Respiration lecture 5 Flashcards
What is respiratory failure?
when the respiratory system is unable to do it’s job properly
What are the 3 ways respiratory failure can occur?
- failure of the gas-exchanging capabilities of the lungs
- Failure of the neural control of ventilation
- Failure of the neuromuscular breathing apparatus
What is blood hypoxia?
deficient blood oxygenation described as low PaO2 and low percentage of Hb saturation
What are the 5 general causes of hypoxia?
- Inhalation of low PO2 (high altitude)
- Hypoventilation
- Ventilation/perfusion imbalance in the lungs
- Shunts of blood across the lungs
- O2 diffusion impairment
What happens to PaO2 and PaCO2 during hypoventilation?
PaO2 decreases and PaCO2 increases
How does hypoventilation happen?
It’s when the alveolar ventilation in relation to the metabolic CO2 production reduces
What happens to venous blood during shunts of blood across the lungs?
Venous blood bypasses the gas-exchanging area and returns to the systemic circulation deoxygenated.
What is an example of shunts of blood across the lungs?
patent foramen ovale
What are 2 examples of O2 diffusion impairment?
THickening of the alveolar/capillary membrane or pulmonary edema
What kind of control is breathing under?
Voluntary and autonomic control
Which neurological structures control voluntary breathing?
Cerebral hemispheres
Which neurological structures control involuntary breathing?
Brainstem: pons and medulla
What happens when you stop ventilation voluntarily?
the involuntary system will take over and you will start breathing again
What is the breaking point?
It is when voluntary control is over-ridden when PACO2 and PAO2 have reached certain levels
What does over-riding of the voluntary control by the automatic control depend upon?
the information from the receptors sensitive to CO2 and O2 levels in arterial blood and CSF
What are the 3 basic elements in the respiratory control system?
Sensors, controllers and effectors
What is the function of sensors?
They gather information about the lung volume and CO2/O2 levels
What are the two kinds of sensors?
Pulmonary receptors and chemoreceptors
How is information sent to controllers?
Via neural fibres
Where are controllers located?
in the pons and medulla
What happens when information has reached the pons and medulla?
the peripheral information and inputs from the higher structures of the CNS are integrated
What is another name for effectors?
respiratory muscles
Why are neuronal impulses sent to effectors?
so that ventilation can be adjusted to the person’s metabolic needs determined by the sensors and controllers
Where are the repiratory pacemaker cells located?
the ventral respiratory group of the medulla
What is the function of the ventral respiratory group of the medulla?
To generate the basic rhythm of breathing
What does the ventral respiratory group contain?
pacemaker cells
What is the function of the dorsal respiratory group?
it receives several sensory inputs
What do the cells in the ventral and dorsal respiratory group connect to?
inspiratory motor neurons
What kind of cells are found in the medulla?
pacemaker cells
What does the medulla do? how is it affected in the absence of the vagus nerve?
It generates the basic respiratory rhythmicity. Without the vagus nerve, the rhythmicity is the same but with no control of the lung volume
What is the function of the upper pons?
it modifies the inspiratory activity of the centres in the medulla
Does the upper pons turn on or turn off inspiration?
turn off
What happens to the tidal volume and breathing frequency when the upper pons turn off inspiration (when the upper pons are functioning)?
tidal volume: becomes smaller
breathing frequency: increases
What happens to breathing when the upper pons are cut?
Breathing becomes slow and deep (no more inhibition of inspiration)
What happens to breathing when the vagus nerves are cut on an intact brainstem?
It has the same effect as removing the upper pons meaning that breathing will be slow and deep
What s the function of the cells located in the lower pons?
They send excitatory impulses to the respiratory groups of the medulla
What does the lower pons promote?
They promote inspiration
What happens when you remove the upper pons and the vagus nerve?
It causes apneuses, seen in some severe types of brain injuries
What is apneuses?
tonic inspiratory activity interrupted by short expirations –> prolonged inspiratory phase followed by an irregular and inadequate expiration
What do chemoreceptors detect?
PO2, PCO2 and pH in arterial blood
Where is information from the chemoreceptors carried to?
the respiratory neurons
At what levels of O2 and CO2 will the activity of respiratory neurons increase?
if PaO2 is lower than 60 mmHg
if PaCO2 is greater than 40 mmHg
When will the activity of respiratory neurons decrease?
if PaO2 is greater than 100 mmHg
if PaCO2 is lower than 40 mmHg
What are the two kinds of chemoreceptors?
Central chemoreceptors and Peripheral chemoreceptors
Where are central chemoreceptors located?
in the ventral surface of the medulla
What do the central chemoreceptors detect?
the pH of CSF
What is the pH and PCO2 of the CSF surrounding the central chemoreceptors influenced by?
by the pH and PCO2 of the arterial blood
What do the central chemoreceptors give rise to?
the main drive to breathe under normal conditions
How can the sensitivity of central chemoreceptors be assessed?
with a CO2 rebreathing test
What happens during a CO2 rebreathing test?
Breathing different mixtures of CO2 or rebreathing expired from a bag filled with O2
What happens when the chemoreceptors are stimulated during the CO2 rebreathing test?
When the pH of the CSF is reduced due to increased CO2, the chemoreceptors are stimulated to increase ventilation
What kind of relationship is there between ventilation and PCO2 in central chemoreceptors?
it is a linear relationship where minute ventilation will increase as soon as PaCO2 increases
From the variables responsible for minute ventilation (Ve=Tv x frequency), which is responsible for increased minute ventilation when PCO2 is elevated?
The tidal volume and the frequency increases
How do the central chemoreceptors work?
Only the CO2 can cross the blood-brain barrier and go into the CSF. Once it has crossed it will go through reactions to make HCO3- and H+. This will decrease the pH of CSF detected by the receptors and increase ventilation. (vice-versa)
What are peripheral chemoreceptors mainly sensitive to?
changes in PO2
What are peripheral chemoreceptors secondarily stimulated by?
increases PCO2 and decreased pH
Where are peripheral chemoreceptors located?
in the carotid bodies and the aortic bodies
What are the carotid and aortic bodies made up of?
blood vessels structural supporting tissue and nerve ending of sensory neurons
What two nerves make up the carotid and aortic bodies?
Carotid: glossopharyngeal nerve (IX)
Aortic: vagus nerve (X)
Where do the afferent fibers of the peripheral chemoreceptors projected?
the the dorsal group of the respiratory neuron in the medulla
How can the sensitivity of peripheral chemoreceptors be assessed?
by having subjects breathe gas mixtures with decreased concentrations of O2
What pressure does O2 have to be to have an appreciable change in minute ventilation when PCO2 is not increased?
60 mmHg
Increasing PCO2, ___ ventilation at ___
increases
any PO2
An ___ in PCO2 and a ___ in PO2 interact giving an augmented ventilatory response
increase
decrease
What are the 3 kinds of receptors in the lungs that respond to mechanical stimuli?
Pulmonary stretch receptors
Irritant receptors
Juxta-capillary receptors (J receptors)
Where do the afferent fibres of the receptors that respond to mechanical stimuli travel?
in the vagus nerve
Where are pulmonary stretch receptors located?
in the smooth muscle of the trachea down to the terminal bronchioles
What are pulmonary stretch receptors innervated by?
large, myelinated fibres
When do pulmonary stretch receptors discharge?
in response to distension (larger) of the lung
When does the activity of the stretch receptors increase?
as the lung volume increases during each inspiration
What is the reflex that pulmonary stretch receptors activate?
the Hering-Breuer inflation reflex
What is the Hering-Breuer Inflation Reflex?
a decrease in respiratory frequency due to prolonged expiratory time (if the lungs expand increases, the beginning of the next inspiratory effort will be inhibited)
Where is the Hering-Breuer Inflation Reflex noticeable? WHere is it not noticeable?
in weak adults unless tidal volume exceeds 1L like in exercises. It is not noticeable in infants and animals
Where are the irritant receptors located?
between airway epithelial cells in the trachea down the respiratory bronchiloes
What are the irritant receptors stimulated by?
noxious gases
cigarette smoke
histamine
cold air
dust
What are irritant receptors innervated by?
myelinated fibres
What happens when irritant receptors are stimulated?
bronchoconstriction and hyperpnea (increased breathing depth
What are irritant receptors important in?
in the reflex bronchoconstriction triggered by histamine release during an allergic asthmatic attack
Where are the junta-capillary receptors found?
In the alveolar wall close to the capillaries
What innervates the juxta-capillary receptors?
non-myelinated fibres
What kind of activity do the juxta-capillary receptors have?
short-lasting bursts of activity
What are juxta-capillary receptors stimulated by?
an increase in pulmonary interstitial fluid (pulmonary congestion and edema)
What are the reflexes caused by the juxta-capillary receptors?
rapid and shallow respiration, intense stimulation causes apnea
What do juxta-capillary receptors play a role in?
feelings of dyspnea (difficulty breathing) associated with left heart failure and lung edema or congestion
What does minute respiration increase linearly within all individuals?
Metabolic rate
What happens to minute ventilation when exercise increases?
it goes up to 50% - 65% of VO2 max. After there is hyperventilation starting
What happens to arterial PO2 when exercise increases?
increase in PO2
What happens to arterial PCO2 when exercise increases?
decrease in PCO2
What happens to pH when exercise increases?
decrease in pH
The role of the central chemoreceptors is important at ___ but not so much during ___. Why?
rest
exercise
Because even if exercise causes an increase in arterial pH, H+ doesn’t cross the blood-brain barrier and so can’t be detected by the central chemoreceptors
A modification in the enviromnment will cause the receptors to react (high CO2 air)
What increases the sensitivity of the peripheral chemoreceptors to CO2 and H+ during exercise?
The fluctuations of PaO2
