Respiratory Mechanics

Inspiration
Diaphragm contracts and flattens causing an increase in negative intrathoracic pressure resulting in air moving into the lungs. When abdominal compliance is reached, the lower ribcage expands.

Expiration
Largely passive with elastic recoil as the driving pressure. Airways are narrower during expiration than inspiration, which makes expiration more difficult and provides a transition between inspiration and expiration.

Alveolar Pressure = inside lung, negative on inspiration, positive on expiration.

Transpulmonary Pressure = pressure difference in and out of lung

Pleural Pressure = pressure in pleural space, typically negative because of the inward pull of lung recoil and outward pull of chest wall recoil. 
End expiratory pleural pressure = 2cmH2O
End inspiratory pleural pressure = -6cmH2O

Pneumothorax neutralises pleural pressure so lung recoil is unopposed.
Emphysema leads to an increase in chest wall recoil resulting in hyperinflation.

Compliance = ease of inflation
                  = change in volume
                    change in pressure