A 46 years old male patient was given subarachnoid block with bupivacaine (heavy) by the anesthetist. After 10 minutes he was found to have a BP of 72/44 mm Hg and hea rate of 52/min. On checking the level of block it was found to be T6. What is the likely explanation for the bradvcardia?

Ans: A. Bezold-Jarisch reflex (Ref 8/e p1970, Miller 7/e p409)The Bezold-Jarisch reflex involves a variety of cardiovascular and neurological processes which cause hypopnea (excessively shallow breathing or an abnormally low respiratory rate) & bradycardia (abnormally low resting hea rate).Possible cause of profound bradycardia and circulatory collapse after spinal anesthesia.Cardioprotective reflex.Implicated in physiologic response to a range of cardiovascular conditions such as myocardial ischemia or infarction, thrombolysis, or revascularization and syncope.Natriuretic peptide receptors stimulated by endogenous ANP or BNP may modulate the Bezold-Jarisch reflex.Less pronounced in patients with cardiac hyperophy or atrial fibrillation