Effects of dynamic changes in arterial pressure and carbon dioxide on middle cerebral artery blood velocity during high-intensity interval exercise.

Cerebral autoregulation at rest is enhanced at lower arterial partial pressure of carbon dioxide ([Formula: see text]), and [Formula: see text] progressively decreases during high-intensity interval exercise (HIIE). Therefore, we investigated whether cerebrovascular control changes across a bout of HIIE. We hypothesized that cerebral autoregulation would improve during the later stages of HIIE when estimated [Formula: see text] (e[Formula: see text]) is reduced. Fourteen young healthy adults (5 women) performed 18.5 min of pseudorandom HIIE, where work rate alternated between 25 W and 50% of the difference between the ventilatory threshold and peak oxygen uptake. Autoregressive moving average (ARMA) analysis quantified indices of cerebral autoregulation and cerebrovascular reactivity to CO2 for the first and second halves of HIIE. Mean arterial pressure at the level of the middle cerebral artery (MAPMCA; 89 ± 9 vs. 83 ± 10 mmHg; P < 0.001), e[Formula: see text] (40.9 ± 2.9 vs. 38.4 ± 3.3 mmHg; P < 0.001), and mean middle cerebral artery blood velocity (MCAv; 61.1 ± 16.1 vs. 56.5 ± 15.8 cm·s-1; P < 0.001) were all higher during the first half of the test. ARMA analysis revealed lower (P = 0.004) steady-state changes in MCAv in response to a step increase in MAP in the second half of HIIE (0.15 ± 0.11 cm·s-1·mmHg-1) compared with the first half (0.23 ± 0.14 cm·s-1·mmHg-1), suggesting improved autoregulation in the later stages of HIIE when e[Formula: see text] was lower. Large transient increases in MCAv at the onset of high-intensity intervals were temporally linked to spikes in MAP, which were exacerbated by shorter recovery intervals. These results suggest a dynamic change in the regulation of cerebrovascular and systemic hemodynamics as a function of time and work rate pattern during HIIE.NEW & NOTEWORTHY Time-series analysis revealed changes in cerebrovascular regulation as a function of time during high-intensity interval exercise (HIIE), with cerebral autoregulation improving from early to late exercise when estimated [Formula: see text] was reduced. Furthermore, transient spikes in blood pressure at the onset of high-intensity intervals were exacerbated by shorter periods of active recovery between intervals, suggesting that different HIIE protocols may confer different risks of transmitting rapid and large increases in mean arterial pressure to the brain.