The Oxy- and Deoxy-Hb signals of the NIRS reflect the relative concentrations of oxygenated and deoxygenated hemoglobin in red blood cells in arterioles, capillaries, and venules within the illuminated area. The Oxy-Hb concen- tration is dependent on a balance between oxygen supply and demand in the regional area. Oxygen supply predom- inantly depends on regional blood flow. If oxygen supply is increased without changing oxygen demand, the Oxy-Hb signal is increased. If oxygen demand is increased without increasing oxygen supply, the Oxy-Hb signal is decreased. Fox and Raichle [27] reported that increased regional blood flow in association with brain neural activity exceeded oxygen metabolic demand. Hoshi et al. [28] demonstrated using a perfused rat brain model that increasing total cerebral blood flow causes an increase in regional Oxy-Hb and a decrease in Deoxy-Hb, while neural activity aug- mented by pentylenetetrazole accompanies an increase in regional Oxy-Hb and small changes in Deoxy-Hb. Taken together, the changes in Oxy-Hb are considered to be a more sensitive indicator of the changes in regional cerebral blood flow than the changes in Deoxy-Hb, while the
changes in Deoxy-Hb are determined more by venous oxygenation and blood volume than blood flow [28].
In this study, the prefrontal Oxy-Hb decreased or unchanged until 5 min from the onset of exercise and gradually increased in proportion to the exercise intensity until the end of dynamic exercise (Fig. 2), in agreement with the previous results [17, 18]. Since the Deoxy-Hb was unchanged throughout exercise except in the initial period, the signal of Oxy-Hb is considered to reflect regional cerebral blood flow in the prefrontal cortex [28–30]. It is known that changes in the Oxy-Hb are positively correlated with the changes in blood flow velocity of the middle cerebral artery [17, 18, 31]. MAP increased by 8–16 mmHg during dynamic exercise (Table 1). The small rises in perfusion pressure may have little influence on the prefrontal cerebral blood flow, because the increased MAP during exercise was within the range of cerebral autoreg- ulation [32]. Instead, it is conceivable that the change in regional cerebral blood flow follows an increase in neural activity of the prefrontal cortex, which may in turn cause improvement of cognitive function.
The Oxy- and Deoxy-Hb signals of the NIRS reflect the relative concentrations of oxygenated and deoxygenated hemoglobin in red blood cells in arterioles, capillaries, and venules within the illuminated area. The Oxy-Hb concen- tration is dependent on a balance between oxygen supply and demand in the regional area. Oxygen supply predom- inantly depends on regional blood flow. If oxygen supply is increased without changing oxygen demand, the Oxy-Hb signal is increased. If oxygen demand is increased without increasing oxygen supply, the Oxy-Hb signal is decreased. Fox and Raichle [27] reported that increased regional blood flow in association with brain neural activity exceeded oxygen metabolic demand. Hoshi et al. [28] demonstrated using a perfused rat brain model that increasing total cerebral blood flow causes an increase in regional Oxy-Hb and a decrease in Deoxy-Hb, while neural activity aug- mented by pentylenetetrazole accompanies an increase in regional Oxy-Hb and small changes in Deoxy-Hb. Taken together, the changes in Oxy-Hb are considered to be a more sensitive indicator of the changes in regional cerebral blood flow than the changes in Deoxy-Hb, while the
changes in Deoxy-Hb are determined more by venous oxygenation and blood volume than blood flow [28].
In this study, the prefrontal Oxy-Hb decreased or unchanged until 5 min from the onset of exercise and gradually increased in proportion to the exercise intensity until the end of dynamic exercise (Fig. 2), in agreement with the previous results [17, 18]. Since the Deoxy-Hb was unchanged throughout exercise except in the initial period, the signal of Oxy-Hb is considered to reflect regional cerebral blood flow in the prefrontal cortex [28–30]. It is known that changes in the Oxy-Hb are positively correlated with the changes in blood flow velocity of the middle cerebral artery [17, 18, 31]. MAP increased by 8–16 mmHg during dynamic exercise (Table 1). The small rises in perfusion pressure may have little influence on the prefrontal cerebral blood flow, because the increased MAP during exercise was within the range of cerebral autoreg- ulation [32]. Instead, it is conceivable that the change in regional cerebral blood flow follows an increase in neural activity of the prefrontal cortex, which may in turn cause improvement of cognitive function.
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