PHYL3002 Lecture Notes - Lecture 4: Tachypnea, Laryngospasm, Shortness Of Breath
LECTURE FOUR: Respiratory Reflexes
Central Control of Ventilation:
• Rhythm generated in medulla
• Modified by pons and afferent input
• Peripheral receptor modify ventilation
• Temperature stimulates ventilation (panting)
• Emotion can produce respiratory effects (sigh, gasp)
• Separate voluntary control
Hering-Breuer Reflex:
• Section of vagus increases depth of breathing and prolongs inflation time
• Hooke → 1660s → forced inspiration stopped respiratory effort
• Beruer → 1868 → demonstrated Hering-Breuer reflex
• Lung inflation inhibits inspiratory drive
• Vagal reflex mediated by stretch receptors located in lungs
• Potent reflex in many animals but weak in humans
• Little effect on breathing in conscious humans → nerve block with local
anesthetics
Lower Airway Receptors:
• Slowly adapting receptors (SAR)
o Volume related
o Lung stretch receptors in muscle
o Hering-Breuer reflex limits inspiration
• Rapidly adapting receptors (RAR)
o Mechano/irritant
o Within or near epithelium
o Reflexes → rapid shallow breathing, hyperventilation,
bronchoconstriction, cough
• C-Fiber afferents
o Ramify in airway epithelium
o Respond to tissue damage (pain fibers) and irritants
o Produces → bronchoconstriction, bradycardia, apnoea
• Axon reflex
o C-fiber contains neurotransmitters → tachykinins (peptides)
o Release non-adrenergic non-cholingeric transmitters (e.g.
substance P, neurokinin A)
o Stimulated by vascular leak → increase gaps between cells,
leaking out of plasma proteins → oedema
o Mucous production leading to bronchoconstriction
Slowly Adapting Receptors:
• SAR measure lung volume from stretch of airway wall
• Little adaptation to stretch → firing rate stays high
• Myelinated nerves (B-fibers, A�-fibers)
• 15-30m/s conduction velocity
• Active in normal tidal breathing
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