

elastic nature of the chest wall

natural position at 60% vital capacity

Question 4

what is special about FRC

Answer 4

1. no air flow because PA=PB
2. equal and opposite recoil pressure of lungs and chest wall
   = natural position of the respiratory system

Question 5

compliance definition and draw the graphs

Answer 5

the pressure needed to change lung volume
Vol/pressure

reciprocal relationship with elasticity

Question 6

what is the relationship between pressure, air flow and resistance

Answer 6

Flow: Pressure/resistance

Question 7

factors that increases resistance

Answer 7

1. airway diameter (exponential)= r4
   2.turbulent flow, determined by air velocity
   3.air density (aka air pressure) = deep dive
   4.bronchomotor tone: neural, inflammatory mediator, hypoxia
   5.radial traction of the lungs when expanded (recoil pressure = radial traction)
2. pathologies: asthma, obstruction (COPD), fibrosis
3. transmural pressure: Pin-Pout = Paw-Ppl
   explain asthma

Question 8

distribution of resistance

Answer 8

largest in upper airway, lowest in lower airway due to extensive branching

Question 9

2 components of work of breathing

Answer 9

elastic forces (compliance related)
resistive forces

Question 10

Pattern of breathing and work of breathing relationship

Answer 10

ventilation = frequency (15 normal) x tidal volume (0.5L) normal

to maintain ventilation (aka constant)

1. hyperventilation = increase respiratory frequency
   - > reduce tidal volume

= reduced lung volume = reduced radial traction: increase resistance
= reduced lung volume = reduce elastic recoil = increase compliance

opposite for reduced ventilatory rate

patients with INCREASE/DECREASE rate of breathing: increase work of breathing

Question 11

5 factors that affect lung compliance

Answer 11

1. lung volume it self
2. age and lung size (adult more compliant)
3. diseases presence: odema, emphysema, fibrosis
4. posture: supine reduces compliance: diaphragm domed, pressure from pulmonary circulation
5. pulmonary vascular congestion leading to interstitial odema

Question 12

3 factors that affects lung compliance

Answer 12

1. rib cage deformation: morbid obesity, kyphoscoliosis
2. respiratory muscle diseases: intercostal muscles
3. posture: stand up more compliant: diaphragm is part of chest wall