Does the regional oxygen uptake measured by near infrared spectroscopy reflect the phase II pulmonary oxygen uptake at the onset of exercise?
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+/-2.159 s, on-VT: 7.760+/-2.035 s, above-VT: 9.532+/-2.342 s) were significantly faster than the time constants of pVO(2) (pVO(2)-Tc: below-VT: 23.8+/-4.4 s, on-VT: 25.9+/-5.1 s, above-VT: 26.3+/-5.7 s) (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.
Shibuya
Ken-ichi
K
Graduate School of Human-Environment Studies, Kyushu University, Kasuga City, Fukuoka, Japan. SHIBUYA_ken-ichi@ihs.kyushu-u.ac.jp
Maruyama
Atsuo
A
Hirakoba
Kohji
K
Maeda
Masato
M
Ogaki
Tetsuro
T
D000328:Adult; D001642:Bicycling / Q000502:physiology; D015444:Exercise / Q000502:physiology*; D006801:Humans; D007700:Kinetics; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology; D010100:Oxygen / Q000493:pharmacokinetics*; D010101:Oxygen Consumption; D012680:Sensitivity and Specificity; D019265:Spectroscopy, Near-Infrared
D010100:Oxygen