Abstract
The sigmoid profile of muscle deoxygenation during ramp-incremental exercise (RI) has been suggested to reflect the conflation of: 1) the fast kinetics of muscle blood flow (Q) relative to muscle O2 consumption (VO2) at low work rates (WR); and 2) the attenuation of O2 extraction as WR increases. The positioning of this sigmoid (within the relative or absolute WR domain) during RI is right-shifted in trained cyclists, suggesting a better maintenance of Q/VO2 in comparison to controls. Thus, a left-shifted deoxygenation profile in chronic heart failure (CHF) where Q kinetics are slow is suggested (Ferreira et al. J Appl Physiol 103:1999-, 2007). PURPOSE: To determine whether a kinetic mismatch of Q/VO2 during RI contributes to a leftward shift in locomotor muscle deoxygenation dynamics in CHF. METHODS: Sixteen CHF patients (NYHA class II-III) completed symptom-limited RI cycle ergometry (4-12 W.min-1) and 6 min of moderate (M; 90% lactate threshold, LT) and heavy (H; just above LT) intensity constant WR exercise. Healthy participants (n = 16; 23 ± 3 yr) completed RI at 25 W.min-1. Vastus lateralis oxygenation was measured by near-infrared spectroscopy (NIRO 200, Hamamatsu, Japan) and pulmonary VO2 by a mass spectrometer and turbine (MSX, NSpire, UK). The tissue oxygenation index (TOI) was normalized to ramp duration and amplitude, and characterized by y=A0+A/(1+e-(-c+dx)), where c/d is the %WRpeak at (A0+A)/2. RESULTS: Five CHF patients exhibited a linear, or accelerating, fall in TOI. In the remaining 11, the TOI profile was sigmoid and c/d was similar to healthy participants (54 ± 18 vs 51 ± 12 %WRpeak; p > 0.05). In CHF, steady-state TOI in M (54 ± 9 %) and H (49 ± 10 %) were not different (p > 0.05) from TOI at the appropriate WR in RI (M: 54 ± 10; H: 50 ± 12 %). CONCLUSIONS: The normalized c/d of TOI in RI was similar between CHF and healthy participants and not left-shifted as proposed under conditions of slow Q kinetics. The absence of a sigmoid TOI in 5 patients was not related to disease severity, etiology or VO2max. The sigmoid profile of muscle deoxygenation in RI does not appear to reflect kinetic dissociation of Q and VO2. Rather the sequential recruitment of muscle fibers and/or differences in Q/VO2 slope and intercept between fiber types is implicated in mediating this response. Supported by The British Council (RC20)
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