Pulmonary Ventilation and Breathing Process

Pulmonary Ventilation

• Pulmonary ventilation, also known as breathing, is the process of air flowing into the lungs during inspiration and out of the lungs during expiration.
• Air flows due to pressure differences between the atmosphere and the gases inside the lungs, moving from higher to lower pressure.

Pressures Involved in Ventilation

• Atmospheric pressure: the pressure of the air outside the body.
• Intraalveolar pressure: the pressure inside the alveoli of the lungs.
• Intrapleural pressure: the pressure within the pleural cavity.

Inspiration

• Inspiration (inhalation) is the active phase of ventilation, resulting from muscle contraction.
• During inspiration, the diaphragm contracts, increasing the thoracic cavity volume, which decreases intraalveolar pressure, allowing air to flow into the lungs.

Expiration

• Expiration (exhalation) is the process of letting air out of the lungs during the breathing cycle.
• During expiration, the relaxation of the diaphragm and elastic recoil of tissue decreases the thoracic volume and increases intra-alveolar pressure, allowing air to flow out of the lungs.

Pulmonary Volumes and Capacities

• The average adult takes 12 to 15 breaths per minute, with one breath consisting of one inspiration and one expiration.
• A spirometer is used to measure the volume of air moving into and out of the lungs (spirometry).
• Respiratory volumes and capacities can provide information about the physical condition of the lungs.

Lung Volumes

• Measurable lung volumes using a spirometer include:
  • Tidal volume (TV)
  • Expiratory reserve volume (ERV)
  • Inspiratory reserve volume (IRV)
• Residual volume (RV) is the amount of air left in the lungs after a forced exhalation and can only be calculated.

Lung Capacities

• Calculated lung capacities include:
  • Vital capacity (ERV+TV+IRV)
  • Inspiratory capacity (TV+IRV)
  • Functional residual capacity (ERV+RV)
  • Total lung capacity (RV+ERV+TV+IRV)