16. Cardiorespiratory Interactions

• inspiration = increased heart rate
• inspiration = increased venous return to right ventricle
• inspiration = increased stroke volume
• inspiration = increased left EDV
• respiratory sinus arrhythmia = increased heart rate during inspiration

  • due to changes in vagal activity
  • central inspiratory neurones inhibit cardiac vagal neurone activity
  • phrenic nerve activity rises as you inspire
• two main mechanisms cause respiratory sinus arrhythmia:

  • central nervous mechanism
  • reflex mechanism

  both involved the nucleus ambiguous
• central nervous mechanism of respiratory sinus arrhythmia:

  • central inspiratory drive is active during inspiration
  • excites the inspiratory motor neurones which excite the phrenic nerves
  • inhibits the nucleus ambiguous
  • leads to the vagal nerve being inhibited
  • causing heart rate to increase
• reflex mechanism of respiratory sinus arrhythmia:

  • during inspiration, inspiratory motor neurones are activated and the airways widen
  • stimulate pulmonary stretch receptors
  • leads to activation of the NTS
  • this inhibits the NA which increases HR
• the diving reflex is invoked by trigeminal receptors - cold water on face/nose

  • leads to reflex inhibition of central inspiratory neurones
  • cause expiratory apnoea and decreased HR
  • cause vasoconstriction