DOBUTAMINE, BUT NOT DOPAMINE, AUGMENTS THE NORMAL CHRONOTROPIC RESPONSE TO ACUTE HYPOXEMIA

Infusion of exogenous dopamine has been shown to alter both the hypoxi c and the hypercapnic ventilatory response, but its effects on the hyp oxic and the hypercapnic cardiac response have not been reported. The purpose of this study was to determine if cardiac responses to hypoxem ia and hypercapnia are altered by infusion of either dopamine (DOP) or its analog dobutamine (DBT). Baseline mean arterial blood pressure (M AP) and heart rate (HR) were measured in 7 normal male subjects while normal saline was infused intravenously (NS1) for 30 min. Each subject then underwent both a eucapnic hypoxemic challenge (EHC), and a hyper oxic hypercapnic challenge (HHC). In a double-blinded randomized fashi on either DOP1 or DBT1 was selected and infused at 5 mug/kg/min for 30 min. EHC and HHC were again performed. This sequence was then repeate d following a second NS infusion (NS2) and the alternate vasopressor. On a second study day, the dose of dopamine (DOP2) selected was that s ufficient to induce a similar rise in MAP as seen with DBT1. Following NS and DOP1 there was a reproducible significant linear increase in H R with progressive hypoxemia seen in all subjects. This response was s ignificantly augmented following infusion of DBT1 (p < 0.03), but no s uch augmentation was noted with DOP2. No significant change in HR was noted during HHC. The mechanisms responsible for this augmentation of hypoxemic response during dobutamine infusion are unclear, and do not appear to be related to a rise in MAP. We speculate that it is due to an effect of dobutamine on beta1-receptor activity.