Expansion
Bainbridge speeds the heart with atrial stretch; Bezold-Jarisch slows it
Expansion
Bainbridge reflex
- Trigger: stretch of atrial receptors by increased venous return
- Effect: increased heart rate
- Purpose: to prevent damming of blood in the veins when return rises
- Contributes to the inspiratory quickening of sinus arrhythmia
Bezold-Jarisch reflex
- Trigger: stimulation of ventricular mechanoreceptors and chemoreceptors, classically by a vigorously contracting but underfilled ventricle
- Effect: bradycardia, vasodilatation and hypotension, through vagal afferents
- Implicated in vasovagal syncope, in the bradycardia of inferior myocardial infarction, and in sudden bradycardia during spinal anaesthesia or haemorrhage
The Bezold-Jarisch reflex is the counterintuitive one: profound bradycardia in the face of hypovolaemia, exactly when tachycardia would be expected. Recognising it explains why some patients bleeding into the abdomen present with a slow pulse.