1. Control of Ventilation
Lectures on respiratory physiology
Control of Ventilation

2. Respiratory control system

3. Diagram showing the pons and medulla oblongata

4. Rhythm controllers in the brainstem
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
Conclusions

5. Other regions of the brain that can affect respiration
Cortex
Can exercise voluntary control
2) Limbic system and hypothalamus
Emotional states
Conclusions

6. Effectors Diaphragm Intercostal muscles Abdominal muscles
4) Accessory muscles
Conclusions

7. Sensors Central chemoreceptor Peripheral chemoreceptors Lung receptors
4) Other receptors
Conclusions

8. Chemoreceptors
Specialized tissues that responds to a change in the chemical composition of the blood or other fluid
Central chemoreceptor
Peripheral chemoreceptors
Conclusions (cont’d)

9. Central chemoreceptor

10. 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
Conclusions (cont’d)

11. Sites of peripheral chemoreceptors

12. Carotid body receptor and its response

13. Carotid bodies Respond to PO2, PCO2 and pH Little response in normoxia
Very high blood flow
Respond to arterial, not venous PO2
Fast response
Conclusions (cont’d)

14. Lung receptors
Pulmonary stretch receptors (also called slowly-adapting pulmonary stretch receptors) Responsible for the Hering-Breuer reflex
Irritant receptors (also called rapidly-adapting pulmonary stretch receptors)
J receptors (juxta-capillary receptors)
4) Bronchial C fibers
Conclusions

15. Other receptors Nose and upper airway Joint and muscle Gamma system
Arterial baroreceptors
Pain and temperature
Conclusions

16. Integrated responses Response to increased PCO2
Response to reduced PO2
Response to changes in pH
4) Response to exercise
Conclusions

17. Ventilatory response to CO2

18. 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
Conclusions (cont’d)

19. Ventilatory response to PO2

20. 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
Conclusions (cont’d)

21. Response to reduced pH Sensed by the peripheral chemoreceptors
Important in metabolic acidosis
If the reduction is severe, central chemoreceptors may be stimulated
Conclusions (cont’d)

22. 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
Conclusions (cont’d)

23. Sleep apnea
Obstructive: very common; often associated with obesity; sleep deprivation may cause daytime somnolence and impaired cognitive function
Central: respiratory depression during sleep; recognized by the absence of respiratory efforts
Conclusions

24. Periodic Breathing at High Altitude
Periodic Breathing at High Altitude (Lahiri)