Respiration - Lecture 5 Flashcards
What is respiratory failure?
when the respiratory system is unable to do its job
What are the 3 ways respiratory failure can occur?
- gas exchanging capabilities
- neural control of ventilation
- neuromuscular breathing apparatus
What is blood hypoxia?
deficient blood oxygenation
What are the levels of PaO2 and % Hb saturation in blood hypoxia?
low PaO2 and low % Hb saturation
What are the 5 general causes of hypoxia?
- inhalation of low PO2 (high altitude)
- hypoventilation
- ventilation imbalance
- 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?
due to disease affecting the CNS, neuromuscular diseases, barbiturates and other drugs/narcotics
How does ventilation imbalance in the lungs occur?
when the amount of fresh gas reaching an alveolar region per breath is too little for the blood flow through the capillaries of that region
What happens to venous blood during shunts of blood across the lungs?
it bypasses the gas exchange region of the lungs and returns to systemic circulation, deoxygenated
What is an example of shunts of blood across the lungs?
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 involuntary control
Which neurological structures control voluntary breathing?
the cerebral hemispheres
Which neurological structures control involuntary breathing?
the brainstem (pons + medulla)
What happens when you stop ventilation voluntarily?
breathing will eventually start again
What is the breaking point?
when arterial PCO2 and PO2 has reached levels where voluntary control is over-ridden
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
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 lung volume and O2/CO2 content
What are the two kinds of sensors?
pulmonary receptors and chemoreceptors
How is information sent to controllers?
via afferent 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?
the respiratory muscles
Why are neuronal impulses sent to effectors?
so that ventilation can be adjusted to the person’s metabolic needs
Where are the pacemakers cells located?
the ventral respiratory group of the medulla
What is the function of the ventral respiratory group?
they generate the basic rhythm
What does the ventral respiratory group contain?
pre-Botzinger complex
What is the function of the dorsal respiratory group?
they receive several sensory inputs
What do the cells in the ventral and dorsal respiratory group connect to?
inspiratory motor neurons
What kind of rhythmicity do the respiratory neurons in the medulla generate?
the basic respiratory rhythmicity
What kind of cells are found in the medulla?
pacemaker cells
What is another name for the upper pons?
the pneumotaxic centre
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 turns off inspiration?
tidal volume: becomes smaller
breathing frequency: increases
What happens to breathing when the pneumotaxic centres are cut?
it becomes deep and slow
What happens to breathing when the vagus nerves are cut?
it becomes deep and slow
What is another name for the lower pons?
the apneustic centre
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?
inspiration
What happens when you remove the upper pons and the vagus nerve?
apneuses
What kind of breathing is seen in some severe types of brain injury?
apneuses
What is apneuses?
tonic inspiratory activity interrupted by short expirations
What do chemoreceptors detect?
PO2, PCO2 and pH in arterial blood
Where is information from the chemoreceptors carried to?
to the respiratory neurons
When will the activity of respiratory neurons increase?
- PaO2 <60mmHg
- PaCO2 >40 mmHg
When will the activity of respiratory neurons decrease?
- PaO2 > 100 mmHg
- PaCO2 < 40 mmHg
What are the two kinds of chemoreceptors?
central and peripheral
Where are central chemoreceptors located?
on the ventral surface of the medulla
What do the central chemoreceptors detect?
the pH of the cerebrospinal fluid surrounding them
What is the pH of the CSF surrounding the central chemoreceptors influenced by?
the 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?
by a CO2 rebreathing test
What happens during a CO2 rebreathing test?
a subject breathes different CO2 mixtures or rebreathes expired air from a bag filled with O2 so that with each expiration, the inspired PCO2 gradually increases
What happens when the chemoreceptors are stimulated during the CO2 rebreathing test?
minute ventilation increases, hyperventilation, decrease in PCO2 in the blood and CSF
What kind of relationship is there between ventilation and PCO2 in central chemoreceptors?
linear
What are peripheral chemoreceptors mainly sensitive to?
changes in PO2
What are peripheral chemoreceptors stimulated by?
increased PCO2 and decreased pH
Where are peripheral chemoreceptors located?
in carotid bodies (the bifurcation of the common carotid arteries) and in the aortic bodies (next to the ascending aorta)
What are the carotid and aortic bodies made up of?
blood vessels, structural supporting tissue and nerve endings of sensory neurons of the glossopharyngeal and vagus nerve
What two nerves make up the carotid and aortic bodies?
the glossopharyngeal and vagus nerves
Where do the afferent fibers of the peripheral chemoreceptors projected?
to the dorsal group of the respiratory neurons in the medulla
How can the sensitivity of peripheral chemoreceptors be assessed?
by having a subject breathe gas mixtures with decreased concentrations of O2
What pressure does O2 have to be in order to have an appreciable change in minute ventilation?
60 mmHg
At increased PCO2, a decrease of PO2 below ___ can already cause an increase in minute ventilation.
100 mmHg
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 receptos
- j receptors
Where do the afferent fibres of the receptors that respond to mechanical stimuli travel?
in the vagus nerves
Where are pulmonary stretch receptors located?
in smooth muscles 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 of the lung
When does the activity of the stretch receptors increase?
as lung volume increases during each inspiration
What is the reflex that stimulates pulmonary stretch receptors?
the Hering-Breuer Inflation Reflex
What is the Hering-Breuer Inflation Reflex?
a decrease in respiratory frequency due to a prolongation of expiratory time
Where is Hering-Breuer Inflation Reflex noticeable?
in infant and animals
Where are the irritant receptors located?
between airway epithelial cells in the trachea down to the respiratory bronchioles
What are the irritant receptors stimulated by?
noxious gases, cigarette smoke, histamine, cold air and dust
What are irritant receptors innervated by?
myelinated fibers
What happens when irritant receptors are stimulated?
bronchoconstriction and hyperpnea happens
What are irritant receptors important in?
the reflex bronchoconstriction triggered by histamine release during an allergic asthmatic attack
Where are the junta-capillary receptors found?
in the alveolar walls 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
What are juxta-capillary receptors stimulated by?
an increase in pulmonary interstitial fluid
What are the reflexes caused by the juxta-capillary receptors?
rapid and shallow respiration and apnea
What do juxta-capillary receptors play a role in?
dyspnea associated with left heart failure and lung edema or congestion
What does minute ventilation increase linearly with?
VO2
What happens to minute ventilation when exercise increases?
it increases
What happens to arterial PO2 when exercise increases?
it remains constant
What happens to arterial PCO2 when exercise increases?
it stays constant then decreases
What happens to pH when exercise increases?
it increases
The role of the central chemoreceptors is important at ___ but not so much during ___.
rest, exercise
What increases the sensitivity of the peripheral chemoreceptors to CO2 and H+ during exercise?
fluctuations in PaO2
