Test-retest reliability of skeletal muscle oxygenation measurements during submaximal cycling exercise in patients with chronic heart failure.

The potential purpose of near-infrared spectroscopy (NIRS) as a clinical application in patients with chronic heart failure (CHF) is the identification of limitations in O-2 delivery or utilization during exercise. The objective of this study was to evaluate absolute and relative test-retest reliability of skeletal muscle oxygenation measurements in patients with CHF. Thirty patients with systolic heart failure (left ventricular ejection fraction 31 +/- 8%) performed 6-min constant-load cycling tests at 80% of the anaerobic threshold (AT) with tissue saturation index (TSI) measurement at the vastus lateralis. Tests were repeated after 10 +/- 5days to evaluate reliability. Absolute reliability was assessed with limits of agreement (LoA, expressed as bias +/- random error) and coefficients of variation (CV) for absolute values (LoA range: 04 +/- 62% to 06 +/- 79%; CV range: 47-71%), amplitudes (LoA range -05 +/- 58% to -07 +/- 68%; CV range: 262-421%), onset and recovery kinetics (mean response times; LoA 04 +/- 95s, CV 235% and LoA -58 +/- 508s, CV 674% respectively) and overshoot characteristics (CV range 457-2086%). Relative reliability was assessed with intraclass correlation coefficients for absolute values (range 074-090), amplitudes (range 085-092), onset and recovery kinetics (053 and 051, respectively) and overshoot characteristics (range 017-074). In conclusion, absolute reliability of absolute values and onset kinetics seems acceptable for serial within-subject comparison, and as such, for evaluation of treatment effects. Absolute reliability of amplitudes and recovery kinetics is considered unsatisfactory. Relative reliability of absolute values and amplitudes is sufficient for purposes of physiological distinction between patients with CHF. Despite lower relative reliability, kinetics may still be useful for clinical application.