Effects of chronic heart failure on microvascular oxygen exchange dynamics in muscles of contrasting fiber type

In rat spinotrapezius muscle, chronic heart failure (CHF) speeds microvascular O-2 pressure (pO(2); index Of O-2 delivery-to-O-2 uptake) dynamics across the rest-contractions transition [Cardiovasc. Res. 56 (2002) 479]. Due to the mosaic nature of this muscle, the effect of CHF on microvascular pO(2), dynamics in different fiber types remains unclear. Objective: Based upon derangements of endothelial function and blood flow responses, we hypothesized that CHF would speed microvascular pO(2) dynamics (reduced O-2 delivery-to-O-2 uptake ratio) in type I muscle (soleus, similar to 84% type I), but not in type II muscle (peroneal, similar to 86% type II [J. Appl. Physiol. 80 (1996) 261]). Methods: Using phosphorescence quenching, microvascular pO(2) was measured at rest and across the rest-contractions transition (1 Hz) in soleus and peroneal of non-infarcted control (control; n = 7), and Sprague-Dawley rats with moderate (moderate; elevated left ventricular end-diastolic pressure (LVEDP) 10 +/- 2 mm Hg, n = 10) and severe (severe; LVEDP 28 +/- 4 mm Hg; n = 5) CHF. Results: The microvascular pO(2) mean response time (time delay + time constant) was progressively speeded with increasing severity of CHF in soleus (control, 38.7 +/- 2.0; moderate, 29.1 +/- 1.5; severe, 22.5 +/- 3.9 s; P less than or equal to 0.05), but not in peroneal (control = moderate = severe). Conclusion: As type I fibers are recruited predominately for moderate intensity exercise, the more rapid lowering of soleus microvascular pO(2) in CHF would reduce the blood-muscle O-2 driving gradient, exacerbate phosphocreatine and glycogen breakdown, and provide a mechanism for slowed O-2 uptake kinetics and premature fatigue in CHF. (C) 2003 European Society of Cardiology. Published by Elsevier B.V. All rights reserved.