Relationship Between Ventilatory Threshold and Cerebral Blood Flow During Maximal Exercise in Humans

Background: This work studied the relationship between changes in cerebral blood flow velocity (CBFV) through the middle cerebral artery (MCA) with non-invasive ventilatory threshold (VT) measurements determined by gasexchange during upright maximal cycle ergometry. Methods: Fourteen (M=8, F=6) healthy, young (23.1 ± 3.9 yr) participants volunteered for this study and performed a cycle ergometer protocol to maximal exertion. The CBFV was monitored continuously through the MCA by transcranial Doppler ultrasound and was assessed at rest, VT, and at maximal exertion (VO2max). Ventilatory threshold was assessed using three common methods: 1) V-slope, 2) nadir of the ventilatory equivalent for carbon dioxide production (VE/VCO2), and 3) maximal partial pressure of carbon dioxide (PETCO2). Results: Analysis of variance demonstrated significant (p<0.001) main effects for CBFV, volume of oxygen consumed (VO2), volume of carbon dioxide produced (VCO2), and PETCO2. Bonferroni post hoc analysis demonstrated an increase in CBFV from rest to a peak CBFV (p<0.01) with a decrease from peak CBFV to VO2max (p<0.01). Stepwise linear regression suggest the only predictor of a reduction in CBFV during maximal exercise is the nadir of VE/VCO2 (p<0.01). Conclusion: These data demonstrate an increase in CBFV during dynamic upright exercise up to approximately 78% VO2max after which CBFV decreases significantly to VO2max. This decrease in CBFV was closely related to common non-invasive measures of ventilatory threshold suggesting a close relationship between cerebral blood flow and the threshold for ventilatory compensation.