Responses of blood flow, oxygen consumption, and contractile function to inotropic stimulation in stunned canine myocardium.
To examine the effects of inotropic stimulation on regional myocardial blood flow (MBF), oxidative metabolism, and contractile function in stunned myocardium, nine closed-chest dogs were studied 2 hours postreperfusion after a 25 minute occlusion of the left anterior descending coronary artery (LAD). MBF was determined with microspheres, and regional myocardial oxygen consumption (MVO2) was estimated from the rate constant k1 of the rapid clearance phase of [1-11C] acetate time activity curves, recorded with dynamic positron emission tomography. Myocardium at risk was determined from [13N] ammonia images obtained during occlusion. Wall motion, assessed by two-dimensional echocardiography, was impaired in postischemic myocardium in all dogs 2 hours after reperfusion. Dobutamine infusion increased the rate pressure product by 70% +/- 31% and significantly improved contractile function in the postischemic region in all dogs. In remote myocardium, MVO2 increased from 5.7 +/- 1.2 to 8.6 +/- 1.6 mumol/gm/min, and blood flow from 0.87 +/- 0.16 to 1.52 +/- 0.42 ml/gm/min in response to dobutamine. In reperfused myocardium, MVO2 increased from 3.1 +/- 0.7 to 7.4 +/- 1.5 mumol/gm/min, and blood flow from 0.51 +/- 0.12 to 1.2 +/- 0.4 ml/gm/min. Oxygen extraction increased significantly in reperfused myocardium relative to remote myocardium consistent with a flow-limited response to dobutamine stimulation. The improvement in contractile function failed to correlate significantly with relative increases in MBF or MVO2, suggesting that mechanical function is not as tightly coupled as MBF and MVO2 in postischemic myocardium during inotropic stimulation.
Hashimoto
T
T
Department of Molecular and Medical Pharmacology, University of California-Los Angeles School of Medicine.
Buxton
D B
DB
Krivokapich
J
J
Hansen
H W
HW
Phelps
M E
ME
Schelbert
H R
HR
D000704:Analysis of Variance; D000818:Animals; D003326:Coronary Circulation / Q000187:drug effects* / Q000502:physiology; D004280:Dobutamine / Q000008:administration & dosage; D004285:Dogs; D004452:Echocardiography / Q000379:methods / Q000706:statistics & numerical data; D016018:Least-Squares Analysis; D008863:Microspheres; D009200:Myocardial Contraction / Q000187:drug effects* / Q000502:physiology; D015425:Myocardial Reperfusion / Q000706:statistics & numerical data; D017682:Myocardial Stunning / Q000175:diagnosis / Q000453:epidemiology / Q000503:physiopathology*; D010101:Oxygen Consumption / Q000187:drug effects* / Q000502:physiology; D012815:Signal Processing, Computer-Assisted / Q000295:instrumentation; D013268:Stimulation, Chemical; D014055:Tomography, Emission-Computed / Q000295:instrumentation / Q000379:methods / Q000706:statistics & numerical data; D014915:Whole-Body Counting / Q000295:instrumentation / Q000379:methods / Q000706:statistics & numerical data
D004280:Dobutamine