© 2004 by European Society of Cardiology
Copyright © 2004, European Society of Cardiology
Effects of chronic heart failure on microvascular oxygen exchange dynamics in muscles of contrasting fiber type
aDepartments of Health and Kinesiology, and Medical Physiology, Texas A&M University, College Station, TX, USA
bDepartments of Anatomy and Physiology, and Kinesiology, Kansas State University, 228 Coles Hall, Manhattan, KS 66506-5802, USA
* Corresponding author. Tel.: +1-785-532-4523; fax: +1-785-532-4557. musch{at}vet.ksu.edu
In rat spinotrapezius muscle, chronic heart failure (CHF) speeds microvascular O2 pressure (pO2; index of O2 delivery-to-O2 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 pO2 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 pO2 dynamics (reduced O2 delivery-to-O2 uptake ratio) in type I muscle (soleus, 
84% type I), but not in type II muscle (peroneal, 86% type II [J. Appl. Physiol. 80 (1996) 261]). Methods: Using phosphorescence quenching, microvascular pO2 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 pO2 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
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 pO2 in CHF would reduce the blood-muscle O2 driving gradient, exacerbate phosphocreatine and glycogen breakdown, and provide a mechanism for slowed O2 uptake kinetics and premature fatigue in CHF.
KEYWORDS Phosphorescence quenching; Oxygen exchange; Soleus; Peroneal
Abbreviations: CHF, chronic heart failure • pO2, partial pressure of oxygen • Control, non-infarcted rats • Moderate, rats with moderate levels of CHF • Severe, rats with severe levels of CHF • LVEDP, left ventricle end-diastolic pressure • RV, right ventricle • MRT, mean response time (time delay+time constant) • T63, time to 63% of final response • TD, time delay • 
, time constant • krpO2, rate constant of pO2 change (
pO2/) • pO2, change in microvascular pO2 from non-contracting values to nadir