The American journal of physiology
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The heart rate response to hemorrhage was studied in conscious dogs before and up to 2 mo after the establishment of volume overload due to systemic arteriovenous (a-v) fistulas. Before a-v fistula, heart rate increased markedly during hemorrhage. When hemorrhage was preceded by dextran infusion, bleeding resulted in a gradual reduction in heart rate. ⋯ The response was observed as early as 5 days after a-v fistula. We conclude that an alteration in the heart rate response to hemorrhage appears early during volume overload. This alteration appears to be reflex in nature and to be mediated by the parasympathetic nervous system.