Apneusis is a condition characterised by noticeable, persistent end-inspiratory pauses that can be induced in vagotomized animals via pontine transection. While the phenomenon of apneusis is well understood, anatomical definitions for a neuronal aggregate that can be fairly referred to as the apneustic centre are missing. Apneusis is operationally defined as a lack of regular inspiratory off-switching to activate. Apneusis can be caused by a variety of lesions or pharmaceutical interventions. Apneusis is induced systemically, but not locally, by antagonists of the glutamate receptor’s N-methyl-d-aspartate (NMDA) subtype, but not by non-NMDA antagonists, defining the neurotransmitter system involved and the absence of a specific inducing site. However, NMDA antagonists cause altered membrane potentials in ventral respiratory neurons.
In humans, apneustic respiration is uncommon. Children with hypoxic-ischemic brain injury or other brainstem lesions may have apneustic breathing with cyanosis during inspiratory pauses. Tandospirone or buspirone, both of which are serotonin-1A agonists, restore respiratory function. Five patients with cervicomedullary compression due to achondroplasia had “significantly reduced” apneustic breathing patterns following decompressive surgery. This clinical description is notable for the absence of a compressive impact at the level of the pneumotaxic centre and the integrity of the vagus nerves.
Respiratory Causes
The respiratory centre is divided into three primary groups, two of which are located in the medulla and one of which is located in the pons. The dorsal respiratory group and the ventral respiratory group are the two respiratory groups found in the medulla. It is composed of two sections of the pontine respiratory group, which are the pneumotaxic centre and the apneustic centre. The pontine respiratory group is located in the pons. The medullary groups in the dorsal and ventral thoracic regions regulate the basic rhythm of respiration. They are divided into two groups, with one group on either side of the brainstem.
Dorsal respiratory group
The dorsal respiratory group (DRG) plays a critical role in respiration control, beginning inspiration (inhalation). The DRG is a mass of neurons that spans the majority of the length of the dorsal medulla. They are located near the spinal cord’s central canal, immediately behind the ventral group. They establish and sustain the respiratory rate.
The majority of neurons are concentrated in the solitary tract’s nucleus. Other significant neurons are located in nearby locations, including the medulla’s reticular material. The solitary nucleus receives sensory input from the pontine respiratory group and two cranial nerves — the vagus and glossopharyngeal nerves. The solitary nucleus receives signals from peripheral chemoreceptors, baroreceptors, and various types of receptors in the lungs, most notably stretch receptors. Thus, the dorsal respiratory group is viewed as an integrating centre that provides output to the ventral respiratory group, which modifies the respiratory rhythm.
Ventral respiratory group
A collection of neurons in the medulla known as the ventral respiratory group (VRG) controls the exhalation (expiratory) area of respiratory regulation. The VRG is made up of four groups of neurons that are located in the ventral respiratory group (VRG). A small portion of the medulla in the ventrolateral part of the brain, approximately 5 mm anterior and lateral to the dorsal respiratory group, is home to this group. Neurons in the nucleus ambiguus, the nucleus retroambiguus, and the interneurons of the pre-Bötzinger complex are among those that are implicated in this process.
The VRG is made up of neurons that are both inspiratory and expiratory in nature. The ventral respiratory group of neurons is active during strong breathing and dormant during quiet, restful respirations, according to the findings. The VRG communicates with the apneustic centre by sending inhibitory impulses.
Pontine respiratory group
The pontine respiratory group (PRG) comprises the pneumotaxic and apneustic centres located in the pontine tegmentum of the pons. These are connected to one another and to the single nucleus.
Pneumotaxic centre
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Pneumotaxic centres are positioned in the pons’ upper portion. The sub parabrachial nucleus and the medial parabrachial nucleus are its nuclei. Both the rate and pattern of breathing are regulated by the pneumotaxic centre.
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The pneumotaxic centre is thought to act as an antagonist to the apneustic centre (which results in irregular breathing during inhalation), blocking inhaling cyclically. The pneumotaxic centre is in charge of limiting inspiration and acting as an inspiratory shut-off switch (IOS).
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It successfully decreases the tidal volume and regulates the respiratory rate by limiting the burst of action potentials in the phrenic nerve. Without the centre, the depth of respiration increases and the respiratory rate decreases.
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The pneumotaxic centre controls the amount of air that can be inhaled with each breath. The dorsal respiratory group exhibits constant duration and interval rhythmic bursts of activity.
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When a faster rate of breathing is required, the pneumotaxic centre signals the dorsal respiratory group to increase its pace of breathing. When deeper breaths are required, activity spurts are prolonged. The pneumotaxic centre is where the body stores all of the information necessary for respiration. If this is damaged or harmed in any way, breathing becomes nearly impossible.
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One study examined paralysed anaesthetized cats before and after bilateral vagotomy. The ventilation of awake and anaesthetized cats breathing either air or CO2 was monitored.
Apneustic centre
The apneustic centre in the lower pons appears to promote inhaling by continuously stimulating neurons in the medulla oblongata. The apneustic centre communicates with the dorsal group in the medulla to postpone the switch off,’ the inspiratory off switch (IOS) signal from the pneumotaxic centre’s inspiratory ramp. It regulates the rate of breathing by sending positive impulses to the neurons responsible for inhalation. The pulmonary stretch receptors, as well as the pneumotaxic centre, block the apneustic centre. Additionally, it sends an inhibiting impulse to the pneumotaxic centre.
Causes of Apneustic centre
It is caused by strokes or trauma to the pons or higher medulla. This pattern of breathing is caused by the simultaneous loss of input from the vagus nerve and the pneumotaxic centre. It is a concerning symptom, with an unfavourable prognosis in general.
Additionally, certain substances, such as ketamine, might produce it momentarily. It results in craniocerebral damage.