Kinetics of cerebral blood flow in the moderate and heavy exercise intensity domains estimated using the transcranial Doppler method

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Purpose: The purpose of this study was to investigate the kinetics of cerebral blood flow (CBF) in conjunction with cardiopulmonary response during constant-work rate cycling exercise of moderate and heavy intensities. Methods: Seven subjects (6 males and 1 female; age, 25.4 ± 7.7 yr; height, 171.9 ± 4.3 cm; body mass, 67.7 ± 11.4 kg) participated in the present study. The subjects completed incremental cycle ergometer test to assess VO2peak, the gas exchange threshold (GET), and the respiratory compensation threshold (RCT). Secondary, the subjects performed two sets of constant workload of exercise bouts (10 min) by cycle ergometer corresponding to the level of 10% below GET (moderate intensity) and RCT (heavy intensity). Respiratory gas analysis and the middle cerebral blood flow mean velocity (MCA Vmean) were measured simultaneously using the transcranial Doppler (TCD) method. PaCO2 was estimated (ePaCO2) using PETCO2 and VT. We assumed that MCA Vmean could be used as an index of the global CBF. Results: VO2 and ePaCO2 remained stable after the onset at moderate intensity whereas VO2 increased throughout the trail and ePaCO2 decreased after the onset at heavy intensity. The percentage change from baseline for MCA Vmean (ΔMCA Vmean) increased within 2 min to a peak value within 2 min by 32.8 ± 9.1% and 31.8 ± 11.8% at moderate and heavy intensity, respectively. In the heavy-intensity exercise ΔMCA Vmean decreased further below the response to moderate exercise as time progressed prior to the recovery phase (trials × time: F = 3.84, P < 0.05). Conclusion: The different kinetics of MCA Vmean between moderate and heavy-intensity exercise was identified during a constant work rate cycling exercise. We found that in heavy-intensity trials, the relationship between ePaCO2 and MCA Vmean was different to that at moderate intensity during the recovery phase.

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