Mechanics of respiration and pulmonary ventilation
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Definition
Mechanics of respiration is the cyclical process by which contraction and relaxation of the inspiratory muscles generate the pressure gradients that drive air into and out of the lungs.
Airflow direction follows the sign of the alveolar-to-atmospheric pressure gradient, which reverses with each phase of the cycle.
Sequence of Events in Inspiration
Step 1 Diaphragm and other inspiratory muscles contract, expanding the thoracic cage; intrapleural pressure becomes more negative.
Step 2 The more negative intrapleural pressure raises transpulmonary pressure, inflating the lungs.
Step 3 Alveolar pressure falls subatmospheric, so air flows into the airways and lungs.
Step 4 Airflow into the lungs stops once alveolar pressure equalizes with atmospheric pressure.
Step 5 Inspiration ends with cessation of inspiratory muscle contraction.