Flashcards in S2: Neural Control of Breathing Deck (22):
What is breathing?
Breathing is a rhythmic process that maintains O2 and CO2 pressure gradients between alveoli and blood.
List some factors that increase O2 demand and CO2 production
- Excersize (increase activity increases ATP production and increases VO2 - volume of O2 consumed)
- Metabolic Dysfunction
What does alveolar ventilation depend on?
Alveolar ventilation depends on the volume of fresh air inhaled each breath and the rate of breathing
VA = (VT - VD) x f
Explain neural control of breathing
Breathing is produced by neural activation of respiratory muscles.
- Respiratory muscles provide the movement required for ventilation. As respiratory muscles consist of skeletal muscle, they require neural input/stimulation to contract.
- Innervation from motor neurones synapsing from descending spinal tracts provide contractile signal
Muscles utilised in inspiration
Quiet breathing: Diaphragm
Respiratory: External intercostals
Accessory: Pectorals, Sternomastoid, Scalene
Muscles utilised in expiration
What is the respiratory pattern generator/central pattern generator?
The basic breathing pattern is generated by neuronal systems within the brainstem.
The brain receives inputs from various sources and integrates this to determine our breathing by generating output to the lungs.
Dorsal respiratory group (inspiratory neurones - initiates inspiration unconsciously)
Ventral (all inspiration and expiration)
What do central chemoreceptors respond to?
Central chemoreceptors respond indirectly to changes in arterial PCO2
Where are central respiratory chemoreceptors (CRC) found?
Central respiratory chemoreceptors (CRC) present in the medulla
How do central chemoreceptors indirectly measure changes in arterial pCO2?
Although CRC respond to changes in [H+] within the cerebrospinal fluid as H+ doesn't cross the blood brain barrier.
CRC do not directly respond to changes in blood pH except via CO2.
H+ stimulates central chemoreceptors which takes information to the respiratory control centres that increase or decrease ventilation.
What is the main stimulus of breathing?
What do peripheral chemoreceptors respond to?
Peripheral chemoreceptors respond to changes in arterial O2, CO2 and PH.
They are activated by decreased PaO2, increased PaCO2 and acidaemia.
What do peripheral chemoreceptors do?
They respond to changes in arterial O2, CO2 and pH.
They then signal to respiratory centres in the medulla (via sensory nerves) to increase ventilation (negative feedback)
What is hypercapnic drive?
This is where the body uses carbon dioxide chemoreceptors to regulate the respiratory cycle
Ventilation is generally proportional to PaCO2 so the higher the levels of CO2, the more ventilation occurs.
What is 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
Hypoxic drive only kicks in during hypoxaemia (low PaO2) stimulates increased ventilation
Describe the stages of shallow water blackout
Overbreathing (consciously or due to overexertion) artificially lowes CO2 levels
In the water breath is held. Oxygen is metabolised and CO2 levels increase. Body gradually becomes starved of oxygen.
Under normal circumstances, increased CO2 would trigger a breath but because CO2 levels were low upon submertion, CO2 levels are not high enough to trigger a breath and swimmer loses consciousness.
Once the swimmer loses consciousness, the body reacts and forces a breath. This causes the lungs to fill with water which can cause drowning if individual is not rescued.
What can be used to investigate sleep apnoea?
What is sleep apnoea?
Temporary cessation of breathing during sleep
Effect of sleep apnoea on health
- Tiredness (poor sleep quality)
- Cardiovascular complications (stress and increased SNS tone)
-Obesity/Diabetes (inflammation and metabolic dysfunction)
What is obstructive sleep apnoea?
Name some risk factors
Obstructive sleep apnoea: Blockade of upper respiratory tract during sleep e.g. by tongue
What is central sleep apnoea?
Name some causes
Central sleep apnoea is dysfunction in the process that initiates breathing
- Stroke which damages respiratory centres in the brain
- Drugs e.g. opiods that suppress neuronal activity
- Central hypoventilation syndrome - injury/trauma to brainstem, or congenital ('ondines curse')
- Neonates - Continuing development of respiratory centres
- Altitude e.g. cheyne stokes respiration