What is Hering-breuer reflex? - Definition, Mechanism, Importance

The Hering-Breuer reflex is a reflex that prevents the lungs from becoming overinflated. Excessive lung stretching during deep breaths triggers a response from pulmonary stretch receptors found in the smooth muscle of the airways. Once they have been activated, they block the activity of the inspiratory neurons that are located in the apneustic area of the pons by sending action potentials through the long myelinated fibers of the paired vagus nerves. Consequently, inspiration is impeded, resulting in expiration.

Adults exhibited a diminished ability to show the Hering-Breuer reflex, but premature babies and neonates exhibit a considerably stronger representation. In addition, there is evidence that the hering-breuer reflex plays a role in regulating lung volume at a young age, suggesting that it may play a crucial role. In fact, abnormal functioning of these vagal circuits may contribute to numerous infant respiratory disorders.

Definition

The Hering-Breuer reflex is defined as a regulatory reflex that activates to prevent the lungs from becoming overinflated. When there is an excessive amount of stretching of the lung caused by heavy inspirations, pulmonary stretch receptors that are located in the smooth muscle of the airways become activated.

Mechanism

The Hering-Breuer reflex is controlled by a neuronal circuit that combines multiple areas of the central nervous system, as well as motor and sensory parts of the vagus nerve. A rise in the sensory activity of the vagus nerve leads to an upsurge in the activity of the nucleus of the solitary tract, which in turn delivers inhibitory input to the nucleus ambiguus. The nucleus ambiguus regulates the rate of the heart by sending motor fibers to the heart through the vagus nerve. Heart rate is ultimately raised by enhanced pulmonary stretch receptor activation, which results in nucleus ambiguus inhibition. As a result, a rise in heart rate is quite natural during inspiration.

Importance

According to scientists, the reflex significantly influences how quickly and deeply we breathe. In neonates and adult people whose tidal volume is greater than 1 L, such as during exercise, the reflex may determine breathing rate and depth. The lack of this reflex aids in diagnosing brain death.

It is a crucial mechanism for the control and protection of the respiratory system in animals, making volume-dependent regulation possible. Interestingly, it was previously thought that adult human breathing at eupneic tidal volumes was unaffected by this reflex. However, more recent research has shown that it is possible to identify this reflex in adults, and it can be done readily after chest wall movement has ceased. The volume required to activate the HBR is more than physiologic tidal volumes, hence it is generally regarded as undetectable despite the fact that this reflex is present and (in some circumstances) identifiable in adult humans.