Effects of chronic heart failure on skeletal muscle capillary hemodynamics at rest and during contractions

Chronic heart failure (CHF) reduces muscle blood flow at rest and during exercise and impairs muscle function. Using intravital microscopy techniques, we tested the hypothesis that the speed and amplitude of the capillary red blood cell (RBC) velocity (V-RBC) and flux (F-RBC) response to contractions would be reduced in CHF compared with control (C) spinotrapezius muscle. The proportion of capillaries supporting continuous RBC flow was less (P < 0.05) in CHF (0.66 +/- 0.04) compared with C (0.84 +/- 0.01) muscle at rest and was not significantly altered with contractions. At rest, V-RBC (C, 270 +/- 62; CHF, 179 +/- 14 mu m/s) and F-RBC (C, 22.4 +/- 5.5 vs. CHF, 15.2 +/- 1.2 RBCs/s) were reduced (both P < 0.05) in CHF vs. C muscle. Contractions significantly (both P < 0.05) elevated V-RBC (C, 428 +/- 47 vs. CHF, 222 +/- 15 mu m/s) and F-RBC (C, 44.3 +/- 5.5 vs. CHF, 24.0 +/- 1.2 RBCs/s) in C and CHF muscle; however, both remained significantly lower in CHF than C. The time to 50% of the final response was slowed (both P < 0.05) in CHF compared with C for both V-RBC (C, 8 +/- 4; CHF, 56 +/- 11 s) and F-RBC (C, 11 +/- 3; CHF, 65 +/- 11 s). Capillary hematocrit increased with contractions in C and CHF muscle but was not different (P > 0.05) between CHF and C. Thus CHF impairs diffusive and conductive O-2 delivery across the rest-to-contractions transition in rat skeletal muscle, which may help explain the slowed O2 uptake on-kinetics manifested in CHF patients at exercise onset.