Effect of Innovar upon the autonomic control of the heart in intact dog

This experiment compares the regulation of cardiac function in dogs before and after administration of a drug (Innovar-Vet, 0.05 ml/kg) that produces a state of ‘neuroleptanalgesia’. All animals ( n = 21) were chronically instrumented to measure arterial blood pressure (BP) and heart rate (HR); left ventricular pressure (LVP, n = 10) and ascending aortic flow ( n = 4) were also recorded in some animals. After Innovar, the dogs became somnolent and tolerated minor surgical procedures. The p a O 2 decreased (95 ± 11 vs 90 ± 8 mm Hg, pre- vs post-Innovar, mean ± S.D.; P < 0.05) while p a CO 2 increased (33 ± 5 vs 36 ± 5 mm Hg; P < 0.05) when measured ( n = 6) 10 min after drug administration. The changes in HR and BP during a 5-min, left circumflex coronary artery occlusion ( n = 15) were virtually identical in the awake and sedated states; likewise, no significant differences were detected in the occlusion-induced changes in BP, HR, d(LVP) dt and stroke volume in the subset of more fully instrumented dogs. However, some significant effects were seen when the Innovar dose was increased to 5 times normal. The effects of bilateral carotid occlusion and dobutamine infusion (8, 16 and 30 mg/kg) were tested in another 7 dogs. Once again, the analysis of variance interaction terms testing the reflex or drug-induced changes in HR, BP and d(LVP) dt before vs after sedation were not statistically significant. This sedative/analgesic agent has minimal deleterious effects on many aspects of autonomic regulation of the circulation; those effects which can be demonstrated may be tolerable in the study of the regulation of circulation when the totally awake subject cannot be used.