Lectures on respiratory physiology Control of Ventilation.

Lectures on respiratory physiologyLectures on respiratory physiology

Control of VentilationControl 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 blood-brain 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 receptors1) 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