CONTROL OF VENTILATION

Joanne Simpson

Basic Sub-groups

Central Controller

EffectorsSensors

Input Output

Central Controller

Brainstem

Medullary Respiratory CentreDorsal Respiratory Group (Inspiration) – responsible for

basic ventillatory rhythmExpiratory Area – Used for forceful breathing

Apneustic CentreLower Pons - Impulses from here have excitatory effect

on the inspiratory area of the medulla

Pneumotaxic CentreUpper Pons – regulates volume and rate of respiration

(fine tuning)

Cortex

Can override the function of the brainstem within limits

Able to voluntarily halve PCO2 by hyperventillation causing alkalosis

Duration of breath holding limited by many factors. Primarily PO2 and PCO2

Other Parts of the Brain

The Limbic System and Hypothalamus can alter the pattern of breathing in affective states such as rage and fear

Effectors

Effectors Muscles of the diaphragm Intercostal Muscles Abdominal Muscles Accessory Muscles

Co-ordinated action is the responsibility of the central controller.

Sensors

Central Chemoreceptors Surrounded by brain ECF and respond

to changes in H+ concentration, (↓ [H+] suppresses ventillation)

Composition of ECF controlled by surrounding CSF, local blood flow and metabolism

Buffering effect, (↑[CO2] means ↑ liberation of H+ and resulting hyperventilation)

Peripheral Chemoreceptors Found in the

carotid bodies chiefly

Respond to decreases in PO2 and pH, and increases in PCO2

↓PO2 results in ↑Ventilation

↓pH results in ↑Ventilation

Lung Receptors Pulmonary Stretch ReceptorsStretching of lungs causes firing of receptor and feedback

via the vagus ↓respiratory frequency by ↑ expiration time

Irritant ReceptorsStimulated by noxious gases, smoke and cold air. Impulses

travel up the vagus causing bronchoconstriction and hyperpnea

J ReceptorsRespond to chemicals in the lungs. Impulses travel up the

vagus and cause rapid, shallow breathing and dyspnoea

Other Receptors Nose and Upper Airway ReceptorsSimilar to irritant receptors, initiate coughs/sneezes Joint and Muscle ReceptorsImpulses from moving limbs are thought to ↑ ventillation in

early stages Gamma SystemMuscle spindles that sense elongation of the muscle, therfore

giving sensation of dyspnoea if a large respiratoy effort is required to move chest wall

Arterial Baroreceptors↑Arterial BP may cause hypoventillation / apnoea – converse

is true Pain and TemperatureStimulus may cause hyperventillation

Questions?