Nonrespiratory Air Movements

Total volume of air that the lungs can hold: TLC = VC + RV

* Values are typical for a tall, young adult.

* Values are typical for a tall, young adult.

In the microgravity environment of space, the gas exchange capacity of the alveoli increases by 28%. This is because blood flow in the pulmonary capillaries and ventilation of the alveoli are more uniform than on earth in the presence of gravity. Eight astronauts aboard two space shuttle missions provided this information by performing various pulmonary function tests. They worked in Spacelab, a small, cylindrical pressurized laboratory that is taken into space aboard the shuttle.

Nonrespiratory Air Movements

Air movements that occur in addition to breathing are called nonrespiratory movements. They are used to clear air passages, as in coughing and sneezing, or to express emotions, as in laughing and crying.

Nonrespiratory movements usually result from reflexes, although sometimes they are initiated voluntarily. A cough, for example, can be produced through conscious effort or may be triggered by a foreign object in an air passage.

Coughing involves taking a deep breath, closing the glottis, and forcing air upward from the lungs against the closure. Then the glottis is suddenly opened, and a blast of air is forced upward from the lower respiratory tract. Usually this rapid rush of air removes the substance that triggered the reflex.

A sneeze is much like a cough, but it clears the upper respiratory passages rather than the lower ones. This reflex is usually initiated by a mild irritation in the lining of the nasal cavity, and, in response, a blast of air is forced up through the glottis. This time, the air is directed into the nasal passages by depressing the uvula, thus closing the opening between the pharynx and the oral cavity.

Laughing involves taking a breath and releasing it in a series of short expirations. Crying consists of very similar movements, and sometimes it is necessary to note a person's facial expression in order to distinguish laughing from crying.

A hiccup is caused by sudden inspiration due to a spasmodic contraction of the diaphragm while the glottis is closed. Air striking the vocal folds causes the sound of the hiccup. We do not know the function, if any, of hiccups.

Yawning may aid respiration by providing an occasional deep breath. During normal, quiet breathing, not all of the alveoli are ventilated, and some blood may pass through the lungs without becoming well oxygenated. This low blood oxygen concentration somehow triggers the yawn reflex, prompting a very deep breath that ventilates more alveoli.

Table 19.5 summarizes the characteristics of nonrespiratory air movements. Clinical Application 19.3 discusses respiratory problems that affect ventilation.

The most sensitive areas of the air passages are in the larynx, the carina, and in regions near the branches of the major bronchi. The distal portions of the bronchioles (respiratory bronchioles), alveolar ducts, and alveoli lack a nerve supply. Consequently, before any material in these parts can trigger a cough reflex, it must be moved into the larger passages of the respiratory tract.

How is the minute ventilation calculated? The alveolar ventilation rate?

Which nonrespiratory air movements help clear the air passages?

Which nonrespiratory air movements are used to express emotions?

What seems to be the function of a yawn?

Shier-Butler-Lewis: I V. Absorption and I 19. Respiratory System I I © The McGraw-Hill

Human Anatomy and Excretion Companies, 2001

Physiology, Ninth Edition

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