Circulation research
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Circulation research · Aug 1975
Reduced baroreflex sensitivity with volume loading in conscious dogs.
The Bainbridge reflex, i.e., the effect of rapid saline infusion (1.1 +/- 0.1 liters) on heart rate and arterial and atrial blood pressures, was examined in 12 intact conscious dogs; mean arterial blood pressure rose by 33 +/- 3 (SE) mm Hg, mean atrial pressure by 14 +/- 1 mm Hg, and heart rate by 75 +/- 9 beats/min. After beta-receptor blockade, heart rate rose slightly less (+49 +/- 5 beats/min, P = 0.05). Cholinergic blockade, combined cholinergic and beta-receptor, or beta-receptor blockade after vagotomy blocked the heart rate response to the infusion. ⋯ After a mild amount of volume loading, when atrial pressure was 8 +/- 2 mm Hg, the PI/SAP slope was significantly depressed from normal. When atrial pressure was elevated further to 28 +/- 1 mm Hg by volume loading, the slope was further depressed. Thus, arterial baroreflex sensitivity is reduced progressively as atrial pressure is raised by volume loading, an observation that explains how heart rate can rise strikingly in the face of an elevated arterial blood pressure.