Blood flow distribution within skeletal muscle during exercise in the presence of chronic heart failure: effect of milrinone.

Recent studies suggest that, in the presence of heart failure, the capability of skeletal muscle to utilize delivered flow may be impaired due to maldistribution of blood flow within working muscle. Similarly, this mechanism could explain the failure of drugs to improve maximal oxygen consumption (VO2max) immediately. Accordingly, we assessed muscular blood flow distribution (ml/min/g, radioactive microspheres, 15 +/- 5 micron) among and within working muscle, VO2max, and arterial lactate in a rat preparation of myocardial infarction and heart failure (infarct size 36.0 +/- 3.3% of the left ventricle, n = 9), and in sham-operated animals (n = 11). Data were obtained at maximal treadmill exercise during alternate infusions of milrinone and saline. Total skeletal muscle blood flow during exercise was significantly lower in the infarction group (p less than .05 vs sham); reduced blood flow was primarily attributed to decreased flow to oxidative working muscle such as soleus and the red portion of gastrocnemius, whereas blood flow to glycolytic muscle portions (e.g., gastrocnemius white, vastus lateralis white) was similar in the infarction and sham-operated groups. Milrinone increased flow to the glycolytic working muscle portions in sham-operated animals (e.g., vastus lateralis white, 0.23 vs 0.29, p less than .05); by contrast, blood flow to the oxidative muscle fibers was increased in the infarction group (e.g., gastrocnemius red, 1.45 vs 1.87, p less than .05). Arterial lactate levels at similar workloads during exercise were higher in the infarction group (p less than .05). Neither lactate nor VO2max were significantly altered with milrinone in either group.(ABSTRACT TRUNCATED AT 250 WORDS)