Onset of blood lactate accumulation exercise capacity, skeletal muscle fibers and metabolism before and after coronary artery bypass grafting

Abstract

Male patients with effort angina were studied before (n = 7), 1 week, and 1 and 6 months (n = 6) after coronary artery bypass grafting (CABG) with 2 to 7 grafts. The test battery included graded exercise, which was performed until unbearable leg exertion or chest pain, or both, was present. Onsets of blood lactate accumulation, anginal pain, leg exertion and dyspnea were interpolated for either the lactate concentration 2 mmol X 1-1 or the ratings 2 on the Borg subjective intensity scale. Onsets of blood lactate accumulation and symptom-limited exercise capacity before surgery amounted to 58 and 100 W, respectively. The corresponding figures 6 months later were the same for onset of blood lactate accumulation, whereas symptom-limited exercise capacity had increased by 58%. Blood lactate was the same at rest and mild exercise (congruent to onset of blood lactate accumulation) but more than doubled at symptom-limited exercise capacity (peak blood lactate concentration). Muscle fiber typing showed a low figure for the slow twitch fiber proportion (35%), which was unchanged after 6 months. Fast twitch subtype C was elevated before (7%) but disappeared after surgery, and fast twitch subtype A percent increased correspondingly. The major muscle biochemical changes were in the glycogenolytic pathway and the lactate dehydrogenase enzyme system, which appeared to increase in a quantitative manner, but with an unchanged relative lactate dehydrogenase isozyme pattern. The increased symptom-limited exercise capacity was related to the increased glycogenolytic activity and peak blood lactate (i.e., increased "anaerobic power"). Whether the causative explanation was the relief from chest pain, i.e., a psychophysiologic feature or the biochemical changes that took place in the muscle could only be speculated on.