Respiratory System Breathing Mechanism: Respiratory Volumes and Capacity, Alveolar Ventilation, and Nonrespiratory Movements

Respiratory Volumes The different volumes of air that enter or leave the lungs – Can be divided into four different volumes: Resting tidal volume Inspiratory reserve volume Expiratory reserve volume Residual volume

Spirometry Study of respiratory volumes

Spirometer Used to measure respiratory air volumes (except residual volume) – These volumes can then be used in the evaluation of respiratory illnesses

Respiratory Cycle One inspiration and one expiration

Tidal Volume Volume of air that enters or leaves during a respiratory cycle

Resting Tidal Volume Volume of air that enters or leaves during normal, resting inspiration and expiration – About 500 mL

Inspiratory Reserve Volume Volume of air taken in during forced maximal inspiration in addition to the resting tidal volume – Equals about 3,000 mL

Expiratory Reserve Volume Volume of air expelled from the lungs during maximal forced expiration in addition to the resting tidal volume – About 1,100 mL

Residual Volume Air that remains in the lungs – (About 1,200 mL even after the most forceful expiration) Mixes with newly inhaled air – Prevents the CO 2 /O 2 concentrations from fluctuating greatly with each breath

Vital Capacity The maximum volume of air a person can exhale after taking the deepest breath possible Equal to tidal volume plus inspiratory reserve volume plus expiratory reserve volume – About 4,600 mL

Inspiratory Capacity Maximum volume of air a person can inhale following a resting expiration Equal to the tidal volume plus the inspiratory reserve – About 3,500 mL

Functional Residual Capacity Volume of air that remains in the lungs following a resting expiration Equal to the expiratory reserve volume plus the residual volume – About 2,300 mL

Total Lung Capacity Equal to the vital capacity plus the residual volume – About 5,800 mL – Total varies with gender, age, and body size

Anatomic Dead Space Created by air that is inspired (about 150 mL) but remains in the trachea, bronchi, and bronchioles where gas exchange does not occur

Alveolar Dead Space Created by nonfunctional air sacs (due to poor blood flow in adjacent capillaries)

Physiological Dead Space Total volume of the anatomical dead space and the alveolar dead space – Volume is essentially the same as the volume of the anatomical dead space (about 150 mL)

Minute Ventilation Volume of air moves into the respiratory passages each minute Equal to the tidal volume multiplied by the breathing rate Much of this new air remains in physiological dead space

Alveolar Ventilation Rate Volume of new air that reaches the alveoli and is available for gas exchange Equal to (the tidal volume minus the physiological dead space) multiplied by the breathing rate – (500 mL – 150 mL) x 12 breaths/min = 4,200 mL/min

Nonrespiratory Air Movements Air movements that occur in addition to breathing Used to clear air passages or to express emotions Usually result from reflexes but can also be triggered through conscious effort

Coughing Used to clear the lower respiratory passages Involves: – Taking a deep breath – Closing the glottis – Forcing air upward from the lungs against closure – Suddenly opening the glottis – And forcing a blast of air upward from the lower respiratory tract

Sneezing Clears the upper respiratory passages Usually triggered by an irritant in the lining of the nasal cavity Similar to a cough but in the process of sneezing the uvula is depressed directing the upward forced air to enter the nasal passages

Laughing Involves a person taking a breath and releasing it in a series of short expirations

Crying Works through the same process as laughing

Hicupping Caused by a sudden inspiration due to a spasmodic contraction of the diaphragm while the glottis is closed Associated noise is caused by air striking the vocal cords Function of hiccups is not known

Yawning A deep inspiration that involves the glottis and mouth being open Why we yawn and why it is “contagious” are not understood