Author(s): HIURA, M., SHIBUTANI, H., FUNAKI, A., Institution: AOMORI UNIVERSITY, Country: JAPAN, Abstract-ID: 2196

INTRODUCTION:
There has not been confirmed if cerebral blood flow (CBF) in the prefrontal cortex (PFC) would change during exercise according to studies using positron emission tomography (PET). Despite uncertainly, huge number of studies explored cerebral oxygenation in PFC using near-infrared spectroscopy (NIRS) to identify the role of PFC in terms of executive function and affective responses induced by exercise. Since our previous studies using time domain functional NIRS (TD-fNIRS) demonstrated that in PFC cerebral blood volume (CBV) stayed at the same level as the end of moderate-intensity continuous exercise for two minutes after the cessation, we predict that CBF may also increase. The aim of this study is to explore if intensity and duration of exercise affect changes in in CBV both during and after a bout of exercise.
METHODS:
Fourteen active healthy males (age, 21 ± 1 years; height, 176 ± 7 cm, weight, 71± 10 kg; maximal oxygen consumption [VO2max], 46.8 ± 8.3 mL min-1 kg-1) participated. While all participants performed cycling exercise for 15 min at 60%VO2max (ExM), seven persons performed both ExM and cycling exercise for 4 min at 80%VO2max (ExV). Cardiovascular and respiratory parameters and CBV were measured. TD-fNIRS was used to measure cerebral hemoglobin oxygen saturation (ScO2) and total hemoglobin concentration (HbT), a surrogate of CBV, in both sides of PFC. During ExH and ExV, ratings of perceived exertion (RPE) were monitored.
RESULTS:
At the end of exercise end-tidal CO2 (PETCO2) increased from rest both in ExM and ExV. RPE at the end was higher in ExV compared with ExM, 14.3 ± 1.4 and 13.1 ± 1.3 (p=0.03). For HbT, there was no interaction effect (module x time, p=0.17, F=1.52). In ExM, HbT increased in the left and right PFC compared with rest from 84.3 ± 9.3 to 94.2 ± 11.7 and from 78.4 ± 19.0 to 86.5 ± 20.1 μmol /L at the end of exercise (p=0.002 and 0.01) and increased to 91.5 ± 9.9 and to 85.9 ± 21.0 μmol /L at 3 min from the cessation of exercise (p= 0.006 and 0.004). In ExV, HbT did not increase at the end of exercise, from 91.6 ± 9.3 to 94.9 ± 11.4 and from 83.2 ± 15.4 to 86.0 ± 17.2 μmol /L in both PFC (p= 0.08 and 0.22) but increased to 95.2 ± 9.5 and 87.5 ± 15.0 μmol /L at 3 min from the cessation of exercise (p= 0.02). ScO2 remained throughout the course.
CONCLUSION:
While cardiovascular variables returned to near the resting status within two minutes after the cessation of exercise, CBV remained higher than rest for three minutes both in ExM and ExV. As we hypothesized, CBV differed by intensity and duration of exercise. Although CBF cannot be identified only by fNIRS, increases in CBV may be consistent with those in CBF. By dual measurements with TD-fNIRS and PET during exercise, the relationship between CBV and CBF during exercise could be identified and oxygen metabolism in PFC could be calculated with given CBF. This study adds useful information to the protocol of these dual measurements regarding the situation after the cessation of exercise.