Author(s): WESTON, M., BUYS, P., CURTIN, E., WILLIAMSON, W., BILLINGER, S.A., POOLE, D.C., O’SHEA, D., SILKE, A., DIVILLY, P., GILDEA, N., EGANA, M. , Institution: TRINITY COLLEGE DUBLIN, Country: IRELAND, Abstract-ID: 2661

INTRODUCTION:
Individuals living with Type 2 diabetes mellitus (T2D) have reduced exercise tolerance and impairments in peripheral and cerebral vascular function. Increases in middle cerebral artery blood velocity (MCAv) are blunted during intermittent incremental exercise in active males with T2D. However, whether this occurs in inactive men and women with T2D, and the underlying mechanisms, is unknown. Herein, this study: 1) compared the MCAv response during ramp exercise in inactive adults with T2D compared to non-T2D controls, and 2) explored relationships between MCAv and ventilatory exercise responses.
METHODS:
17 inactive adults with uncomplicated T2D (9 male) and 17 inactive healthy controls (CON) matched for sex, age (51.7±10.7 vs 51.6±9.5 y, P=0.99) and BMI (29.5±5.1 v 28.7±3.8 kg.m-2, P=0.61) participated in this study. Participants completed a ramp incremental cycle test to exhaustion, followed by supramaximal verification of maximal oxygen uptake (V̇O2max). MCAv was measured throughout by transcranial Doppler ultrasound, and end-tidal carbon dioxide (PETCO2) by a metabolic cart (Innocor, Innovision). Data were analysed during unloaded warm-up (baseline), at the gas exchange threshold (GET), respiratory compensation point (RCP) and exhaustion, and expressed in absolute terms and as relative change from baseline (Δ%). The V̇E/V̇CO2 slope was calculated using linear regression. Data were analysed using 2-way mixed model ANOVAs and Pearson correlation.
RESULTS:
V̇O2max was significantly lower in T2D compared to CON (25.1±4.7 vs 28.3±4.3 ml.kg-1.min-1, P=0.046), with no difference in the V̇E/V̇CO2 slope (P=0.50). Although baseline MCAv was not different between groups (P=0.72), there were effects of exercise intensity (P<0.001) and group (P=0.049) on Δ%MCAv. MCAv increased from baseline to GET in CON (+9.1±10.1%, P=0.001), but not T2D (+3.2±11.3%, P=0.23). Δ%MCAv was significantly lower at exhaustion compared to GET and RCP in both groups (all P<0.001), and fell below baseline at exhaustion in T2D (-11.3±15.2%, P=0.002), but not CON (-2.1±13.0%, P=0.55). Baseline PETCO2 did not differ between groups (P=0.07), and increased from baseline to GET in CON only (+6.9±8.7%, P<0.001, T2D: +2.9±5.4%, P=0.11), before falling below baseline at exhaustion in both groups (all P<0.001) Overall, Δ%MCAv correlated with Δ%PETCO2 and V̇E/V̇CO2 slope at GET (r=0.77, P<0.001, r=-0.45, P=0.007, respectively), RCP (r=0.81, P<0.001, r=-0.56, P<0.001) and exhaustion (r=0.71, P<0.001, r=-0.49, P=0.008), but not with V̇O2max (all r≤0.27, P≥0.12).
CONCLUSION:
These novel findings demonstrate that inactive adults living with T2D have a blunted MCAv response to incremental exercise. These impairments are closely associated with changes in PETCO2 and ventilatory efficiency (but not V̇O2max), potentially indicating altered CO2-mediated cerebrovascular regulation in T2D.