Mechanisms and measures of pulmonary ventilation

Inspiration (Inhalation)

An active process where the diaphragm and external intercostal muscles contract. This expands the thoracic cavity, drops intra-alveolar pressure below atmospheric pressure, and draws air inward

Expiration (Exhalation)

A passive process during quiet breathing where muscles relax, elastic recoil of the lungs decreases chest volume, raises internal pressure above atmospheric pressure, and pushes air out. Forced expiration engages active abdominal and internal intercostal muscle contraction

Pressure Gradients

Airflow depends on the difference between atmospheric pressure and intra-alveolar pressure, regulated by changing intrapleural (negative) pressures

Compliance and Resistance

Lung compliance (stretchiness) and airway resistance determine how easily air flows into the respiratory tree. Surfactant lines the alveoli to reduce surface tension and prevent collapse

Tidal volume

The amount of air inhaled or exhaled in a normal breath(~500 mL)

Inspiratory Reserve volume (IRV)

The amount of air that can be inhaled after inspiring normally(~3000 mL)

Expiratory Reserve Volume (ERV)

The amount of air that can be expired after exhaling normally (~1100 mL)

Residual Volume

The amount of air remaining in the lungs after maximum expiration

Functional Residual Capacity

ERV+RV

Inspiratory Capacity

TV+IRV

Vital capacity

IRV+TV+ERV

Total lung capacity

IRV+ERV+TV+RV

Pulmonary ventilation

TV* respiratory rate (total amount of gas entering the lungs per minute)

Aveolar ventilation

(TV - dead space)* respiratory rate (the volume of gas per unit time that reaches the alveoli)

Dead space ventilation

Dead space * respiratory rate (the amount of gas per unit time that does not reach the alveoli)