Respiratory Volumes and Capacities
In normal quiet breathing, there are about 15 complete respiratory cycles per minute. The lungs and air passages are never empty, and the portion of the respiratory system not involved in gas exchange is called the anatomical dead space (about 150 mL).
Tidal Volume (TV)
The amount of air inhaled and exhaled during each breathing cycle, approximately 500 mL at rest.
Inspiratory Reserve Volume (IRV)
The extra volume of air that can be inhaled during maximal inspiration, above the normal tidal volume.
Inspiratory Capacity (IC)
The maximum amount of air that can be inspired with full effort. It is the sum of tidal volume and inspiratory reserve volume.
Functional Residual Capacity (FRC)
The amount of air remaining in the lungs and air passages at the end of quiet expiration. This volume helps prevent alveolar collapse and maintains continuous gas exchange.
Expiratory Reserve Volume (ERV)
The largest volume of air that can be expelled from the lungs during maximal expiration.
Residual Volume (RV)
The volume of air remaining in the lungs after forced expiration. It cannot be directly measured.
Vital Capacity (VC)
The maximum volume of air that can be moved into and out of the lungs during breathing.
Total Lung Capacity (TLC)
The maximum amount of air the lungs can hold, typically around 6 litres in an adult. TLC is the sum of vital capacity and residual volume.
Alveolar Ventilation
The volume of air that reaches the alveoli per minute, calculated as tidal volume minus anatomical dead space, multiplied by the respiratory rate. It ensures continuous gas exchange and is used in lung function tests to diagnose and monitor respiratory disorders.
Definitions
Resuscitation: Process of restoring breathing or heartbeat in an acutely unwell patient.
Hypoxia: A condition in which tissues are deprived of adequate oxygen supply.
Asphyxia: Extreme lack of oxygen and excess CO2 in the blood, causing suffocation.
Dysbarism: Decompression sickness caused by formation of excess gas bubbles in body tissues due to changes in pressure.
Oxygen Therapy: Treatment providing extra oxygen to improve tissue oxygenation.
Detailed Notes
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