This is the amount of air remaining in the lungs after performing a maximal expiration. Normal expiration occurs naturally and takes roughly 500mls, however when patients exhale more than normal, the air volume remaining in the lungs is referred to as the residual volume (Hyatt & Scanlon, 2014). The residual volume cannot be measured, but it can be determined by subtracting the Functional Residual Capacity (FRC) from the Expiratory Reserve Volume (ERV). In some cases, patients with obstructive lung disease who are unable to completely empty their lungs may experience a considerable rise in residual volume. FRC is the amount of air that remains available in the lungs after making a passive expiration (Broaddus & Mason, 2015). The FRC is an important lung volume parameter that provides an adequate respiratory air volume for the subsequent respiration. It also proves to be physiologically important for opening the small airways, thus preventing the complete emptying of the lungs during the end of every expiration. The FRC provides the ease of diffusion of the respiratory gases through the maintenance of the variation of the alveolar PCO2 and PO2. This parameter can be measured by the sum of the Expiratory Reserve Volume and the Residual Volume.
Total Lung Capacity
This is the total amount of respiratory air that can be contained in the lungs after a complete respiratory inhalation. The amount of air contained under a total lung capacity includes the tidal volume, inspiratory reserve volume, expiratory reserve volume, and the residual volume (Broaddus & Mason, 2015).
Inspiratory Reserve Volume
This is the extra volume of air that can be inhaled by maximal effort after reaching a normal and quiet inspiration (Hyatt & Scanlon, 2014). IRV is the volume of air that can be inhaled after a normal inhale has been made. For men and women, this air approximately measures about 3100mls and 2400mls respectively. It varies with exercise, where a person who exercises often enhances the inspiratory reserve capacity. The inspiratory reserve volume is measured by the difference between the maximum inspiration volume and the maximum tidal volume.
Expiratory Reserve Volume
This is the maximum amount of air volume that can be expired forcibly beyond the normal tidal expiration (Hyatt & Scanlon, 2014). This amount of reserve air, which is approximately about 1000mls that are forcefully exhaled after making a normal expiration. This form of air volume is an essential parameter during the pulmonary function test that can assist in identifying pulmonary diseases. For patients that experience respiratory disorders, the expiratory reserve volume may be reduced due to minimal respiratory inhalation. The ERV can be measured by a spirometer, and its calculations can be derived by the subtraction of the Functional residual capacity and the residual volume.
Disorders that can alter the Residual volume
The three diseases that can lead to the alteration of the residual volume include chronic bronchitis, asthma, and chronic obstructive pulmonary disease. Chronic bronchitis is an irritation and inflammation of the lung airways (Sinha & Singh, 2014). When the airways are inflamed, a thick mucus begins to form thus hindering difficulty and reducing the volume of the residual capacity. Asthma is the difficulty in breathing caused by triggers, which may be indoors triggers or outdoors triggers (Sinha & Singh, 2014). A person with asthma experiences difficulties in breathing thus reducing the amount of residual volume. COPD is a respiratory disease that affects the lungs and other parts of the bodies. It is characterized by the limitation of airflow both inward and outward, thus limiting the amount of residual volume (Jarenba\u0308ck & Linnea 2013).
References
Broaddus, V. C., & Mason, R. C. (2015). Murray & Nadel's Textbook of Respiratory Medicine. London: Elsevier Health Sciences.
Hyatt, R. E., & Scanlon, P. D. (2014). Interpretation of pulmonary function tests: A practical guide. Philadelphia: Wolters Kluwer Health.
Jarenbäck, & Linnea. (2013). Flow-Volume Parameters in COPD Related to Extended Measurements of Lung Volume, Diffusion, and Resistance. Hindawi Publishing Corporation.
Sinha, A., & Singh, S. (2014). Overview on Anatomy of Human Respiratory System. Human Respiratory Viral Infections, 3-16. doi:10.1201/b16778-3
