Greater increase in internal carotid artery shear rate during aerobic interval compared to continuous exercise in healthy adult men

Acute aerobic exercise enhances cerebrovascular shear-mediated dilation in young adults: the role of cerebral shear

Exercise-induced increases in shear rate (SR) acutely improve peripheral endothelial function, but the presence of this mechanism in cerebral arteries remains unclear. Thus, we evaluated shear-mediated dilation of the internal carotid artery (ICA), which is an index of cerebrovascular endothelial function, before and after exercise. Shear-mediated dilation was measured with 30 s of hypercapnia in 16 young adults before and 10 min after 30 min of sitting rest (CON) or three cycling exercises on four separate days. The target exercise intensity was 80% of oxygen uptake at the ventilatory threshold. To manipulate the ICA SR during exercise, participants breathed spontaneously (ExSB, SR increase) or hyperventilated without (ExHV, no increase in SR) or with ([Formula: see text], restoration of SR increase) addition of CO2 to inspiratory air. Shear-mediated dilation was calculated as a percent increase in diameter from baseline. Doppler ultrasound measures ICA velocity and diameter. The CON trial revealed that 30 min of sitting did not alter shear-mediated dilation (4.34 ± 1.37% to 3.44 ± 1.23%, P = 0.052). ICA dilation after exercise compared with preexercise levels increased in the ExSB trial (3.32 ± 1.37% to 4.74 ± 1.84%, P < 0.01), remained unchanged in the ExHV trial (4.07 ± 1.55% to 3.21 ± 1.48%, P = 0.07), but was elevated in the [Formula: see text] trial (3.35 ± 1.15% to 4.33 ± 2.12%, P = 0.04). Our results indicate that exercise-induced increases in cerebral shear may play a crucial role in improving cerebrovascular endothelial function after acute exercise in young adults.NEW & NOTEWORTHY We found that 30-min cycling (target intensity was 80% of the ventilatory threshold) with increasing shear of the internal carotid artery (ICA) enhanced transient hypercapnia-induced shear-mediated dilation of the ICA, reflecting improved cerebrovascular endothelial function. This enhancement of ICA dilation was diminished by suppressing the exercise-induced increase in ICA shear via hyperventilation. Our results indicate that increases in cerebral shear may be a key stimulus for improving cerebrovascular endothelial function after exercise in young adults.

Effects of high-intensity intermittent exercise versus moderate-intensity continuous exercise on renal hemodynamics assessed by ultrasound echo

High-intensity intermittent exercise (HIIE) has become attractive for presenting a variety of exercise conditions. However, the effects of HIIE on renal function and hemodynamics remain unclear. This study aimed to compare the effects of HIIE and moderate-intensity continuous exercise (MICE) on renal hemodynamics, renal function, and kidney injury biomarkers. Ten adult males participated in this study. We allowed the participants to perform HIIE or MICE to consider the impact of exercise on renal hemodynamics under both conditions. Renal hemodynamic assessment and blood sampling were conducted before the exercise (pre) and immediately (post 0), 30 min (post 30), and 60 min (post 60) after the exercise. Urine sampling was conducted in the pre, post 0, and post 60 phases. There was no condition-by-time interaction (p = 0.614), condition (p = 0.422), or time effect (p = 0.114) regarding renal blood flow. Creatinine-corrected urinary neutrophil gelatinase-associated lipocalin concentrations increased at post 60 (p = 0.017), but none exceeded the cut-off values for defining kidney injury. Moreover, there were no significant changes in other kidney injury biomarkers at any point. These findings suggest that high-intensity exercise can be performed without decreased RBF or increased kidney injury risk when conducted intermittently for short periods.

Handgrip exercise does not alter CO2 -mediated cerebrovascular flow-mediated dilation

Handgrip exercise (HG), a small muscle exercise, improves cognitive function and is expected to provide a useful exercise mode to maintain cerebral health. However, the effect of HG on cerebral blood flow regulation is not fully understood. The present study aimed to examine the effect of acute HG on cerebral endothelial function as one of the essential cerebral blood flow regulatory functions. Thirteen healthy young participants performed interval HG, consisting of 4 sets of 2 min HG at 25% of maximum voluntary contraction with 3 min recovery between each set. Cognitive performance was evaluated before and at 5 and 60 min after interval HG using the Go/No-Go task (reaction time and accuracy). The diameter and blood velocity of the internal carotid artery (ICA) were measured using a duplex Doppler ultrasound system. To assess cerebral endothelial function, hypercapnia (30 s of hypercapnia stimulation, end-tidal partial pressure of CO2 : +9 mmHg)-induced cerebrovascular flow-mediated dilatation (cFMD) was induced, calculated as relative peak dilatation from baseline diameter. The shear rate (SR) was calculated using the diameter and blood velocity of the ICA. As a result, cognitive performance improved only at 5 min after interval HG (reaction time, P = 0.008; accuracy, P = 0.186), whereas ICA SR during interval HG and cFMD after interval HG were unchanged (P = 0.313 and P = 0.440, respectively). These results suggest that enhancement in cerebral endothelial function is not an essential mechanism responsible for acute HG-induced cognitive improvement. NEW FINDINGS: What is the central question of this study? Does handgrip exercise, a small muscle exercise, improve cerebral endothelial function? What is the main finding and its importance? Acute interval isometric handgrip exercise (2 min of exercise at 25% maximum voluntary contraction, followed by 3 min of recovery, repeated for a total of 4 sets) did not improve cerebral endothelial function. Since the cerebrovascular shear rate did not change during exercise, it is possible that acute handgrip exercise is not sufficient stimulation to improve cerebral endothelial function.

Attenuated pulsatile transition to the cerebral vasculature during high-intensity interval exercise in young healthy men

NEW FINDINGS

What is the central question of this study? High-intensity interval exercise (HIIE) is recommended for its favourable haemodynamic stimulation, but excessive haemodynamic fluctuations may stress the brain: is the cerebral vasculature protected against exaggerated systemic blood flow fluctuation during HIIE? What is the main finding and its importance? Time- and frequency-domain indices of aortic-cerebral pulsatile transition were lowered during HIIE. The findings suggest that the arterial system to the cerebral vasculature may attenuate pulsatile transition during HIIE as a defence mechanism against pulsatile fluctuation for the cerebral vasculature.

ABSTRACT

High-intensity interval exercise (HIIE) is recommended because it provides favourable haemodynamic stimulation, but excessive haemodynamic fluctuations may be an adverse impact on the brain. We tested whether the cerebral vasculature is protected against systemic blood flow fluctuation during HIIE. Fourteen healthy men (age 24 ± 2 years) underwent four 4-min exercises at 80-90% of maximal workload (Wmax ) interspaced by 3-min active rest at 50-60% Wmax . Transcranial Doppler measured middle cerebral artery blood velocity (CBV). Systemic haemodynamics (Modelflow) and aortic pressure (AoP, general transfer function) were estimated from an invasively recorded brachial arterial pressure waveform. Using transfer function analysis, gain and phase between AoP and CBV (0.39-10.0 Hz) were calculated. Stroke volume, aortic pulse pressure and pulsatile CBV increased during exercise (time effect: P < 0.0001 for all), but a time-domain index of aortic-cerebral pulsatile transition (pulsatile CBV/pulsatile AoP) decreased throughout the exercise bouts (time effect: P < 0.0001). Furthermore, transfer function gain reduced, and phase increased throughout the exercise bouts (time effect: P < 0.0001 for both), suggesting the attenuation and delay of pulsatile transition. The cerebral vascular conductance index (mean CBV/mean arterial pressure; time effect: P = 0.296), an inverse index of cerebral vascular tone, did not change even though systemic vascular conductance increased during exercise (time effect: P < 0.0001). The arterial system to the cerebral vasculature may attenuate pulsatile transition during HIIE as a defence mechanism against pulsatile fluctuation for the cerebral vasculature.

Dynamic resistance exercise-induced pressor response does not alter hypercapnia-induced cerebral vasodilation in young adults

Excessive arterial pressure elevation induced by resistance exercise (RE) attenuates peripheral vasodilatory function, but its effect on cerebrovascular function is unknown. We aimed to evaluate the effect of different pressor responses to RE on hypercapnia-induced vasodilation of the internal carotid artery (ICA), an index of cerebrovascular function. To manipulate pressor responses to RE, 15 healthy young adults (11M/4F) performed two RE: high intensity with low repetitions (HL) and low intensity with high repetitions (LH) dynamic knee extension. ICA dilation, induced by 3 min of hypercapnia, was measured before and 10 min after RE using Doppler ultrasound. HL exercise elicited a greater pressor response than LH exercise. In relaxation phases of RE, ICA blood velocity increased in both HL and LH trials. However, ICA shear rate did not significantly increase in either trial (P = 0.06). Consequently, neither exercise altered post-exercise hypercapnia-induced ICA dilation (HL, 3.9 ± 1.9% to 5.1 ± 1.7%; LH, 4.6 ± 1.4% to 4.8 ± 1.8%; P > 0.05 for all). When viewed individually, the changes in ICA shear rate were positively correlated with changes in end-tidal partial pressure of carbon dioxide (P_ETCO₂) (r = 0.46, P < 0.01) than with mean arterial pressure (r = 0.32, P = 0.02). These findings suggest that the effects of RE-induced pressor response on cerebrovascular function may be different from peripheral arteries. An increase in P_ETCO₂ during the relaxation phase may play a more crucial role than elevated pressure in increasing cerebral shear during dynamic RE.

The Utility of High Intensity Interval Training to Improve Cognitive Aging in Heart Disease Patients

Adults with cardiovascular disease and heart failure are at higher risk of cognitive decline. Cerebral hypoperfusion appears to be a significant contributor, which can result from vascular dysfunction and impairment of cerebral blood flow regulation. In contrast, higher cardiorespiratory fitness shows protection against brain atrophy, reductions in cerebral blood flow, and cognitive decline. Given that high intensity interval training (HIIT) has been shown to be a potent stimulus for improving cardiorespiratory fitness and peripheral vascular function, its utility for improving cognitive aging is an important area of research. This article will review the physiology related to cerebral blood flow regulation and cognitive decline in adults with cardiovascular disease and heart failure, and how HIIT may provide a more optimal stimulus for improving cognitive aging in this population.

Effects of continuous hypoxia on flow-mediated dilation in the cerebral and systemic circulation: on the regulatory significance of shear rate phenotype

Emergent evidence suggests that cyclic intermittent hypoxia increases cerebral arterial shear rate and endothelial function, whereas continuous exposure decreases anterior cerebral oxygen (O₂) delivery. To examine to what extent continuous hypoxia impacts cerebral shear rate, cerebral endothelial function, and consequent cerebral O₂ delivery (CDO₂), eight healthy males were randomly assigned single-blind to 7 h passive exposure to both normoxia (21% O₂) and hypoxia (12% O₂). Blood flow in the brachial and internal carotid arteries were determined using Duplex ultrasound and included the combined assessment of systemic and cerebral endothelium-dependent flow-mediated dilatation. Systemic (brachial artery) flow-mediated dilatation was consistently lower during hypoxia (P = 0.013 vs. normoxia), whereas cerebral flow-mediated dilation remained preserved (P = 0.927 vs. normoxia) despite a reduction in internal carotid artery antegrade shear rate (P = 0.002 vs. normoxia) and CDO₂ (P < 0.001 vs. normoxia). Collectively, these findings indicate that the reduction in CDO₂ appears to be independent of cerebral endothelial function and contrasts with that observed during cyclic intermittent hypoxia, highlighting the regulatory importance of (hypoxia) dose duration and flow/shear rate phenotype.