Lecture 20 – The Mechanics of Breathing II

Question 1

Ohms law 2

Answer 1

P

Question 2

Hagen-Poiseuille 1

Answer 2

P

Question 3

Decrease in airflow 3

Answer 3

P

Question 4

Decrease in airflow - pattern of airflow 2

Answer 4

P

Question 5

Decrease in airflow - airway patency 4

Answer 5

P

Question 6

Spirometry 5

Answer 6

Measures FEV1/FVC ratio.
Quantifies airflow and the level of airway obstruction present during breathing.
Patients produce max forced expiration into spirmoeter which meausres air passing through over time.
FEV1 = Max volume that can be expired during the first second of maximum forced expiration.
Decimal or percentage.

Question 7

Spirometry - why may value differ 2

Answer 7

Obstructive airway diseases (asthma/chronic bronchitis), indicated by a reduction in FEV1 (<80% expected value), and FEV1/FVC ratio (<70%), IN resistance.
Restrictive lung diseases (pulmonary fibrosis), a reduction in FEV1 and FVC (<80% expected value), with a relatively normal FEV1/FVC ratio (>70%, i.e. the decrease in FEV1 reflects an overall decrease in lung volume rather than airway obstruction). DE compliance.

Question 8

Transpulmonary pressure 3

Answer 8

• Transpulmonary pressure- The level of force acting to expand the lung.
• Difference between the pressure within the alveoli and intrapleural space (Ptp = Palv – Pip). Ptp > 0 = expand. < 0 = compress.
• Lung pathology e.g. density of elastic and structural fibres such as elastin and collagen.

Question 9

Lung compliance 4

Answer 9

Compliance = Change in Volume/ Change in Pressure
• Lung compliance = the change in lung volume produced by a particular changed in transpulmonary pressure.e.g. compliance can therefore be thought of easily the lungs expand (much pressure change is required).
• Higher lung compliance = less elastic recoil = less force required to inflate = ↑ volume change per pressure change (↑gradient on volume-pressure curve).
• Lower compliance = more elastic recoil = more force required to inflate = ↓volume change per pressure change (↓ gradient on volume-pressure curve).

Question 10

Graphs 4

Answer 10

• Graph of lung volume vs. transpulmonary pressure, as lung compliance = the gradient of the curve.
• Static compliance (measurements taken whilst airflow =0), the steepest part of the curve is used.
• Dynamic compliance (measurements taken in the presence of airflow), the gradient between the end tidal inspiratory and end tidal expiratory points is used.
Both airway resistance and complaince can affect pressure-volume loops, the area within the loop is proportional to airway resistance generated.

Question 11

Lung compliance - diseases 5

Answer 11

Increase
COPD ( Elastin fibres)
Emphysema - elastin degradation

Decrease
Scoliosis/Muscular dystrophy/Obesity - chest wall mechanisms
Fibrosis - scarring + deposition of collagen,lung - elastin is stiff

NRDS- Alveolar surface tension

Question 12

Alveolar surface tension and the role of surfactant 7

Answer 12

P

Question 13

NRDS 4

Answer 13

• Occurs in infants born prematurely, and who develop and produce insufficient levels of pulmonary surfactant (at week 24-28).
• Results in respiratory failure due to the alveoli collapsing, IN lung compliance (‘stiffer’ lungs), and alveolar oedema DE gas exchange.
• Increasing force damages alveoli/capillaries.
• Treated by supplementation of affected infants with artificial surfactant, and/or by administering glucocorticoids (which increase surfactant production via maturation of type 2 pneumocytes) to mothers deemed high risk (e.g. mothers with poor diabetic control – insulin appears to affect pneumocyte maturation - or those at risk of premature birth).