Uncoupling Between Cerebral Perfusion And Oxidative Metabolism In The Prefrontal Cortex Evoked By Moderate-intensity Exercise

Regional and activation-dependent differences in the relationship between cerebral blood flow (CBF) and cerebral metabolic rate for oxygen (CMRO2) were postulated by studies using positron emission tomography (PET). To clarify this relationship during exercise, near-infrared spectroscopy (NIRS) that detects oxygenation supplements PET measurements. PURPOSE: To estimate the relationships between cerebral perfusion and oxidative metabolism in the PFC during exercise performed at different intensities using data observed in PET and NIRS studies. METHODS: For each PET and NIRS study, 12 recreationally active men with identical characteristics (age, 24 ± 6 years) were enrolled. They performed a dual-intensity cycling exercise, 17-min of low-intensity (ExL) followed by 3-min of moderate-intensity (ExM). Exercise intensities for ExL and ExM were determined as 30% and 45% of the participants’ heart rate reserve, respectively. Cardiovascular, respiratory parameters and the rate of perceived exertion (RPE) were measured. In the PFC, CBF was measured using PET during ExL while cerebral oxygenation was measured during both ExL and ExM by near-infrared time-resolved spectroscopy (TRS) that indicates absolute values of cerebral hemoglobin oxygen saturation (ScO2) and total hemoglobin concentration ([HbT]) that was converted to cerebral blood volume (CBV). We calculated the relative changes from the baseline in CBV (rCBV) and CMRO2 (rCMRO2), assuming a constant power law relationship between CBF and CBV. Comparisons for rCMRO2 and rCBV were made using two-way ANOVA with repeated measures. RESULTS: At ExL, CBF and [HbT] did not change from the rest. When ExL changed to ExM, pulmonary oxygen uptake (VO2) increased from 34 ± 5 to 47 ± 3 % of peak VO2 and RPE increased from 8.8 ± 1.1 to 11.4 ± 1.7 (a.u.) (p < 0.001). [HbT] increased from 72.0 ± 13.0 to 73.8 ± 13.8 μM (p < 0.05), while ScO2 remained. rCMRO2 and rCBV increased from 1.04 ± 0.04 to 1.18 ± 0.17 and from 1.00 ± 0.02 to 1.07 ± 0.05, respectively, and rCMRO2 was greater than rCBV at ExM (p < 0.05). CONCLUSIONS: Alteration in the relationship between cerebral perfusion and oxidative metabolism in the PFC was attributable to exercise intensity. Further investigations for CBF and CMRO2 by simultaneous PET and TRS measurements will clarify this uncoupling phenomenon more accurately.