Differences in cerebrovascular regulation and ventilatory responses during ramp incremental cycling in children, adolescents and adults

Abstract

Regulation of cerebral blood flow during exercise in youth is poorly understood. This study investigated the cerebrovascular and ventilatory responses to a ramp incremental cycle test to exhaustion in 14 children (mean ± SD age: 9.4±0.9 y), 14 adolescents (12.4±0.4 y) and 19 adults (23.4±2.5 y). Middle cerebral artery blood velocity (MCAv), partial pressure of end-tidal CO2 (PETCO2) and ventilatory parameters were analysed at baseline, gas exchange threshold (GET), respiratory compensation point (RCP) and exhaustion. The increase in minute ventilation relative to CO2 production during exercise was also calculated (VE/VCO2 slope). Relative change from baseline (Δ%) in MCAv was lower in children, compared to adolescents and adults at GET (15±10% vs 26±14% and 24±10%, respectively, P≤0.03, effect size (d)=0.9) and RCP (13±11% vs 24±16% and 27±15%, respectively, P≤0.05, d≥0.8). Δ%MCAv was similar in adults and adolescents at all intensities, and similar in all groups at exhaustion. The magnitude of the V̇E/ V̇CO2 slope was negatively associated with Δ%MCAv at GET and RCP across all participants (P≤0.01, r=-0.37 to -0.48). Δ%PETCO2 was smaller in children and adolescents compared to adults at GET and RCP (P≤0.05, d≥0.6). In children, Δ%PETCO2 and Δ%MCAv were not associated from baseline-GET (r̄=0.14) and were moderately associated from RCP-exhaustion (r̄=0.49). These relationships strengthened with increasing age, and were stronger in adolescents (baseline-GET: r̄=0.47, RCP-exhaustion: r̄=0.62) and adults (baseline-GET: r̄=0.66, RCP-exhaustion: r̄=0.78). These findings provide the first evidence on the development of the regulatory role of PETCO2 on MCAv during exercise in children, adolescents and adults.