Author(s): BUYS, P., WESTON, M.E., CURTIN, E.L., GILDEA, N., EGAÑA, M., Institution: TRINITY COLLEGE DUBLIN, Country: IRELAND, Abstract-ID: 2537

INTRODUCTION:
Background Aerobic exercise training is known to induce beneficial adaptations in cerebrovascular reactivity (CVR), a key indicator of cerebrovascular health, but the acute response to exercise remains understudied. This is particularly relevant in inactive middle-aged adults, where cerebrovascular regulation may already be compromised. Moreover, the time course and kinetic response of CVR to acute aerobic exercise remain uncharacterised and may provide insight into longer-term adaptations. Therefore, this study examined the acute effects of moderate-intensity continuous training (MICT) and two high-intensity interval training (HIIT) protocols on: 1) hypercapnic CVR, 2) hypocapnic CVR, and 3) kinetic MCAv responses to hypercapnia.
METHODS:
Methods Seventeen inactive middle-aged adults (10 males, 47.2±8.9 years, V̇O2max 29.2±5.7 ml/kg/min) completed one preliminary and four experimental visits. During the preliminary visit, participants performed a ramp incremental cycle test to exhaustion to determine the gas exchange threshold (GET) and maximal oxygen uptake (V̇O2max), which was verified by a supramaximal test. Participants then completed four time-matched (30 min) experimental conditions on separate days in a counterbalanced order: seated control (CON), MICT performed at 90% GET, and two HIIT conditions [(10x1 min intervals at 70%Δ (HIIE10) or 4x4 min intervals at 20%Δ (HIIT4)], where Δ represents the difference between GET and V̇O2max. Middle cerebral artery blood velocity (MCAv) and end-tidal CO2 (PETCO2) were continuously measured using transcranial doppler ultrasound and a gas analyser. All CVR measures were assessed before, 10 and 60 min following each condition. Hypercapnic CVR was expressed as the absolute change in MCAv per mmHg change in PETCO₂ during 4 min of 6% CO₂ inhalation. Hypocapnic CVR was assessed during 1 min of voluntary hyperventilation performed at 25 breaths.min-1, with MCAv and PETCO₂ changes calculated from the final 10 s. The kinetic response of MCAv to hypercapnia was analysed using a novel mono-exponential model. Two-way repeated-measures ANOVA tested effects of condition and time on CVR, MCAv, PETCO₂, and kinetic parameters
RESULTS:
Results Baseline PETCO₂ was lower at 10 min vs pre- and 60 min in HIIT10 (Both P≤0.016) and HIIT4 (Both P≤0.021), and lower at 10 min vs CON in all exercise trials (all P≤0.042). Baseline MCAv remained unchanged across all trials (all P≥0.121). CVR to hypercapnia (all P>0.122) and hypocapnia (all P>0.296) was unchanged following all conditions. Kinetic analysis revealed no significant interaction effect for MCAv time delay (P=0.428), time constant (P=0.834) and amplitude (P=0.218).
CONCLUSION:
Conclusion. These novel findings indicate that CVR remains stable in the acute post-exercise period in inactive middle-aged adults. Furthermore, the absence of change in MCAv kinetics to hypercapnic stimuli after moderate- and high-intensity exercise, offers new insight into the temporal stability of CVR following acute exercise.