Objective: This investigation tested the hypothesis that the dynamics of muscle microvascular O-2 pressure (PO(2)m, which reflects the ratio of O-2 utilization [VO2] to O-2 delivery [QO(2)]) following the onset of contractions would be altered in chronic heart failure (CHF). Methods: Female Sprague-Dawley rats were subjected to a myocardial infarction (MI) or a sham operation (Sham). Six to 10 weeks post Sham (n=6) or MI (n=17), phosphorescence quenching techniques were utilized to determine PO,m dynamics at the onset of spinotrapezius muscle contractions ( 1 Hz). Results: MI rats were separated into groups with Moderate (n = 10) and Severe (n 7) CHF based upon the degree of left ventricular (LV) dysfunction as indicated by structural abnormalities (increased right ventricle weight and lung weight normalized to body weight). LV end-diastolic pressure was elevated significantly in both CHF groups compared with Sham (Sham, 3+/-1; Moderate CHF, 9+/-2; Severe CHF, 27+/-4 mmHg, P<0.05). The PO(2)m response was modeled using time delay and exponential components to fit the PO(2)m response to the steady-state. Compared with Shams, the time constant (tau) of the primary PO(2)m response was significantly speeded in Moderate CLIF (tau, Sham, 19.0+/-1.5; Moderate CHF, 13.2+/-1.9 s, P<0.05) and slowed in Severe CHF (tau, 28.2+/-3.4 s, P<0.05). Within the Severe CHF group, tau increased linearly with the product of right ventricular and lung weight (r=0.83, P<0.05). Conclusions: These results suggest that CHF alters the dynamic matching of muscle VO2-to-QO(2) across the transition from rest to contractions and that the nature of that perturbation is dependent upon the severity of cardiac dysfunction. (C) 2002 Elsevier Science B.V. All rights reserved.
