Physiology first internal solution

 Define compliance. What is its significance? What are the factors that influence compliance? 

Definition: The change in lung volume per unit change in transpulmonary pressure.

Normal value: 0.22 l/cm H2O

Factors that influence compliance:

- Surface tension

- Lung volume

- Phase of respiratory cycle

- Effect of gravity

 Significance:

 Compliance is increased in emphysema & old age, decreased in pulmonary congestion,

 pulmonary fibrosis & pulmonary edema 

Pneumothorax

- refers to presence of air in the pleural space

Cause: Either through a rupture in the lung or a hole in the chest wall (stab injury, gun shot

 wound etc.,)

Types:

 a) Open or sucking pneumothorax

 b) Closed pneumothorax

 c) Tension pneumothorax

Open or sucking pneumothorax:

 The communication between the pleural space and the exterior remains open

Closed pneumothorax:

 Hole through which the air enters the pleural space is sealed off.

Tension pneumothorax:

 A flap of tissue lies over the hole in the lung or chest wall acts as a valve. This will allow

 air to enter the pleural space during inspiration but does not allow air to exit during

 expiration.

Features:

- Collapse of lung on affected side (As the pleural pressure becomes positive, the

elastic recoil of lungs leads to collapse)

- Mediastinum shifted towards normal side

- Respiratory distress (due to stimulation of respiratory centers by hypoxia and

hypercapnia)