title: Parasympathetic influence on the arrhythmogenicity of graded dobutamine infusions in halothane-anesthetized horses.
abstract: We investigated the influence of parasympathetic tone on the arrhythmogenicity of graded dobutamine infusions in horses anesthetized under clinical conditions. Six horses were used in 9 trials. Two consecutive series of graded dobutamine infusions were given IV; each continuous graded dobutamine infusion was administered for 20 minutes. The dobutamine infusion dosage (5, 10, 15, and 20 micrograms/kg of body weight/min) was increased at 5-minute intervals. Isovolumetric saline solution vehicle (v) or atropine (A; 0.04 mg/kg) was administered IV, or bilateral vagotomy (VG) was performed as a treatment before the second series of dobutamine infusions. Treatment was not administered prior to the first dobutamine infusion. Significant interaction between treatment and dosage of dobutamine infusion existed for differences from baseline for mean arterial pressure, systolic arterial pressure, diastolic arterial pressure, heart rate, and cardiac index at dosages of 5 and 10 micrograms of dobutamine/kg/min, given IV and for heart rate at dosage of 15 micrograms of dobutamine/kg/min, given IV. Results for group-V horses were different from those for group-A and group-VG horses, but were not different between group-A and group-VG horses in all aforementioned cases, except for heart rate and cardiac index at dosage of 5 micrograms of dobutamine/kg/min, given IV. Normal sinus rhythm, second-degree atrioventricular block, and bradyarrhythmias predominated during low dobutamine infusion rates during the first infusion series (nontreated horses) and in group-V horses during the second infusion series. Only tachyarrhythmias were observed during the second infusion series in the horses of the A and VG groups.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Anatomy, Physiological Sciences, and Radiology, College of Veterinary Medicine, North Carolina State University, Raleigh 27601.
authors.forename: G S
authors.initials: GS
authors.lastname: Light
authors.forename: P W
authors.initials: PW
authors.lastname: Hellyer
authors.forename: C R
authors.initials: CR
authors.lastname: Swanson
mesh_terms: D000758:Anesthesia / Q000662:veterinary*; D000818:Animals; D001145:Arrhythmias, Cardiac / Q000139:chemically induced*; D001794:Blood Pressure / Q000187:drug effects; D004280:Dobutamine / Q000008:administration & dosage / Q000009:adverse effects*; D005260:Female; D006221:Halothane; D006339:Heart Rate / Q000187:drug effects; D006439:Hemodynamics / Q000187:drug effects; D006736:Horses / Q000502:physiology*; D007262:Infusions, Intravenous / Q000662:veterinary; D008297:Male; D010275:Parasympathetic Nervous System / Q000502:physiology*; D011229:Preanesthetic Medication / Q000662:veterinary; D012044:Regression Analysis
chemical_list: D004280:Dobutamine; D006221:Halothane