lectures on respiratory physiology control of ventilation
TRANSCRIPT
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Lectures on respiratory physiologyLectures on respiratory physiology
Control of VentilationControl of Ventilation
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Respiratory control system
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Diagram showing the pons and medulla oblongata
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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
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Other regions of the brain that can affect respiration
1) Cortex
Can exercise voluntary control
2) Limbic system and hypothalamus
Emotional states
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Effectors
1) Diaphragm
2) Intercostal muscles
3) Abdominal muscles
4) Accessory muscles
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Sensors
1) Central chemoreceptor
2) Peripheral chemoreceptors
3) Lung receptors
4) Other receptors
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Chemoreceptors
Specialized tissues that responds to a change in the chemical composition of the blood or other fluid
Central chemoreceptor
Peripheral chemoreceptors
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Central chemoreceptor
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Central chemoreceptor
Responds to pH of ECF
CO2 diffuses across the blood-brain barrier
Normal CSF pH is 7.32
CSF has little buffering
CSF bicarbonate controlled by choroid plexus
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Sites of peripheral chemoreceptors
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Carotid body receptor and its response
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Carotid bodies
Respond to PO2, PCO2 and pH
Little response in normoxia
Very high blood flow
Respond to arterial, not venous PO2
Fast response
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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
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Other receptors1) Nose and upper airway
2) Joint and muscle
3) Gamma system
4) Arterial baroreceptors
5) Pain and temperature
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Integrated responses
1) Response to increased PCO2
2) Response to reduced PO2
3) Response to changes in pH
4) Response to exercise
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Ventilatory response to CO2
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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
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Ventilatory response to PO2
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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
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Response to reduced pH
Sensed by the peripheral chemoreceptors
Important in metabolic acidosis
If the reduction is severe, central chemoreceptors may be stimulated
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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
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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
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Periodic Breathing at High Altitude