The Hering–Breuer inflation reflex, named for

Josef Breuer Josef Breuer ( ; ; 15 January 1842 – 20 June 1925) was an Austrian physician who made discoveries in neurophysiology, and whose work during the 1880s with his patient Bertha Pappenheim, known as Anna O., led to the development of the "cathart ...

and

Ewald Hering Karl Ewald Konstantin Hering (5 August 1834 – 26 January 1918) was a German physiologist who did much research in color vision, binocular perception, eye movements, and hyperacuity. He proposed opponent color theory in 1892. Born in Gersd ...

, is a

reflex In biology, a reflex, or reflex action, is an involuntary, unplanned sequence or action and nearly instantaneous response to a stimulus. Reflexes are found with varying levels of complexity in organisms with a nervous system. A reflex occurs ...

triggered to prevent the over-inflation of the

lung The lungs are the primary Organ (biology), organs of the respiratory system in many animals, including humans. In mammals and most other tetrapods, two lungs are located near the Vertebral column, backbone on either side of the heart. Their ...

Pulmonary stretch receptors Pulmonary stretch receptors are mechanoreceptors found in the lungs. When the lung expands, the receptors initiate the Hering-Breuer reflex, which reduces the respiratory rate. This signal is transmitted by vagus nerve. Increased firing from th ...

present on the wall of bronchi and bronchioles of the airways respond to excessive stretching of the lung during large inspirations. Once activated, they send

action potential An action potential (also known as a nerve impulse or "spike" when in a neuron) is a series of quick changes in voltage across a cell membrane. An action potential occurs when the membrane potential of a specific Cell (biology), cell rapidly ri ...

s through large

myelin Myelin Sheath ( ) is a lipid-rich material that in most vertebrates surrounds the axons of neurons to insulate them and increase the rate at which electrical impulses (called action potentials) pass along the axon. The myelinated axon can be lik ...

ated fibers of the

vagus nerve The vagus nerve, also known as the tenth cranial nerve (CN X), plays a crucial role in the autonomic nervous system, which is responsible for regulating involuntary functions within the human body. This nerve carries both sensory and motor fibe ...

to the inspiratory area in the medulla and apneustic center of the

pons The pons (from Latin , "bridge") is part of the brainstem that in humans and other mammals, lies inferior to the midbrain, superior to the medulla oblongata and anterior to the cerebellum. The pons is also called the pons Varolii ("bridge of ...

. In response, the inspiratory area is inhibited directly and the apneustic center is inhibited from activating the inspiratory area. This inhibits inspiration, allowing expiration to occur. The Hering–Breuer inflation reflex should not be confused with the deflation reflex discovered by the same individuals, Hering and Breuer. The majority of this page discusses the ''inflation'' reflex; the deflation reflex is considered separately at the end.

History

Josef Breuer and Ewald Hering reported in 1868 that a maintained distention of the lungs of anesthetized animals decreased the frequency of the inspiratory effort or caused a transient apnea. The stimulus was therefore pulmonary inflation.

Anatomy and physiology

The Hering-Breuer reflex, put simply, is what keeps the lungs from over-inflating with inspired air. The neural circuit that controls the Hering–Breuer inflation reflex involves several regions of the

central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain, spinal cord and retina. The CNS is so named because the brain integrates the received information and coordinates and influences the activity o ...

, and both sensory and motor components of the

. Increased sensory activity of the pulmonary-stretch lung afferents (via the vagus nerve) results in inhibition of the central inspiratory drive and thus inhibition of inspiration and initiation of expiration. The lung afferents also send inhibitory projections to the cardiac vagal motor neurones (CVM) in the nucleus ambiguus (NA) and dorsal motor vagal nucleus (DMVN). The CVMs, which send motor fibers to the

heart The heart is a muscular Organ (biology), organ found in humans and other animals. This organ pumps blood through the blood vessels. The heart and blood vessels together make the circulatory system. The pumped blood carries oxygen and nutrie ...

via the vagus nerve, are responsible for tonic inhibitory control of

heart rate Heart rate is the frequency of the cardiac cycle, heartbeat measured by the number of contractions of the heart per minute (''beats per minute'', or bpm). The heart rate varies according to the body's Human body, physical needs, including the nee ...

. Thus, an increase in pulmonary stretch receptor activity leads to inhibition of the CVMs and an elevation of heart rate (

tachycardia Tachycardia, also called tachyarrhythmia, is a heart rate that exceeds the normal resting rate. In general, a resting heart rate over 100 beats per minute is accepted as tachycardia in adults. Heart rates above the resting rate may be normal ...

). This is a normal occurrence in healthy individuals and is known as

sinus arrhythmia Sinus arrhythmia is a commonly encountered variation of ''normal'' sinus rhythm. Sinus arrhythmia characteristically presents with an irregular rate in which the variation in the R-R interval is more than 0.12 seconds (120 milliseconds). Additional ...

Rate and depth of breathing

Early physiologists believed the reflex plays a major role in establishing the rate and depth of breathing in humans. While this may be true for most animals, it is not the case for most adult humans at rest. However, the reflex may determine breathing rate and depth in newborns and in adult humans when

tidal volume Tidal is the adjectival form of tide. Tidal may also refer to: * ''Tidal'' (album), a 1996 album by Fiona Apple * Tidal (king), a king involved in the Battle of the Vale of Siddim * TidalCycles TidalCycles (also known as Tidal) is a live coding ...

is more than 1 L, as when exercising.

Hering–Breuer deflation reflex

The Hering–Breuer deflation reflex serves to shorten exhalation when the lung is deflated. It is initiated either by stimulation of stretch receptors or stimulation of proprioceptors activated by lung deflation. Like the inflation reflex, impulses from these receptors travel afferently via the vagus. Unlike the inflation reflex, the afferents terminate on inspiratory centers rather than the pontine apneustic center. These reflexes appear to play a more minor role in humans than in non-human mammals.

Clinical use

The absence of this reflex contributes to the diagnosis of brain death.

History

Anatomy and physiology

Rate and depth of breathing

Hering–Breuer deflation reflex

Clinical use

References

Further reading