Lecture 5: Resp control Flashcards
What efferent nerves are required for inspiratory muscles?
Diaphragm(s): phrenic nerves, C3-C5
External intercostal muscles: thoracic nerves T1-T11
Accessory muscles: sternocleidomastoid (XI cranial nerve) and scalene muscles (C3-C8)
What efferent nerves are required for expiratory muscles?
Abdominal wall: T5-T12
External intercostal muscles: T1-T12
What is the role of the pons?
Not essential for respiration but exerts fine control over medullary neurons
What are the dorsal respiratory group of neurons required for?
Trigger inspiratory impulses
What are the ventral respiratory group of neurons required for?
Trigger inspiratory and expiratory impulses (during exercise or other times of active exhalation)
What is the role of the rhythm generator in the medulla?
Controls the basic, automatic pattern of breathing - the pacemaker for breathing is not a single cell but a group of neurons concentrate in the Pre-Botzinger complex
Where are the group of neutrons that act as the pacemaker for breathing?
In the Pre-Botzinger complex
What afferent inputs may impact breathing rate?
- Emotional inputs from the cerebral cortex
- Lung mechanoreceptors
- Chemoreceptors (central and peripheral)
What is the role of lung stretch receptors(vagal nerve afferent fibres)?
Sense lung stretch during breathing to terminate breath to prevent over-stretching
Sense abnormal changes in airway mechanical properties
What is the role of irritant and particulate receptors (vagal nerve afferent fibres)?
C-fibre neurons: activated by oedema and molecules such as bradykinin
Irritant receptors (sometimes called ‘cough receptors’): respond to punctate mechanical stimuli
What is detected by the central chemosensors?
[H+] in the CSF
[H+] in the CSF reflects blood [H+], PaCO2 and CSF CO2 but these are NOT directly sensed by central chemoreceptors
What area of the brain responds to input from central chemoreceptors?
Hindbrain
Where are the peripheral chemosensors?
Carotid body: bundle of cells outside the bifurcation of carotid arteries
Aortic body: bundle of cells within aortic arch
Carotid and aortic bodies are back up for each other, but normally the carotid bodies do bulk of peripheral sensing
Both respond to PO2 (hypoxaemia) and CO2. Carotid bodies also detect pH.
What is detected by carotid body?
PO2, CO2 and pH
What is detected by the aortic body?
PO2 and CO2
What is the relationship between sensitivity to PO2 and PCO2?
Sensitivity to PO2 is altered by PCO2: more sensitive to hypoxaemia in setting of hypercarbia
Give an example of a volatile acid?
CO2
What is respiratory acidosis?
The build up (retention) of CO2
What are fixed acids?
Non-volatile acids have to be physically eliminated from the body, typically via the kidneys
They are products from the oxidation of dietary substrates. Baseline production is well managed by the kidneys and liver, where lactate is converted to glucose in the liver
Increased production of acids, especially lactic acid, can outstrip normal clearance
How do the kidneys eliminate fixed acids?
Filtration and elimination of the conjugate base of acids: urate, lactate, and ketones are main types
What are the 6 steps to ABG interpretation?
Step 1: Examine the pH, PCO2 and HCO3 –
Step 2: Determine the primary process. Does the patient have an acidaemia or alkalaemia based on the pH? If so, what type is it?
Step 3: If a metabolic acidosis is present, calculate the anion gap
Step 4: Identify the compensatory process
Step 5: Determine if a mixed acid-base disorder is present
Step 6: Determine the cause
What pH is suggestive of acidaemia?
A low blood pH (< 7.38)
What pH is suggestive of alkalaemia?
A high blood pH (> 7.42)
How do you determine respiratory acidosis?
High PCO2 (> 44 mmHg / 5.9 kPa)
