During acute hemorrhage, the Bainbridge reflex and Bezold-Jarisch reflex differ in their hemodynamic effects as follows:
- A Both reflexes increase heart rate to compensate for reduced cardiac output
- B Bainbridge reflex is activated by hypoxia; Bezold-Jarisch by increased venous return
- C Bainbridge increases heart rate when right atrial pressure rises; Bezold-Jarisch causes paradoxical bradycardia and hypotension in response to reduced ventricular volume ✓
- D Bezold-Jarisch increases heart rate; Bainbridge causes bradycardia
Correct answer: C. Bainbridge increases heart rate when right atrial pressure rises; Bezold-Jarisch causes paradoxical bradycardia and hypotension in response to reduced ventricular volume
Explanation
The Bainbridge reflex is triggered by distension of the right atrium and great veins, causing reflex tachycardia via vagal afferents to the medulla, thus increasing heart rate when venous return rises. The Bezold-Jarisch reflex is triggered by mechanical deformation of ventricular mechanoreceptors (C-fibers) especially during marked ventricular volume depletion, causing paradoxical bradycardia, vasodilation, and hypotension — a potential mechanism for vasovagal syncope in hemorrhage. These reflexes thus have opposing effects on heart rate.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
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