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Purpose: This study had 2 objectives: (1) to examine whether the validity of the supramaximal verification test for maximal oxygen uptake ( V ˙ O 2 max) differs in children and adolescents when stratified for sex, body mass, and cardiorespiratory fitness and (2) to assess sensitivity and specificity of primary and secondary objective criteria from the incremental test to verify V ˙ O 2 max. Methods: In total, 128 children and adolescents (76 male and 52 females; age: 9.3–17.4 y) performed a ramp-incremental test to exhaustion on a cycle ergometer followed by a supramaximal test to verify V ˙ O 2 max. Results: Supramaximal tests verified V ˙ O 2 max in 88% of participants. Group incremental test peak V ˙ O 2 was greater than the supramaximal test (2.27 [0.65] L·min−1 and 2.17 [0.63] L·min−1; P <.001), although both were correlated (r =.94; P <.001). No differences were found in V ˙ O 2 plateau attainment or supramaximal test verification between sex, body mass, or cardiorespiratory fitness groups (all Ps >.18). Supramaximal test time to exhaustion predicted supramaximal test V ˙ O 2 max verification (P =.04). Primary and secondary objective criteria had insufficient sensitivity (7.1%–24.1%) and specificity (50%–100%) to verify V ˙ O 2 max. Conclusion: The utility of supramaximal testing to verify V ˙ O 2 max is not affected by sex, body mass, or cardiorespiratory fitness status. Supramaximal testing should replace secondary objective criteria to verify V ˙ O 2 max. [ABSTRACT FROM AUTHOR]

The acute effect of exercise intensity on cerebrovascular reactivity and whether this mirrors changes in peripheral vascular function have not been investigated. The aim of this study was to explore the acute effect of exercise intensity on cerebrovascular reactivity (CVR) and peripheral vascular function in healthy young adults (n = 10, 6 females, 22.7 ± 3.5 yr). Participants completed four experimental conditions on separate days: high-intensity interval exercise (HIIE) with intervals performed at 75% maximal oxygen uptake (̇O2max; HIIE1), HIIE with intervals performed at 90% ̇O2max (HIIE2), continuous moderate-intensity exercise (MIE) at 60% ̇O2max and a sedentary control condition (CON). All exercise conditions were completed on a cycle ergometer and matched for time (30 min) and average intensity (60% ̇O2max). Brachial artery flow-mediated dilation (FMD) and CVR of the middle cerebral artery were measured before exercise, and 1- and 3-h after exercise. CVR was assessed using transcranial Doppler ultrasonography to both hypercapnia (6% carbon dioxide breathing) and hypocapnia (hyperventilation). FMD was significantly elevated above baseline 1 and 3 h following both HIIE conditions (P < 0.05), but FMD was unchanged following the MIE and CON trials (P > 0.33). CVR to both hypercapnia and hypocapnia, and when expressed across the end-tidal CO2 range, was unchanged in all conditions, at all time points (all P > 0.14). In conclusion, these novel findings show that the acute increases in peripheral vascular function following HIIE, compared with MIE, were not mirrored by changes in cerebrovascular reactivity, which was unaltered following all exercise conditions in healthy young adults. [ABSTRACT FROM AUTHOR]

The aim of this study was to compare the kinetic response of middle cerebral artery blood velocity (MCAv) to moderate- and heavy-intensity cycling in adults, and explore the relationship between maximal oxygen uptake (V_ O2max) and MCAv kinetics. Seventeen healthy adults (23.8 ± 2.4 yr, 9 females) completed a ramp incremental test to exhaustion on a cycle ergometer to determine V_ O2max and the gas exchange threshold (GET). Across six separate visits, participants completed three 6-min transitions at a moderate intensity (90% GET) and three at a heavy intensity (40% of the difference between GET and V_ O2max). Bilateral MCAv was measured using transcranial Doppler (TCD) ultrasonography and analyzed using a monoexponential model with a time delay. The time constant (s) of the MCAv response was not different between moderate- and heavy-intensity cycling (25 ± 10 vs. 26 ± 8 s, P = 0.82), as was the time delay (29 ± 11 vs. 29 ± 10 s, P = 0.95). The amplitude of the exponential increase in MCAv from baseline was greater during heavy-intensity cycling (23.9 ± 10.0 cm·s-1, 34.1 ± 14.4%) compared with moderate-intensity cycling (12.7 ± 4.4 cm·s-1, 18.7 ± 7.5%; P < 0.01). Following the exponential increase, a greater fall in MCAv was observed during heavy-intensity exercise compared with moderate-intensity exercise (9.5 ± 6.9 vs. 2.8 ± 3.8 cm·s-1, P < 0.01). MCAv after 6 min of exercise remained elevated during heavy-intensity exercise compared with moderate-intensity exercise (85.2 ± 9.6 vs. 79.3 ± 7.7 cm·s-1, P < 0.01). V_ O2max was not correlated with MCAv s or amplitude (r = 0.11–0.26, P > 0.05). These data suggest that the intensity of constant-work rate exercise influences the amplitude, but not time-based, response parameters of MCAv in healthy adults, and found no relationship between cardiorespiratory fitness and MCAv kinetics. [ABSTRACT FROM AUTHOR]

New Findings: What is the central question of the study?What is the reliability of middle cerebral artery velocity cerebrovascular reactivity (CVR) when using traditional and novel outcomes, as measured by transcranial Doppler?What is the main finding and its importance?Traditional CVR approaches presented acceptable reproducibility but should be expressed as an absolute CVR. Large within‐ and between‐individual differences in the middle cerebral artery velocity response profile support using a dynamic peak, rather than a set time point, for the most reliable interpretation. The study highlights the utility of novel kinetic CVR outcomes, but due to increased variability in time‐based metrics, this analysis requires larger sample sizes than traditional methods. Cerebrovascular reactivity (CVR) of middle cerebral artery velocity (MCAv) to CO2 is a common method to assess cerebrovascular function. Yet, the approaches used to calculate CVR outcomes vary. The aim of this study was to explore the within‐ and between‐day reliability of traditional CVR outcomes. The second aim was to explore the reliability of novel kinetic‐based analyses. Healthy adults (n = 10, 22.3 ± 3.4 years) completed assessments of CVR over 4 min using a fixed fraction of inspired CO2 (6%). This was repeated across four separate visits (between‐day), and on one visit measures were repeated 2.5 h later (within‐day). No mean biases were present between assessments for traditional CVR metrics, expressed as absolute (cm/s/mmHg) or relative (%/mmHg) outcomes (minute 3, minute 4, peak 1 s, peak 30 s) (between‐day: P > 0.14, ηp2 < 0.20; within‐day: P > 0.22, d > 0.27). Absolute, rather than relative, CVR yielded the most reproducible parameters (coefficient of variation: 8.1–13.2% vs. 14–83%, respectively). There were significant differences between CVR outcomes (P < 0.001, ηp2 > 0.89) dependent on the time point used to determine CVR, as a steady state MCAv response was rarely observed. Furthermore, the MCAv response was not reproducible within an individual (κ = 0.15, P = 0.09). No mean differences were present for novel kinetic outcomes (amplitude, time‐delay, time constant) (between‐day: P > 0.05, d < 0.33; within‐day: P > 0.38, d < 0.25). The results support the need for standardisation and indicate CVR should be defined as a dynamic peak, rather than a set time point for increased reliability. For novel kinetic outcomes variability was greater (CV: 8.7–120.9%) due to the nature of time‐based metrics. [ABSTRACT FROM AUTHOR]

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 (means ± SD age: 9.4 ± 0.9 yr), 14 adolescents (12.4 ± 0.4 yr), and 19 adults (23.4 ± 2.5 yr). Middle cerebral artery blood velocity (MCAv), partial pressure of end-tidal CO2 (PETCO2), and ventilatory parameters were analyzed 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 (V_E/VCO2 slope). Relative change from baseline (D%) in MCAv was lower in children, compared with 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). D%MCAv was similar in adults and adolescents at all intensities and similar in all groups at exhaustion. The magnitude of the VE/V CO2 slope was negatively associated with D%MCAv at GET and RCP across all participants (P ≤ 0.01, r = Δ0.37 to Δ0.48). D%PETCO2 was smaller in children and adolescents compared with adults at GET and RCP (P ≤ 0.05, d≥0.6). In children, D%PETCO2 and D%MCAv were not associated from baseline-GET (r = 0.14) and were moderately associated from RCP-exhaustion (r = 0.49). These relationships strengthened with increasing age and were stronger in adolescents (baseline-GET: r = 0.47, RCP-exhaustion: r = 0.62) and adults (baseline-GET: r = 0.66, RCP-exhaustion: r = 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. [ABSTRACT FROM AUTHOR]

The article discusses a study conducted to identify the acute macro-, micro- and cerebrovascular responses to glucose, fructose and sucrose consumption in ostensibly healthy adolescents. The study also analyzes whether sugar moiety influences the metabolic and vascular responses to a subsequent standardised meal challenge.

Purpose: Cerebrovascular reactivity (CVR) is impaired in adolescents with cardiovascular disease risk factors. A breath-hold test is a noninvasive method of assessing CVR, yet there are no reliability data of this outcome in youth. This study aimed to assess the reliability of a breath-hold protocol to measure CVR in adolescents.Methods: Twenty-one 13 to 15 year old adolescents visited the laboratory on two separate occasions, to assess the within-test, within-day and between-day reliability of a breath-hold protocol, consisting of three breath-hold attempts. CVR was defined as the relative increase from baseline in middle cerebral artery mean blood velocity following a maximal breath-hold of up to 30 seconds, quantified via transcranial Doppler ultrasonography.Results: Mean breath-hold duration and CVR were never significantly correlated (r < .31, P > .08). The within-test coefficient of variation for CVR was 15.2%, with no significant differences across breath-holds (P = .88), so the three breath-hold attempts were averaged for subsequent analyses. The within- and between-day coefficients of variation for CVR were 10.8% and 15.3%, respectively.Conclusions: CVR assessed via a three breath-hold protocol can be reliably measured in adolescents, yielding similar within- and between-day reliability. Analyses revealed that breath-hold length and CVR were unrelated, indicating the commonly reported normalization of CVR to breath-hold duration (breath-hold index) may be unnecessary in youth. [ABSTRACT FROM AUTHOR]

Endothelial dysfunction of the internal carotid artery (ICA) is a risk factor for cerebrovascular diseases (such as stroke, dementia and Alzheimer's disease), but whether brachial FMD is associated with cerebral endothelium-dependent vasodilation is unknown. These novel findings merit further discussion with respect to: (1) the lack of association between baseline cerebrovascular and peripheral artery shear-mediated function and (2) the lack of association between ICA endothelium-dependent function and traditional CVR outcomes. CVR tests are often considered to reflect cerebrovascular endothelial function, but these results indicate that "typical" CVR outcomes (ICA dilation, ICA-CVR and MCA-CVR expressed as %/mmHg) do not reflect shear-mediated ICA function. [Extracted from the article]