Does the Regional Oxygen Uptake Measured by Near Infrared Spectroscopy Reflect the Phase II Pulmonary Oxygen Uptake at the Onset of Exercise?

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It has been hypothesized that the signals of near infrared spectroscopy (NIRS) would reflect muscle O_2 uptake (mVO_2). Although it is not definite that NIRS signals accurately reflect mVO_2, there is every possibility that NIRS signals at least reflect regional O_2 uptake (rVO_2). The phase II kinetics of pulmonary oxygen uptake (pVO_2) is regarded as reflecting mVO_2 at the onset of exercise. To examine whether the rVO_2 on-kinetics measured by NIRS reflects the mVO_2 on-kinetics at the onset of exercise, we compared the rVO_2 as measured by NIRS with the phase II kinetics of pVO_2 at the onset of exercise. Twelve healthy male subjects cycled a Monark ergometer at three different intensities: below the ventilatory threshold (VT) level (below-VT), on the VT level (on-VT), and above the VT level (above-VT), for 6 minutes on three separate occasions. The rVO_2 was calculated from the concentration of oxyhemoglobin and deoxyhemoglobin, as measured by NIRS every 3 seconds. The pVO_2 was determined by the breath-by-breath method. A significant relationship between the amount of increases of pVO_2 and rVO_2 from rest to the end of exercise among all levels of exercise intensity was found (r=0.935, P<0.001). The time constants of rVO_2 (rVO_2-Tc: below-VT: 6.514±2.159s, on-VT: 7.760±2.035s, above-VT: 9.532±2.342s) were significantly faster than the time constants of pVO_2 (pVO_2-Tc: below-VT: 23.8±4.4s, on-VT: 25.9±5.1s, above-VT: 26.3±5.7s) (P<0.001). There was no significant relationship between rVO_2-Tc and pVO_2-Tc for each intensity (P>0.05). We conclude that the rVO_2 on-kinetics measured by NIRS does not necessarily reflect the mVO_2 kinetics at the onset of exercise.

Does the Regional Oxygen Uptake Measured by Near Infrared Spectroscopy Reflect the Phase II Pulmonary Oxygen Uptake at the Onset of Exercise?

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