Download Regulation of Breathing

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RSPT 1207 - CARDIOPULMONARY A&P
REGULATION of VENTILATION
Lecture notes
Reference & Reading: Egan’s pp. 172-174, Chapter 14
I.
Central Nervous System: The CNS will receive stimuli, asses and make a decision
based on the data received and sends command along a motor nerve (neuron) to
the muscles of ventilation.
How the CNS receives stimuli:
II.
CHEMORECEPTORS
a. Central Chemoreceptors
1. Location
2. Blood-brain barrier
3. When CO2 moves across the blood-brain barrier, it goes through
the process of hydrolysis:
CO2 + H2O
4.
5.
6.
7.
8.
H2CO3
HCO3- + H+
The H+ ions that build in the CSF as a result of hydrolysis
By increasing ventilation the PaCO2 reduces
Central chemoreceptors regulate ventilation
Minute Changes
CO2 retention
b. Peripheral Chemoreceptors
1. Location
2. This group of chemoreceptors are sensitive to
 Decreased PaO2 (less than 60 mmHg)
 Increased PaCO2
 Decreased pH (acidosis)
3. Changes in pH must be as large
4. When the Central Chemoreceptors do not respond
5. CO2 retainer
II.
Cerebral Cortex –
a. SOB
1. It is not just triggered by hypercapnia, or hypoxemia.
2. A person who is hypoxic
b. Deliberate Alterations
1. The breathing pattern may be altered
2. As soon as the cerebral cortex ends
How the CNS processes information:
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There are two portions of the lower brain/brainstem that controls ventilation for a
person:
I. Medulla (Oblongata) On the surface of the medulla are two areas:
a. Dorsal Respiratory Groups (DRG):
1. Contains
2. Vagus and glossopharyngeal nerves send sensory impulses to the
DRG
3. These impulses modify the basic breathing pattern in the
medulla
b. Ventral Respiratory Groups (VRG):
1. Location
2. Inspiratory neurons send impulses via the vagus nerve
3. Expiratory neurons sends impulses
II. Pons – the word “pon” literally means bridge.
It takes commands like “I need to swim/talk/ sing” (cerebral cortex)
Into
“Breathe now, hold now” commands (medulla)
a. There are two groups of neurons in the pons:
1. Apneustic Center:
 the function is ill-defined
 Apneustic breathing
2. Pneumotaxic Center: Works with the Apneustic Center to
control the depth of inspiration.
 Strong signals
 Weak signals
How the CNS sends commands:
The spinal cord contain the neural pathways for nerve conduction, both sensation and
motor impulses. They are along the spinal cord and lie within the protection of the spinal
cord.
I. Sensory Nerves
a. Vagus Nerves
 Extends beyond head and neck
b. Glossopharyngeal Nerves
II. Motor Nerves
a. Phrenic Nerves – Breathing commands
 There is a right and left phrenic nerve
 These nerves exit the spinal cord between C3 and C5.
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b. Intercostal Nerves - run along the rib cage.
Breathing Controlled by Reflexes
I.
Hering-Breur Reflex
a. Generated by stretch receptors
b. When lung inflation stretched these receptors
II.
Deflation Reflex
a. deflation reflex results in hyperpnea
b. Signal
III.
Head’s Paradoxic Reflex
a. When the vagus nerve is blocked,
b. Relation to  Vt
IV.
Irritant Receptors
a. Cholinergic Reflex bronchospasm
1. Larger central airways
2. Rapidly adaptive
3. Activated by tactile stimulation
 Inhaled irritants
 Mechanical factors
 Pulmonary congestion
4. Stimulation can result in
 Bronchoconstriction
 Hyperpnea
 Laryngospasm
 Glottis closure
 Coughing
V.
b. Vagovagal Reflex
1. When the reflex has both sensory and motor vagal
components
2. Activated by physical stimulation of conducting airways
 Endotracheal intubation
 Airway suctioning
 Bronchoscopy
3. Stimulation can result in
 bradycardia
 coughing
 laryngospasm
J Receptors
a. Location
b. Activated by
 Alveolar inflammatory responses
 Pulmonary vascular congestions
 Pulmonary edema
c. stimulation results in
 rapid, shallow breathing
 a feeling of dyspnea
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 narrowing of the glottis on exhalation
Abnormal Breathing Patterns
I.
Cheyne-Stokes Breathing
a. Ve increases, reaches a “climax,” then decreases then apnea occurs.
b. Causes
c. Brain is reacting to the acidotic CSF
II.
Biot’s Breathing
a. During regular breathing there is apnea
b. Similar to Cheyne-Stokes,
c. Cause
III.
Apneustic Breathing
a. Cause
b. Persistant Hyperventilation with prolonged inspiratory holds followed
by short exhalations
IV.
Central Neurogenic Hypoventilation
a. Respiratory Centers do not respond to ventilatory stimuli
appropriately
V.
Central Neurogenic Hyperventilation
a. Persistent hyperventilation because the CNS is responding to
abnormal stimuli
b. Related
c. Associated