On the challenge of assessing dynamic cerebral autoregulation

Experimental Physiology, Journal Year: 2024, Volume and Issue: 109(7), P. 1020 - 1023

Published: May 7, 2024

Connections link a sequence of three related research papers. The central article which links the other two papers has been published in Experimental Physiology. In article, an author (or authors) outlines its principal novel findings, tracing how they were influenced by first and contributed to developments made third article. author(s) may also speculate on direction future field. articles aim set wide context. Dynamic cerebral autoregulation (dCA) represents ability cerebrovasculature respond transient changes arterial blood pressure (ABP). quantification dCA remains complex endeavour considering that gold-standard examine black-box nature this entity does not exist. Over years, investigators have applied numerous methods approaches used diverse metrics quantify based single change, or oscillations (spontaneous/forced), ABP (reviewed Brassard et al., 2023). Unfortunately, limited included multi-method strategies completed comparisons between analytical when assessing dCA. Distinctive stressors (e.g., spontaneous vs. forced oscillation; increase decrease ABP) can differently engage challenge regulatory mechanisms associated with dCA, thus providing different physiological information. As most appear unrelated each other, comparing findings across is challenging. To help illustrate interpreting using stresses methods, we will use results from reports focusing influence exercise training modalities (i.e., endurance resistance training) young healthy individuals. Endurance induce distinct adaptations, likely because haemodynamic responses induced these types. Generally, habitual leads beneficial cerebrovascular function such as resting perfusion carbon dioxide reactivity. However, existing evidence shows absence impact, even detrimental effects, some aspects function, These equivocal partly be consequence differences types participants. Despite modality-dependent responses, recent cross-sectional study suggest effect derived transfer analysis (TFA) velocity (CBv: surrogate flow) repeated squat–stands performed at 0.05 0.10 Hz (Perry 2019). objective TFA, popular method estimate variables reflecting dynamic behaviour supposing latter linear control system input (ABP) output (CBv). TFA are: coherence fraction linearly CBv), gain CBv amplitude change for given change), phase timing difference waveforms). Spontaneous rest) driven are utilized TFA. fluctuations attractive those who want populations whom it possible, safe, force larger (e.g. patients diseases). low signal-to-noise ratio) usually lead less reliable reproducible estimations Techniques, squat–stands, augment power enhance interpretability reproducibility metrics. shown vessels act high-pass filter, means slower than 0.20 dampened above pass through unimpeded. frequencies often literature forcing large (0.05 Hz) frequency bands where thought important pressure–flow dynamics (historically, being 0.02–0.07 very 0.07−0.20 frequency). Also, prevalent could reveal information about potential mechanisms. their study, Perry al. (2019) reported non-significant trend lowered resistance-trained individuals, compared endurance-trained sedentary suggesting no clear impact modality Do necessarily mean cannot dCA? One must consider assumes symmetric, case. For instance, accumulating clearly suggests react increases, comparison decreases, ABP. Specifically, elevations attenuated increases. This phenomenon steady-state changes, well oscillations. all take into consideration (TFA example). Our group recently suggested utilization directional sensitivity metric non-pharmacological approach relationship increases decreases. series studies (detailed below), middle artery (MCAv) (MAP) higher Hz: indicative sympathetic tone Mayer waves) only. same cohort endurance- individuals (2019), subsequently quantified our proposed (Roy 2022). calculated absolute (ΔMCAvT/ΔMAPT) relative (%MCAvT/%MAPT) respect transition time intervals both calculate time-adjusted ratio MAP direction, averaged over 5-min squat–stands. Using analysis, ΔMCAvT/ΔMAPT %MCAvT/%MAPT lower during decreases but participants ratios sedentary, Hz, previously influences directionality specifically participants, presence selectively defends microcirculation overperfusion surges. hysteresis-like pattern interpreted alternatively, improved Considering did provide groups 2019), represent more sensitive detect changes. sharp contrast longitudinal examined (Thomas 2021). cross-over design 68 young, randomized complete 3 months modality, following comparable mentioned, offer greater coherence, addition Accordingly, robust stressor quantifying aspect via Although seems promising relationship, further warranted experimental conditions clinical/pathological flesh out key logistical aspects. double-ratio calculation validated truly reflect flow regulation, additional work necessary whether, hypercapnia, hypoxia hyperthermia, conditions, ageing, cardiovascular diseases. Interestingly, exist characterize relationship. example, previous work, squat–stand model only described better response autoregulatory index. Panerai (2023) new autoregressive-moving average models dividing signal components—first including beat-to-beat positive derivative information, then corresponding negative time-series. contrary advantage method, relatively small (Panerai Discrepancies 2022) methodological drive depth squat was (participants went 45-degree knee flexion angle) al.'s squatted down felt able) Alternatively, pointed (which tends oscillations) They argue sample size (n = 12/group) too low, bootstrap procedure evaluate number needed identify significant (critical number: n 24 squat–stands) Both reasons why detected Hz. A next logical step would compare analyses within performing one appreciate, population (in case, endurance-trained, individuals) (spontaneous analysis) interpretations. while Thomas (2021) do optimal strategy knowing high variability poor Finally, although improves searching alternatives crucial consideration, exists support sensitivity. We still early stages assessment, here again, squat–stands). Continued efforts find best metric, collection several stresses, adequately assess improve interpretation All authors read approved final version manuscript agree accountable ensuring questions accuracy integrity any part appropriately investigated resolved. persons designated qualify authorship, authorship listed. declare conflicts interest. No funding received work.

Language: Английский

Larger reductions in blood pressure during post‐exercise standing, but not middle cerebral artery blood velocity, in resistance‐trained versus untrained individuals

Experimental Physiology, Journal Year: 2024, Volume and Issue: unknown

Published: Dec. 25, 2024

Abstract Dynamic resistance exercise (RE) produces sinusoidal fluctuations in blood pressure, with hypotension and cerebral hypoperfusion commonly observed immediately following RE. Whether the vasculature adapts to these regular pressure challenges is unclear. This study examined cerebrovascular response post‐dynamic RE orthostasis. RE‐trained ( n = 15, female 4) healthy untrained individuals 12) completed five stands: one after seated rest, each of subsequent four stands occurring a set 10 repetitions unilateral leg extension at 60% their repetition maximum. Beat‐to‐beat mean middle artery velocity (MCAv ) end‐tidal carbon dioxide were measured throughout. During standing arterial (MAP) MCAv nadirs identified. There was no difference between groups for age (mean ± SD, 26 7 vs. 25 6 years untrained, P 0.683) or weight (78 15 71 kg, 0.683). At MAP nadir during post‐exercise stand, greater reduction group (e.g., 4, −45 11 −36 mmHg, training effect 0.026). However, stand not different −20 −17 cm/s, interaction 0.478). Rate regulation higher (set 1, 0.301 0.170 0.167 0.009, 0.023). Despite demonstrating absolute reductions orthostasis RE, there differences , suggesting that habitual may mitigate hypoperfusion.

Language: Английский