Neural Control of Breathing Flashcards
How is breathing initiated? What causes respiratory muscles to contract?
- Breathing is initiated by the neural activation of respiratory muscles, which provides the movement required for ventilation.
- As respiratory muscles consist of skeletal muscle, they require neural inputs / stimulations to contract.
- Innervation from motor neurons synapsing from descending spinal tracts provide the contractile signal.
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What effect does spinal chord injury, motor neuron disease, muscular dystrophy have on breathing?
- It can cause the person to be unable to breathe as the nerve impulses are not recieved by the respiratory muscles.
- So there is no muscle contration leading to failure in ability to breathe.
Muscular dystrophy (MD) meaning - It is a group of muscle diseases that results in increasing weakening and breakdown of skeletal muscles over time.
Which muscles (including accessory muscles) are utilised in quiet/ forced inspiration and expiration?
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How is the basic breathing pattern generated by neuronal systems in the brainstem?
- The breathing pattern is initiated in the brainstem.
- Here you have an extremely complex series of different neural networks that function together to take various signals from different parts of the body and decide the breathing pattern.
- The breathing rate, depth of breath to meet the metabolic demands of the body, and related factors are decided here and signals are accordingly sent to different respiratory muscles in a rhythmeic pattern in order to breathe.
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How does the central pattern generator (CPG) determine how often and hard to breathe?
- Signals from various inputs provide feedback, which integrate to regulate breathing.
- Examples of such signals would be: -
- What is the pH in the CSF (cerebrospinal fluid)? (typically determined by PaCO2)
- How much H+, CO2 and O2 is in arterial blood?
- What is the current lung volume? How stretched are the lungs?
- Is there stimualtion from higher emotion centres or ANS?
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List the two main chemoreceptors, where they are located, and what changes they detect in the body.
- The two main chemoreceptors involved in respiratory feedback are: -
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CENTRAL CHEMORECEPTORS: -
- These are located on the ventrolateral surface of the medulla oblongata, and indirectly monitor changes in arterial CO2.
- Although central respiratory chemo-receptors (CRC) respond to changes in [H+] within cerebrospinal fluid, as H+ does not cross the blood brain barrier (as it is charged), CRC do not directly respond to changes in blood pH (except via CO2).
- They can be desensitised over time from chronic hypoxia (oxygen deficiency) and increased carbon dioxide.
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PERIPHERAL CHEMORECEPTORS: -
- These are located in the aortic body, which detect changes in blood oxygen and carbon dioxide, but not pH, and in the carotid body, which detects all three.
- They are activated by low PaO2 and high PaCO2 and acidaemia.
- They signal to respiratory centres in medulla (via sensory nerves) to increase ventilation (negative feedback).
- They do not desensitise, and have less of an impact on the respiratory rate compared to the central chemoreceptors.
- The two chemoreceptors then send the signals to the respiratory pattern generator and alter the rate of ventilation.
Ventrolateral meaning - situated towards the junction of the ventral and lateral sides.
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What is the hypercapnic drive?
- Ventilation is generally proportional to the PaCO2.
- When the PaCO2 increases you feel the urge to breathe.
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What is the hypoxic drive?
- The hypoxic drive is a form of respiratory drive in which the body uses oxygen chemoreceptors instead of carbon dioxide receptors to regulate the respiratory cycle.
- So respiration is only undertaken when there is a decrease in PaO2.
- The situation where the hypoxic drive start to take on a greater importance than the hypercapnic drive would be where a patient is suffereing from high levels of CO2 due to COPD.
- Since there people have a high level of CO2 on a chronic basis due to insufficient ventilation they start to become tolerant to high levels of CO2.
- This is when hypoxic drive begins to take on a bigger role compared to hypercapnic drive.
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What is central sleep apnoea, and what are some of its causes?
- Central sleep apnoea is the temporary cessation of breathing during sleep caused by dysfunction of the processes that initiates breathing.
- Potential negative effects on health include tiredness, cardiovascular complications, and metabolic dysfunction.
- Causes:
- Stroke – damage to respiratory centres in brain.
- Drugs (e.g. opioids) – suppression of neuronal activity.
- Altitude – e.g. Cheyne - Stokes respiration.
- Central hypoventilation syndrome – injury/trauma to brainstem, or congenital (‘Ondine’s curse’).
What is obstructive sleep apnoea, and what are some risk factors?
- Obstructive sleep apnoea is the blockade of the upper respiratory tract during sleep.
- The relaxation of the genioglossus muscle (the main muscle in the tonuge) can obstruct the upper airway.
- Some risk factors include: -
- Obesity.
- Alcohol/ sedatives.
- Smoking
How do we investigate someones sleeping pattern?
- We can investigate someone’s sleeping pattern using a polysomnography.
- Polysomnography records your brain waves, the oxygen level in your blood, heart rate and breathing, as well as eye and leg movements during the study.
Describe what will come of a situation of hypocapnia before jumping into shallow waters.
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HYPERVENTILATION:
- Overbreathing, either consciously or as a results of overexertion, artificially lowers carbon dioxide levels (hypocapnia).
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OXYGEN DROPS:
- As the breath hold begins, oxygen is metabolised and carbon dioxide levels increase.
- As the breath hold continues, the body becomes starved of oxygen.
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UNCONCIOUSNESS:
- Under normal circumstances, increased carbon dioxide would trigger a breath, but because the CO2 levels were so low upon submersion (due to hyperventilation), there is not enough to initiate a breath, and the swimmer loses conciousness.
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DROWNING:
- Once the swimmer loses conciousness, the body reacts and forces a breath.
- That causes the lungs to fill with water and, without an immediae rescue, a drowning death is all but certain.
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Describe Cheyne-Stokes respiration.
- Cheyne-Stokes respiration is oscillating apnoea and hyperpnoea (Hyperpnoea is increased depth and rate of breathing).
- Cheyne–Stokes respiration is an abnormal pattern of breathing characterized by progressively deeper, and sometimes faster, breathing followed by a gradual decrease that results in a temporary stop in breathing called an apnea. The pattern repeats, with each cycle usually taking 30 seconds to 2 minutes
- First, there is a pathological stimulus (such as increased altitude, CR disfunction, heart failure, etc.) that results in hypercapnia and hypoxaemia.
- To compensate, the body starts hypervnetilating.
- This causes hypocapnia, and thus alkalosis.
- This causes the body to decrease its respiratory drive, and the body will compensate with hypoventilation.
- This causes hypercapnia and hypoxaemia, and the cycle continues.