Dexmedetomidine and hemodynamic responses to simulated hemorrhage in experimental heart failure

alpha (2)-Adrenoreceptor agonists may counteract the increased basal sympat hetic nervous activity in patients with congestive heart failure (CHF), but they may also compromise reflex responses to hypovolemia. We have tested r esponses to simulated hemorrhage (central hypovolemia) after IV dexmedetomi dine in normal animals and in experimental chronic CHF. Rabbits (n = 14) we re treated with IV doxorubicin (or control saline) for 8 weeks inducing biv entricular dilatation and myocardial damage. Cardiac output (CO) was measur ed continuously with. a transit-time Doppler implanted on the ascending aor ta. Progressive inflation of a cuff around the inferior vena cava (simulate d hemorrhage) was used to reduce cardiac index ata constant rate. Arterial baroreceptor-mediated vasoconstrictor and heart rate responses were tested with repeated cuff inflations. Although resting CO was reduced in CHF, the blood pressure and heart rate changes with dexmedetomidine were not exagger ated. The slope of the vasoconstrictor response to graded hypovolemia was a ttenuated by dexmedetomidine with an earlier onset of decompensation. There was no added effect of CHF on the response until the dose of dexmedetomidi ne was sufficient to reduce resting CO in addition to arterial blood pressu re and heart rate.