Control of Ventilation Flashcards
What is eupnoea?
Normal breathing
What is apneusis?
Deep gasping inspiration and holding breath in then quick release
What does the pneumotaxic centre in the pons do?
Inhibits inspiratory phase
What does the apneustic centre in the pons do?
Prolongs inspiration
What are the 4 main respiratory nuclei in the medulla?
- Dorsal respiratory group (in nucleus tractus solitarius)
- Ventral respiratory group
- Pre-Botzinger complex
- Botzinger complex
Which respiratory nucleus is thought to be the key centre of respiratory rhythmogenesis?
pre-Botzinger complex
What kind of neurones does the dorsal respiratory group contain?
Inspiratory neurons
What kind of neurones does the ventral respiratory group contain?
Expiratory neurons
Where are the stretch receptors that affect breathing located?
Smooth muscle of the bronchial walls
What do the stretch receptors do to affect respiration?
Make inspiration shorter
Delay next respiratory cycle
(Negative feedback)
What is the name of the reflex where inflation of the lungs inhibits inspiration?
Hering-Breuer inflation reflex
Not in play in normal breathing but important in babies
What is the name of the reflex where deflation augments inspiration?
Deflation reflex
What do the juxtapulmonary receptors do?
In alveolar/bronchial walls, close to capillaries
Often activated in response to irritants or pulmonary embolism/oedema
Cause apnoea/rapid shallow breathing - cause breathlessness
What do the irritant receptors do?
Throughout airways between epithelial cells
Protective reflex - stops other irritants getting down
Which receptors are responsible for the deep breaths seen every 5-20 mins at rest preventing slow collapse of lungs during quiet breathing?
Irritant receptors
What do proprioceptive afferents do in the respiratory system?
Muscle spindles/Golgi tendon organs stimulated by change in length of muscles
Important for dealing with increased load and optimising tidal volume/frequency
How does pain receptor stimulation affect breathing?
Causes brief apnoea followed by increased breathing
Describe the ventilatory response to CO2 graph?
Linear relationship between alveolar PCO2 and ventilation up to a point then depression of respiratory centre - acidosis interferes with neural function (breathe less)
This depression also occurs in severe hypoxia
What happens at very low levels of CO2 on the ventilation graph?
Ventilation levels off
Never stop breathing all together
What is the relationship between PACO2 and alveolar ventilation ?
Inverse proportion
Halving ventilation rate doubles PACO2
What happens to the CO2 ventilation graph in metabolic alkalosis?
It shifts to the right (parallel straight line)
What happens to the CO2 ventilation graph in metabolic acidosis?
It shifts to the left (parallel straight line)
What does the ventilation pO2 graph look like?
Non linear
Ventilation only really increases when O2 conc is less than 8kPa
What is the significance of the 8kPa on the O2 ventilation graph?
Same pressure that Hb has reduced affinity for O2 - O2 comes off Hb at that pressure - breathe more at this point
How does hypercapnia change the O2 ventilation graph?
Shifts it up - higher ventilation rate for any conc of O2
Synergistic - combined effect greater than individual effects
What are the 2 types of chemoreceptors?
Central
Peripheral
What determines the interstitial pH (around the chemoreceptors)?
Diffusion of CO2 from the blood
Diffusion of HCO3- from CSF
What do the central chemoreceptors respond to?
pH of CSF
What is the [H+] proportional to at the central chemoreceptor?
pco2/ [HCO3-]
How much of response to raised pCo2 are central chemoreceptors responsible for?
80%
How quick is the response of central chemoreceptors?
Slow - 20 s
What occurs during prolonged hypercapnia?
CSF pH returns to normal
Ventilatory drive decreases
E.g. in COPD patients
What occurs at altitude to CSF composition?
CSF intially alkaline (breathe off lots of CO2 because of increased hypoxic drive)
CSF returns to normal and drive increases
What are people at altitude at risk of?
Hypobaric hypoxia
What are the 2 types of peripheral chemoreceptor?
Aortic bodies
Carotid bodies
What are the aortic bodies innervated by?
Vagus nerve
What are the carotid bodies innervated by?
Carotid sinus nerve
What are the two types of cells found in peripheral chemoreceptors?
Type 1 (glomus cells) Type 2 (sheath cells)
What do type 1 (glomus cells) do?
Rich in neurotransmitters
Contact axons
What do type 2 (sheath cells) do?
Enclose type 1 cells
How quick is the response of peripheral chemoreceptors?
Very fast - respond breath by breath
What do central chemoreceptors respond to?
Arterial pCO2
Give examples of loss of CO2 drive
Chronic hypercapnia
Adaptation
Don’t give them oxygen for prolonged time - taking away respiratory drive
What is Cheyne-Stokes respiration?
Rapid breathing then pauses
Sats oscillate
Heart failure/stroke/altitude sickness
What is central sleep apnoea?
Breathing stops during sleep
Do a sleep study
What is obstructive sleep apnoea?
Lose muscle tone in neck
Fat around neck obstructs airway
Aroused and oxygen sats returns to normal when awoken
