This chapter focuses on the elastic properties of the respiratory system and on
the mechanisms by which gases are flown in and out of the lungs during the breathing
cycle. It begins by defining the lung volumes (capacities) and describing methods used
for measuring them. Then, it describes the mechanisms of inspiration and expiration and
the relationship between respiratory muscles and elastic characteristics of the respiratory
system. The properties of respiratory mechanics are then divided into two sections: static
and dynamic. Static mechanics deals with elastic characteristics of lungs, chest wall and
the combined lungs + chest wall system, and with methods used for quantifying them.
The relevance of surface tension and surfactant in modulating lung compliance and in
maintaining the alveoli dry is discussed in detail. Dynamic mechanics discusses how
gases flow through airways during the breathing cycle. Alveolar and intra-pleural
pressures changes during normal breathing and while breathing through narrowed
airways are described, as well as mechanism causing airway collapse in patients with loss
of lung elasticity (emphysema), or suffering from extra-thoracic airway obstruction. The
last two sections deal with the work of breathing and the most common pulmonary
function tests.
Keywords: Airway Collapse, Airway Resistance, Bernoulli Principle, Breathing
Cycle, Chest-Wall Compliance, Diaphragm, Elastance, Expiratory Muscles,
Inspiratory Muscles, Intercostal Muscles, Laminar Flow, Lung Compliance, Lung
Volumes, Plethysmography, Pulmonary Function-Tests, Respiratory Work,
Spirometry, Surface Tension, Surfactant, Trans-Pulmonary Pressure, Turbulent Flow.
