Control of Ventilation Flashcards
Definition of apneusis
Prolonged inspiration, holding breath
Definition of apnoea
No breathing, no change in phasic respiration
Definition of eupnoae
Normal pattern of breathing
Definition of pulmonary congestions
Occurs in heart failure, decreased CO => back up of fluid in venous circulation
P here increases => fluid goes into alveoli
Describe the 2 methods of neural control in the pons and their functions
- pneumotaxic center
- apneustic center
Pneumotaxic center
- inhibit inspiration
- without it => apneusis
Apneustic center
- prolongs inspiration
- without it => gasping
Describe the 2 methods of neural control in the medulla and their functions
-what nuclei make up each group?
- dorsal resp group
- afferents and efferents
- ventral resp group
- efferents
Dorsal resp group
-NST => phrenic, intercostals
- inspiratory neurones only, fire before, during respiration => controls depth, rate, basal rhythm
- inhibits expiratory neurones in ventral/pons group
Ventral resp group
-NA, NRA, BC, PBC (key to resp rhythmogenesis) => phrenic, intercostals
- inspiratory and expiratory neurones
- active only in forced inspiration and expiration
- expiratory neurones inhibit inspiratory neurones
Name the 7 afferents that affect ventilation rate
- stretch receptors
- juxtapulmonary receptors
- irritant receptors
- proprioceptive afferents
- pain receptors
- V
- arterial baroceptors
Describe the site, function, reflexes of the stretch receptors (medulla)
Bronchial SM
Makes inspiration shorter
Hering Breuer, inflation, inhibits inspiration
Deflation reflex, argument inspiration
Describe the site, function of the juxtapulmonary receptors (medulla)
What stimulates these receptors
Alveolar/bronchial walls near capillaries
Apnoea/rapid shallow breaths => decreased HR, BP
Laryngeal constriction
Skeletal muscle relaxation
React to dyspnoea Increased alveolar wall fluid Oedema Pulmonary congestion Microembolisms Inflammatory mediators
Describe the site, function of the irritant receptors (medulla)
What stimulates these receptors
Airway
Trachea => cough
Lower airway => hyperapnoea
Irritant gases, smoke, dust
Inflammation
Lung collapse under weight
Describe the site, function of the proprioceptive afferents to the medulla
Why are they important?
Resp muscles
Shortenings load of non resp muscles => increase BR
Increased load => increased tension => increased BR => increased TV
How do pain receptors affect the breathing rate
Result in brief apnoea => increased breathing
How does the trigeminal region affect breathing rate
Results in apnoea/spasm => decrease in HR, sneeze
How does the arterial baroreceptor affect the breathing rate
Stimulation decreases ventilation
Increased BP => decreased BR
What is the main principle of chemical control
How is CO2 prod, O2 consumption, H+ prod estimated
Ventilation must match metabolism
CO2 production estimated from PaCO2
O2 consumption estimated from PaO2
H+ production estimated from pH
Describe how the rate of ventilation changes with PaCO2
In the normal physiological range, as PaCO2 increases, ventilation rate increases
If PaCO2 exceeds normal physiological range => CO2 narcosis
If PaCO2 is below normal physiological range, there is always a basal level of ventilation
Describe how the rate of ventilation changes with changing pH and PaCO2
In the normal physiological range, as PaCO2 increases, ventilation rate increases
pH too low => hypoventilation/metabolic acidosis
PACO2 increases => vent increases
pH too high => hyperventilation/metabolic alkalosis
PACO2 increases => vent increases
Describe how the rate of ventilation changes with changing PaO2
- what happens if PaO2 is too low (<8kPa)
- what happens if PaO2 is too high
What is the relationship between hypoxia and hypercapnia
As PaO2 falls below 8kPa, rate of ventilation rapidly increases.
If too low => respiratory depression
If too high => respiratory depression
Synergistic relationship between hypoxia and hypercapnia => increase ventilation
Describe the central chemoreceptor
- location
- structure
- how does it function
- what is it affected by
Location
-IX, X exit in medulla
Structure
- HCO, H crosses CSF brain barrier
- CO2, O2 crosses BBB
- chemoreceptor surrounded by glial cell
Functions
- HCO buffer
- PCO2 => [H+] increases due to buffer, pH change detected by chemoreceptor
Properties
- only affected by PCO2
- 20s to respond
How do central chemoreceptors respond to altitude
Initially driven by hypoxic drive => alkali CSF
Vent drive decreases => restore pH => hypoxic drive continues
Cycles between the 2
How do central chemoreceptors respond to prolonged hypercapnia
- why is this bad
- what should we do to help
Hypercapnia => low pH => increase vent
Over time, chemoreceptor threshold decreases so vent drive falls
But still hypercapnia, hypoxic, must provide low flow O2 to continue the hypoxic drive
Describe the peripheral chemoreceptors
- location
- structure
- function
- properties
Location
- IX, carotid body => pons
- X, aortic bodies => pons
Structure
- T1 glomus cell surrounded by T2 sheath cell
- nerve fibres go to pons
Function
- Detect large changes in PO2
- increase vent rate in hypoxia
Properties
- only affected by PO2
- instant response
Describe the 2 types of sleep apnea
-how do they arise
- obstructive
- central
Obstructive
-thoracic movement present but airway closed => decreasing SaO2 => disturbed sleep
Central
-no thoracic movement due to neuromuscular/brainstem problems
=> won’t breathe
What is Cheyne Stokes breathing
- what changes
- what can cause this
Rapid cycling of SaO2
- Opioids
- HF
- Stroke
