Overview
This lecture discusses the mechanics of breathing, focusing on pulmonary ventilation, pressure changes during the respiratory cycle, and related lung volumes and capacities.
Pulmonary Ventilation
- Pulmonary ventilation is the process of moving air into and out of the lungs.
- Inhalation (inspiration) draws air into the lungs; exhalation (expiration) expels air out.
- Inspiration is an active process requiring muscle contraction, mainly the diaphragm and external intercostals.
- Expiration is usually passive, resulting from relaxation of inspiratory muscles.
Pressure Changes During Breathing
- Air moves in or out of the lungs due to pressure gradients between the atmosphere and lung air spaces.
- Atmospheric pressure is the pressure exerted by air surrounding the body.
- Intrapulmonary pressure (alveolar pressure) is the pressure within the lung alveoli.
- Intrapleural pressure is the pressure within the pleural cavity, always lower than intrapulmonary pressure.
- During inspiration, thoracic cavity volume increases, decreasing intrapulmonary pressure and drawing air in.
- During expiration, thoracic cavity volume decreases, increasing intrapulmonary pressure and pushing air out.
Lung Volumes and Capacities
- Tidal volume (TV) is the amount of air inhaled or exhaled in a normal breath.
- Inspiratory reserve volume (IRV) is the additional air that can be inhaled after a normal inhalation.
- Expiratory reserve volume (ERV) is the extra air that can be exhaled after a normal exhalation.
- Residual volume (RV) is the air left in the lungs after maximal exhalation.
- Vital capacity (VC) is the total amount of exchangeable air (TV + IRV + ERV).
- Total lung capacity (TLC) is the sum of all lung volumes (TV + IRV + ERV + RV).
Key Terms & Definitions
- Pulmonary ventilation — movement of air into and out of the lungs.
- Intrapulmonary pressure — pressure within the alveoli of the lungs.
- Intrapleural pressure — pressure within the pleural cavity surrounding the lungs.
- Tidal volume (TV) — volume of air exchanged in a normal breath.
- Vital capacity (VC) — total amount of air that can be exhaled after maximal inhalation.
Action Items / Next Steps
- Review the definitions and relationships of all lung volumes and capacities.
- Practice labeling the phases and pressure changes during a typical respiratory cycle.