Lectures on respiratory physiology Control of Ventilation

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 p. H of ECF CO 2 diffuses across the bloodbrain barrier Normal CSF p. H 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 PO 2, PCO 2 and p. H Little response in normoxia Very high blood flow Respond to arterial, not venous PO 2 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 PCO 2 2) Response to reduced PO 2 3) Response to changes in p. H 4) Response to exercise

Ventilatory response to CO 2

Response to CO 2 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 PO 2

Response to reduced PO 2 No role under normoxic conditions Measured by rebreathing from a bag Increased response if the PCO 2 is raised Important at high altitude Important in some patients with chronic lung disease

Response to reduced p. H 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 p. H is normal except at heavy exercise ? Cortex, impulses from limbs, increased temperature, resetting of CO 2 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