39.10: Breathing - Types of Breathing

Types of breathing in humans include eupnea, hyperpnea, diaphragmatic, and costal breathing; each requires slightly different processes.

Learning Objectives

• Differentiate among the types of breathing in humans, amphibians, and birds

Key Points

• Eupnea is normal quiet breathing that requires contraction of the diaphragm and external intercostal muscles.
• Diaphragmatic breathing requires contraction of the diaphragm and is also called deep breathing.
• Costal breathing requires contraction of the intercostal muscles and is also called shallow breathing.
• Hyperpnea is forced breathing and requires muscle contractions during both inspiration and expiration such as contraction of the diaphragm, intercostal muscles, and accessory muscles.
• Amphibians utilize gills for breathing early in life and later develop primitive lungs in their adult life; additionally, they are able to breathe through their skin.
• Birds have evolved a directional respiratory system that allows them to obtain oxygen at high altitudes: air flows in one direction while blood flows in another, allowing efficient gas exchange.

Key Terms

• eupnea: normal, relaxed breathing; healthy condition of inhalation and exhalation
• hyperpnea: deep and rapid respiration that occurs normally after exercise or abnormally with fever or various disorders
• intercostal: between the ribs of an animal or person

Types of Breathing

There are different types, or modes, of breathing that require a slightly different process to allow inspiration and expiration. All mammals have lungs that are the main organs for breathing. Lung capacity has evolved to support the animal’s activities. During inhalation, the lungs expand with air and oxygen diffuses across the lung’s surface, entering the bloodstream. During exhalation, the lungs expel air and lung volume decreases. The various types of breathing, specifically in humans, include:

1) Eupnea: a mode of breathing that occurs at rest and does not require the cognitive thought of the individual. During eupnea, also referred to as quiet breathing, the diaphragm and external intercostals must contract.

2) Diaphragmatic breathing: a mode of breathing that requires the diaphragm to contract. As the diaphragm relaxes, air passively leaves the lungs. This type of breathing is also known as deep breathing.

Figure \(\PageIndex{1}\): Diaphragmatic breathing: Animation of a diaphragm exhaling and inhaling, demonstrating diaphragmatic breathing. During inhalation, the diaphragm is contracted which increases the volume of the lung cavity. During exhalation, the diaphragm is relaxed which decreases the volume of the lung cavity.

3) Costal breathing: a mode of breathing that requires contraction of the intercostal muscles. As the intercostal muscles relax, air passively leaves the lungs. This type of breathing is also known as shallow breathing.

4) Hyperpnea: a mode of breathing that can occur during exercise or actions that require the active manipulation of breathing, such as singing. During hyperpnea, also known as forced breathing, inspiration and expiration both occur due to muscle contractions. In addition to the contraction of the diaphragm and intercostal muscles, other accessory muscles must also contract. During forced inspiration, muscles of the neck, including the scalenes, contract and lift the thoracic wall, increasing lung volume. During forced expiration, accessory muscles of the abdomen, including the obliques, contract, forcing abdominal organs upward against the diaphragm. This helps to push the diaphragm further into the thorax, pushing more air out. In addition, accessory muscles (primarily the internal intercostals) help to compress the rib cage, which also reduces the volume of the thoracic cavity.

Types of Breathing in Amphibians and Birds

In animals such as amphibians, there have been multiple ways of breathing that have evolved. In young amphibians, such as tadpoles that do not leave the water, gills are used to breathe. There are some amphibians that retain gills for life. As the tadpole grows, the gills disappear and lungs grow. These lungs are primitive and not as evolved as mammalian lungs. Adult amphibians are lacking or have a reduced diaphragm, so breathing via lungs is forced. The other means of breathing for amphibians is diffusion across the skin. To aid this diffusion, amphibian skin must remain moist.

Other animals, such as birds, must face a unique challenge with respect to breathing, which is that they fly. Flying consumes a large amount of energy; therefore, birds require a lot of oxygen to aid their metabolic processes. They have evolved a respiratory system that supplies them with the oxygen needed to enable flying. Similar to mammals, birds have lungs, which are organs specialized for gas exchange. Oxygenated air, taken in during inhalation, diffuses across the surface of the lungs into the bloodstream, while carbon dioxide diffuses from the blood into the lungs and is expelled during exhalation. However, the details of breathing between birds and mammals differ substantially.

In addition to lungs, birds have air sacs inside their body that are attached to the lungs. Air flows in one direction from the posterior air sacs to the lungs and out of the anterior air sacs. The flow of air is in the opposite direction from blood flow, which allows efficient gas exchange. This type of breathing enables birds to obtain the requisite oxygen, even at higher altitudes where the oxygen concentration is low. This directionality of airflow requires two cycles of air intake and exhalation to completely remove the air from the lungs.

Figure \(\PageIndex{1}\): Avian respiratory system: (a) Birds have a flow-through respiratory system in which air flows unidirectionally from the posterior sacs into the lungs, then into the anterior air sacs. The air sacs connect to openings in hollow bones. (b) Dinosaurs, from which birds descended, have similar hollow bones and are believed to have had a similar respiratory system.