Mechanics of ventilation

Question 1

Describe compliance

Answer 1

The slope of the pressure volume curve, or the volume change per unit pressure change, is compliance.

Question 2

Name conditions causing a reduction in compliance

Answer 2

Pulmonary oedema
Fibrosis
Increase in pulmonary venous pressure

Question 3

Name conditions causing an increase in lung compliance

Answer 3

Emphysema
Age
Asthma attack

Question 4

Describe what happens to pressure volume curve when the lungs are filled with saline.

Answer 4

The saline filled lungs have much greater compliance because the saline abolished the surface tension so the exhalation curve is basically the same as the inhalation curve.

Question 5

What are the physiological roles of surfactant

Answer 5

1) Lowering surface tension increases compliance of the lung reducing the work of breathing
2) Stability of alveoli is promoted
3) Helps to keep the alveoli dry. In effect the surface tension in the alveoli reduces the hydrostatic pressure in the tissue outside the capillaries preventing transudation of fluid.

Question 6

Why are there topographical differences in the ventilation of the lung?

Answer 6

The lower regions of the lung ventilate more easily compared with the upper regions. Why- because due to gravity the lower region has lower (less negative) intrapleural pressures compared with the apex. the base of the lung has a larger change in volume and a smaller resting volume compared with the apex.