CONTROL OF VENTILATION

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CONTROL OF VENTILATION

• Joanne Simpson

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Basic Sub-groups
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Central Controller
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Brainstem

• Medullary Respiratory Centre
• Dorsal Respiratory Group (Inspiration)
  responsible for basic ventillatory rhythm
• Expiratory Area Used for forceful breathing
• Apneustic Centre
• Lower Pons - Impulses from here have excitatory
  effect on the inspiratory area of the medulla
• Pneumotaxic Centre
• Upper Pons regulates volume and rate of
  respiration (fine tuning)

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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

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Other Parts of the Brain

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

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Effectors
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Effectors

• Muscles of the diaphragm
• Intercostal Muscles
• Abdominal Muscles
• Accessory Muscles
• Co-ordinated action is the responsibility of the
  central controller.

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Sensors
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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)

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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

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Lung Receptors

• Pulmonary Stretch Receptors
• Stretching of lungs causes firing of receptor and
  feedback via the vagus ?respiratory frequency by
  ? expiration time
• Irritant Receptors
• Stimulated by noxious gases, smoke and cold air.
  Impulses travel up the vagus causing
  bronchoconstriction and hyperpnea
• J Receptors
• Respond to chemicals in the lungs. Impulses
  travel up the vagus and cause rapid, shallow
  breathing and dyspnoea

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Other Receptors

• Nose and Upper Airway Receptors
• Similar to irritant receptors, initiate
  coughs/sneezes
• Joint and Muscle Receptors
• Impulses from moving limbs are thought to ?
  ventillation in early stages
• Gamma System
• Muscle 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 Temperature
• Stimulus may cause hyperventillation

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Questions?