Physiology · MU Sofia

36. Pulmonary ventilation. Pulmonary volumes and capacity Minute ventilation and alveolar ventilation.

Covers how air moves between atmosphere and lungs through pressure changes, and the muscles behind inspiration and passive expiration. Lists the four lung volumes and four capacities with approximate values, noting which cannot be measured by spirometry. Then explains minute ventilation and alveolar ventilation, including the dead space correction, and ends with recap questions.

Inside: 5 sections · 5 labelled pictures · 22 flashcards · 5 min

Topic 36 of 104 in the MU Sofia syllabus for Physiology (Medicine, Year 2). The free AceMed note covers it in 5 sections, about 646 words (5 min of reading), with 22 flashcards.

In this note

  1. Pulmonary ventilation. Pulmonary volumes and capacity Minute ventilation and alveolar ventilation.
  2. Pulmonary Ventilation
  3. Pulmonary Volumes and Capacities
  4. Minute Ventilation
  5. Alveolar Ventilation

Pulmonary Ventilation

  • Definition: Pulmonary ventilation refers to the process of air exchange between the atmosphere and the lungs. This exchange is driven by cyclical changes in the pressure gradient between the atmospheric pressure (Patm) and the alveolar pressure (Palv).
  • Mechanism: When Palv becomes negative relative to Patm, air flows from the atmosphere into the lungs (inspiration). Conversely, when Palv exceeds Patm, air is expelled from the lungs (expiration).
  • Muscles of Respiration: The diaphragm, the primary muscle of inspiration, contracts, increasing the thoracic cavity volume, which in turn reduces Palv. The external intercostal muscles and accessory muscles contribute to more forceful inspiration during exercise. Expiration is usually passive, relying on the elastic recoil of the lungs and chest wall.

Pulmonary Volumes and Capacities

Pulmonary volumes and capacities are routinely assessed using spirometry, a technique that measures the volume of air inhaled and exhaled.

Pulmonary Volumes:

  • Tidal Volume (TV): This represents the volume of air inspired during each normal breath. At rest, TV is approximately 500 mL.
  • Inspiratory Reserve Volume (IRV): This is the additional volume of air that can be forcefully inhaled after a normal inspiration. IRV is around 3,000 mL.
  • Expiratory Reserve Volume (ERV): This signifies the extra volume of air that can be forcefully exhaled after a normal expiration. ERV is about 1,200 mL.
  • Residual Volume (RV): This is the volume of air that remains in the lungs even after a maximal forced expiration. RV, approximately 1,200 mL, cannot be measured by spirometry and specialized techniques like helium dilution are required. This volume is crucial for preventing lung collapse.

Pulmonary Capacities:

Pulmonary capacities represent combinations of two or more lung volumes.

  • Total Lung Capacity (TLC): This is the total volume of air the lungs can hold after a maximum inhalation. TLC is the sum of all four lung volumes (TV + IRV + ERV + RV) and is approximately 6,000 mL.
  • Vital Capacity (VC): VC is the maximum volume of air that can be exhaled after a maximum inhalation. It is calculated as TV + IRV + ERV and is roughly 4,800 mL.
  • Inspiratory Capacity (IC): This represents the maximum volume of air that can be inhaled after a normal expiration. IC is calculated as TV + IRV, amounting to around 3,600 mL.
  • Functional Residual Capacity (FRC): This is the volume of air remaining in the lungs after a normal exhalation. FRC is the sum of ERV and RV, approximately 2,400 mL.

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