Validation of a continuous-wave, single-distance NIRS oxymeter for the determination of muscle oxygenation during cycling.

Validation of a continuous-wave, single-distance NIRS oxymeter for the determination of muscle oxygenation during cycling. Silvia Pogliaghi1, Lorenzo Casiello1, Andrea Bandera2 1 Faculty of Kinesiology, University of Verona, Italy; 2 Nirox srl, Brescia, Italy An Italian company recently developed a relatively inexpensive continuous-wave (CW), single-distance near-infrared spectroscopy (NIRS) oxymeter that allows the calculation of absolute values of deoxygenated haemoglobin (deoxyHb). This absolute quantification is made possible by an in-vivo estimate of the scattering coefficient (based on direct measures of the scattering at the water absorption peak and on its linear extrapolation to the near-infrared range). The calculated scattering coefficient is assumed not to change over the time of the experiment. PURPOSE: We tested the possible correspondence between non-invasive measures of muscle deoxyHb obtained using this CW device and a frequency-domain (FD) multi-distance NIRS system, used as a reference method. METHODS: 11 healthy sedentary males (27±5 years, 176±1 cm , 73±8 kg, 54±4 ml*kg-1*min-1 VO2max) performed an incremental cycling test. Following a 3-min rest, subjects pedaled at 50 watt for 3 min. Thereafter, the workload was increased stepwise, 20 watt per minute, up to voluntary exhaustion. During the tests, muscle deoxyHb was monitored continuously on the vastus lateralis of the right leg, using the reference FD device (FDdeoxyHb), and on the right leg, using the CW instrument (CWdeoxyHb). The average values of the last 30s of rest and warm-up cycling, and the last 10 s of each stage were used for statistical analysis. Agreement between the two instruments was tested by Bland Altman analysis (significance ≤0.05). RESULTS: Resting CWdeoxyHb and FDdeoxyHb were 27±6 and 29±5 mmol*l-1 respectively (not different). As expected, deoxyHb increased as a function of exercise intensity reaching 43±9 (CWdeoxyHb) and 44±10 mmol*l-1 (FDdeoxyHb) upon exhaustion (not different). At all exercise intensities, CWdeoxyHb was not significantly different from FDdeoxyHb (bias 0.93, not different from 0; precision 7.6 mmol*l-1). CONCLUSIONS: The main finding of this study is that there is a very good agreement between muscle deoxyHb values measured by the evaluated CW device and the reference FD oxymeter. Compared to the reference device, the new, relatively inexpensive oxymeter yields unbiased and precise deoxyHb values during incremental cycling exercises in healthy sedentary males. The study was supported by Nirox srl, Italy