Lectures on respiratory physiology
Control of Ventilation
Respiratory control system
Diagram showing the pons and medulla oblongata
Rhythm controllers in the
brainstem
1) Medulla
Dorsal respiratory group – associated with inspiration
Ventral respiratory group – associated with expiration.
Pre-Botzinger Complex - pattern generator, also ventral
2) Pons
Apneustic center – has an excitatory function
Pneumotaxic center
– can inhibit inspiration
Other regions of the brain that
can affect respiration
1) Cortex
Can exercise voluntary control
2)
Limbic system and hypothalamus
Emotional states
Effectors
1) Diaphragm
2) Intercostal muscles
3) Abdominal muscles
4) Accessory muscles
Sensors
1) Central chemoreceptor
2) Peripheral chemoreceptors
3) Lung receptors
4) Other receptors
Chemoreceptors
Specialized tissues that responds to a change in
the chemical composition of the blood or
other fluid
Central chemoreceptor
Peripheral chemoreceptors
Central chemoreceptor
Central chemoreceptor
Responds to pH of ECF
CO2 diffuses across the bloodbrain barrier
Normal CSF pH is 7.32
CSF has little buffering
CSF bicarbonate controlled by
choroid plexus
Sites of peripheral chemoreceptors
Carotid body receptor and its response
Carotid bodies
Respond to PO2, PCO2 and pH
Little response in normoxia
Very high blood flow
Respond to arterial, not venous PO2
Fast response
Lung receptors
1) Pulmonary stretch receptors
(also called
slowly-adapting pulmonary stretch receptors)
Responsible for the Hering-Breuer reflex
2) Irritant receptors (also called rapidly-adapting
pulmonary stretch receptors)
3) J receptors (juxta-capillary receptors)
4) Bronchial C fibers
Other receptors
1) Nose and upper airway
2) Joint and muscle
3) Gamma system
4) Arterial baroreceptors
5) Pain and temperature
Integrated responses
1) Response to increased PCO2
2) Response to reduced PO2
3) Response to changes in pH
4)
Response to exercise
Ventilatory response to CO2
Response to CO2
Primary factor in the control of ventilation
Measured by rebreathing from a bag
Inspiratory pressure following brief occlusion
Response is altered by sleep, age, genetic factors
Reduced by increasing the work of breathing
Ventilatory response to PO2
Response to reduced PO2
No role under normoxic conditions
Measured by rebreathing from a bag
Increased response if the PCO2 is raised
Important at high altitude
Important in some patients with chronic lung disease
Response to reduced pH
Sensed by the peripheral chemoreceptors
Important in metabolic acidosis
If the reduction is severe, central chemoreceptors
may be stimulated
Response to exercise
Blood gases are normal
pH is normal except at heavy exercise
? Cortex, impulses from limbs, increased
temperature, resetting of CO2
reference level
Sleep apnea
1) Obstructive: very common; often
associated with obesity; sleep deprivation
may cause daytime somnolence and
impaired cognitive function
2) Central: respiratory depression during
sleep; recognized by the absence of
respiratory efforts
Periodic Breathing at High Altitude