Cardiac Reflexes

Describe the cardiac reflexes

Cardiac reflexes are fast-acting reflex loops between the CVS and CNS which contribute to the maintenance of cardiovascular haemostasis.

They include:

  • Baroreceptor reflex
    Aortic arch and carotid sinus reflexes.
  • Bainbridge reflex
    Atrial stretch receptor reflexes.
  • Chemoreceptor reflex
    Decreased PaO2 < 50mmHg or decreased pH sensed by peripheral chemoreceptors causes subsequent tachycardia and hypertension.
  • Cushing reflex
    Brainstem compression causes ischaemia of the vasomotor centre leading to Cushings' Triad:
    • Hypertension
      May have a wide pulse pressure.
    • Bradycardia
      Due to baroreceptor response from hypertension.
    • Irregular respirations
  • Bezold-Jarisch reflex
    Stimulation of C fibres of the vagus nerve in the cardiopulmonary region.
    • This causes:
      • Significant bradycardia
      • Hypotension
      • Apnoea, followed by rapid shallow breathing. These fibres can be stimulated by a number of substances, including:
    • Capsaicin
    • Serotonin
    • Those produced in myocardial ischaemia
  • Oculocardic reflex
    Pressure on the globe or traction on ocular muscles causes a decrease in heart rate. This is mediated by the:
    • Trigeminal nerve (afferent limb)
    • Vagus nerve (efferent limb)
      Increased vagal tone reduces SA nodal activity.

References

  1. CICM September/November 2013
  2. Barrett KE, Barman SM, Boitano S, Brooks HL. Ganong's Review of Medical Physiology. 24th Ed. McGraw Hill. 2012.
  3. Open Anaesthesia - Oculocardiac reflex: afferent path
Last updated 2018-03-04

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