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Individuals who experience prolonged sitting daily are reported to be at risk of developing cerebrovascular disease, which is associated, in part, with attenuation in cerebral blood flow regulation. However, the effect of prolonged sitting on dynamic cerebral autoregulation (dCA), a crucial mechanism of cerebral blood flow regulation, remains unclear. Additionally, cerebrovascular disease occurs heterogeneously within cerebral arteries. The purpose of the present study was to examine the hypothesis that prolonged sitting attenuates dCA in the cerebral circulation heterogeneously. Twelve young, healthy participants were instructed to maintain a seated position for 4 h without moving their lower limbs. Mean arterial pressure and mean blood velocities of the middle cerebral artery (MCA Vm) and the posterior cerebral artery (PCA Vm) were measured continuously throughout the experiment. The dCA was assessed using transfer function analysis (TFA) with mean arterial pressure and either MCA Vm or PCA Vm. In the MCA, very low‐frequency TFA‐normalized gain decreased significantly during 4 h of prolonged sitting (P = 0.029), indicating an improvement rather than attenuation in dCA, despite a significant reduction in MCA Vm after 4 h of continuous sitting (P = 0.039). In the PCA, PCA Vm remained stable throughout the 4 h sitting period (P = 0.923), and all TFA parameters remained unchanged throughout the 4 h of sitting. Contrary to our hypothesis, these results suggest that the dCA in both the MCA and the PCA was well stabilized in healthy young individuals during acute prolonged sitting. [ABSTRACT FROM AUTHOR]

There are differences within the literature regarding the upper frequency cut‐off point of the dynamic cerebral autoregulation (CA) high‐pass filter. The projection pursuit regression approach has demonstrated that the upper frequency limit is ∼0.07 Hz, whereas another approach [transfer function analysis (TFA) phase approaching zero] indicated a theoretical upper frequency limit for the high‐pass filter of 0.24 Hz. We investigated how these limits accurately represent the CA upper frequency limit, in addition to extending earlier findings with respect to biological sexes and across the cardiac cycle. Sixteen participants (nine females and seven males) performed repeated squat–stand manoeuvres at frequencies of 0.05, 0.10, 0.15, 0.20 and 0.25 Hz, with insonation of the middle and posterior cerebral arteries. Linear regression modelling with adjustment for sex and order of squat completion was used to compared TFA gain and phase with 0.25 Hz (above the theoretical limit of CA). The upper frequency limit of CA with TFA gain was within the range of 0.05–0.10 Hz, whereas TFA phase was within the range of 0.20–0.25 Hz, and consistent between vessels, between sexes and across the cardiac cycle. Females displayed greater middle cerebral artery gain compared with males (all P < 0.047), and no phase differences were present (all P > 0.072). Although sex‐specific differences were present for specific TFA metrics at a given frequency, the upper frequency limit of autoregulation was similar between cerebral conduit vessels, cardiac cycle phase and biological sex. Future work is warranted to determine whether an upper frequency limit exists with respect to hysteresis analyses. [ABSTRACT FROM AUTHOR]

This article discusses the challenge of assessing dynamic cerebral autoregulation (dCA), which refers to the ability of the cerebrovasculature to respond to changes in arterial blood pressure. The quantification of dCA is complex and lacks a gold-standard method. The article highlights the need for multi-method strategies and comparisons between analytical approaches when assessing dCA. It also explores the influence of different exercise training modalities on dCA and discusses the limitations of current analytical methods, such as transfer function analysis (TFA). The authors propose a directional sensitivity metric as a potentially more sensitive method to detect cerebral haemodynamic changes. However, further research is needed to validate this metric and explore its applicability in different conditions and populations. The article emphasizes the importance of finding the best metric or collection of metrics to accurately assess dCA and improve the understanding of the cerebral pressure-flow relationship. [Extracted from the article]

Transfer function analysis (TFA) is a commonly used method to measure dynamic cerebral autoregulation (dCA), which assesses the ability of the brain's blood vessels to regulate changes in arterial blood pressure (ABP). However, the reliability of TFA metrics calculated from spontaneous ABP oscillations is limited compared to forced oscillations. A study in Experimental Physiology found that a 5-minute recording of spontaneous ABP and cerebral blood velocity (CBv) oscillations is insufficient for stable and reliable TFA metrics, particularly in patients with subarachnoid hemorrhage and sepsis. The authors suggest using methods to induce ABP fluctuations, such as repeated squat-stands, to improve TFA interpretability. However, the study has limitations, such as the lack of continuous measurement of carbon dioxide levels and potential medication effects. Overall, researchers and clinicians may need to explore alternative analytical strategies, such as wavelet synchronization, for quantifying dCA using spontaneous ABP and CBv. [Extracted from the article]

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. 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. [ABSTRACT FROM AUTHOR]

Chronic Kidney Disease (CKD) patients experience an elevated risk for cerebrovascular disease. One factor that may contribute to this heightened risk is an impairment in dynamic cerebral autoregulation, the mechanism by which cerebral vessels modulate cerebral blood flow during fluctuations in arterial pressure. We hypothesized that dynamic cerebral autoregulation would be impaired in CKD. To test this hypothesis, we compared dynamic cerebral autoregulation between CKD patients stages III‐IV and matched controls (CON) without CKD. Fifteen patients with CKD and 20 CON participants performed 2, 5‐minute bouts of repeated sit‐to‐stand maneuvers at 0.05 Hz and 0.10 Hz while mean arterial pressure (MAP, via finger photoplethysmography) and middle cerebral artery blood velocity (MCAv, via transcranial Doppler ultrasound) were measured continuously. Cerebral autoregulation was characterized by performing a transfer function analysis (TFA) on the MAP‐MCAv relationship to derive coherence, phase, gain, and normalized gain (nGain). We observed no group differences in any of the TFA metrics during the repeated sit‐to‐stand maneuvers. During the 0.05 Hz maneuver, Coherence: CKD = 0.83 ± 0.13, CON = 0.85 ± 0.12, Phase (radians): CKD = 1.39 ± 0.41, CON = 1.25 ± 0.30, Gain (cm/s/mmHg): CKD = 0.69 ± 0.20, CON = 0.71 ± 0.22, nGain (%/mmHg): CKD = 1.26 ± 0.35, CON = 1.20 ± 0.28, p ≥ 0.24. During the 0.10 Hz maneuver (N = 6 CKD and N = 12 CON), Coherence: CKD = 0.61 ± 0.10, CON = 0.67 ± 0.11, Phase (radians): CKD = 1.43 ± 0.26, CON = 1.30 ± 0.23, Gain (cm/s/mmHg): CKD = 0.75 ± 0.15, CON = 0.84 ± 0.26, nGain (%/mmHg): CKD = 1.50 ± 0.28, CON = 1.29 ± 0.24, p ≥ 0.12. Contrary to our hypothesis, dynamic cerebral autoregulation remains intact in CKD stages III‐IV. These findings suggest that other mechanisms likely contribute to the increased cerebrovascular disease burden experienced by this population. Future work should determine if other cerebrovascular regulatory mechanisms are impaired and related to cerebrovascular disease risk in CKD. [ABSTRACT FROM AUTHOR]

In patients with sickle cell disease (SCD), the delivery of oxygen to the brain is compromised by anemia, abnormal rheology, and steno‐occlusive vascular disease. Successful compensation depends on an increase in oxygen supply such as that provided by an increase in cerebral blood flow (CBF). We used magnetic resonance imaging to provide a high‐resolution assessment of the ability of SCD patients to respond to a vasoactive stimulus in middle, anterior, and posterior cerebral artery territories for both white and gray matter. Cerebrovascular reactivity (CVR) was measured as the blood oxygen level dependent signal (a surrogate for CBF) response to an increase in the end tidal partial pressure of CO2 (PETCO2). The dynamic aspect of the response was measured as the time constant of the first order response kinetics (tau). To confirm and support these findings we used an alternative examination of the response, transfer function analysis (TFA), to measure the responsiveness (gain), the speed of response (phase), and the consistency of the response over time (coherence). We tested 34 patients with SCD and compared the results to those of 24 healthy controls participants. The results from a three‐way ANOVA showed that patients with SCD have reduced CVR (p < 0.001) and lower coherence (p < 0.001) in gray matter and white matter and reduced gain in gray matter only (p < 0.001). In terms of the speed of the response to CO2, tau (p < 0.001) and TFA phase (p < 0.001) were increased in SCD patients compared to healthy control subjects. These findings show that the cerebrovascular responsiveness to CO2 in patients with SCD is both decreased and slowed compared to healthy controls. [ABSTRACT FROM AUTHOR]

Dynamic cerebral autoregulation to spontaneous fluctuations in cerebral perfusion pressure (CPP) is often assessed by transcranial Doppler (TCD) in the time domain, yielding primarily the mean flow index (Mx), or in the frequency domain using transfer function analysis (TFA), yielding gain and phase. For both domains, the measurement of blood pressure is critical. This study assessed the inter‐method reliability of dynamic cerebral autoregulation using three different methods of pressure measurement. In 39 patients with aneurysmal subarachnoid hemorrhage, non‐invasive arterial blood pressure (ABP), invasive ABP (measured in the radial artery) and CPP were recorded simultaneously with TCD. Intraclass correlation coefficient (ICC) was used to quantify reliability. Mx was higher when calculated using invasive ABP (0.39; 95% confidence interval [95% CI]: 0.33; 0.44) compared to non‐invasive ABP, and CPP. The overall ICC showed poor to good reliability (0.65; 95% CI: 0.11; 0.84; n = 69). In the low frequency domain, the comparison between invasively measured ABP and CPP showed good to excellent (normalized gain, ICC: 0.87, 95CI: 0.81; 0.91; n = 96; non‐normalized gain: 0.89, 95% CI: 0.84; 0.92; n = 96) and moderate to good reliability (phase, ICC: 0.69, 95% CI: 0.55; 0.79; n = 96), respectively. Different methods for pressure measurement in the assessment of dynamic cerebral autoregulation yield different results and cannot be used interchangeably. [ABSTRACT FROM AUTHOR]

Aims: Cerebral small vessel disease (CSVD) is characterized by functional and structural changes in small vessels. We aimed to elucidate the relationship between dynamic cerebral autoregulation (dCA) and neuroimaging characteristics of CSVD. Methods: A case‐control study was performed. Cerebral blood flow velocity (CBFV) of bilateral middle cerebral arteries and spontaneous arterial blood pressure were simultaneously recorded. Transfer function analysis was used to calculate dCA parameters (phase, gain, and the rate of recovery of CBFV [RoRc]). Neuroimaging characteristics of CSVD patients were evaluated, including lacunes, white matter hyperintensities (WMH), cerebral microbleeds (CMBs), perivascular spaces (PVS), and the total CSVD burden. Results: Overall, 113 patients and 83 controls were enrolled. Compared with the control group, the phase at low frequency and the RoRc in CSVD patients were lower, and the gain at very low and low frequencies were higher, indicating bilaterally impaired dCA. Total CSVD burden, WMH (total, periventricular and deep), severe PVS, and lobar CMBs were independently correlated with the phase at low frequency. Conclusions: Our findings suggested that dCA was compromised in CSVD patients, and some specific neuroimaging characteristics (the total CSVD burden, WMH, severe PVS and lobar CMBs) might indicate more severe dCA impairment in CSVD patients. [ABSTRACT FROM AUTHOR]

The incidence of depression is increasing, especially in the young adult population. Impaired cognitive function is one of the characteristics of depression, which may be related to impaired cerebral autoregulation (CA). We investigated the characteristics of CA in young adults with mild depression, as well as its validity for identifying patients with depression. Patients (aged 18–35 years) with Hamilton Depression Rating Scale (HAMD) scores ranging from 8 to 17 and a first episode of mild depression were enrolled in this study. Healthy volunteers were recruited as controls. Noninvasive continuous arterial blood pressure and bilateral middle cerebral artery blood flow velocity were simultaneously recorded from each subject. Transfer function analysis was applied to derive phase difference, gain, coherence and rate of recovery for the assessment of CA. Forty‐three patients and 43 healthy controls were enrolled. Phase difference values were significantly compromised in young adults with mild depression and were negatively correlated with HAMD scores. Rate of recovery values estimated from depressed patients was significantly lower. The validity in identifying patients with depression was favorable for the phase difference. The cutoff phase difference value was 29.66. Our findings suggest that dynamic CA was impaired in young patients with mild depression and negatively correlated with HAMD scores. CA represented by phase difference can be used as an objective auxiliary examination of depression, and has clinical diagnostic value for the early identification of patients with depression. Cognitive impairment is one of the most common features of depression, which may be related to impaired cerebral autoregulation (CA). The current study, for the first time, investigated the characteristics of CA in young adults with mild depression. The findings suggested that dynamic CA was compromised in young patients with mild depression. CA represented by phase difference has clinical diagnostic value for the early identification of patients with depression. [ABSTRACT FROM AUTHOR]

New Findings: What is the central question of this study?What are the dynamic characteristics of cerebrovascular carbon dioxide reactivity and the central respiratory chemoreflex?What is the main finding and its importance?The transfer function gain from the end‐tidal partial pressure of carbon dioxide to cerebral blood flow or ventilation decreased in the high frequency range at rest and during exercise. These findings indicate that the dynamic characteristics of both systems were not constant in all frequency ranges, and this trend was not modified by exercise. The purpose of this study was to examine the dynamic characteristics of cerebrovascular reactivity and ventilatory response to change in arterial CO2 in all frequency ranges at rest using frequency domain analysis, and also to examine whether this is modified by dynamic exercise as with the traditionally determined cerebrovascular CO2 reactivity. In nine healthy young subjects, at rest and during exercise (cycling exercise at constant predetermined work rate corresponding to a V̇O2 level of 0.90 l min−1), the dynamic characteristics of cerebrovascular CO2 reactivity and the central respiratory chemoreflex were assessed by transfer function analysis using a binary white‐noise sequence (0–7% inspired CO2 fraction) from the end‐tidal partial pressure of CO2 (PETCO2) to the mean middle cerebral artery mean blood velocity (MCA Vm) or minute ventilation (V̇E), respectively. In the high frequency range, both transfer function gains decreased but, interestingly, the cut‐off frequency in the transfer function gain from PETCO2 to MCA Vm response was higher than that from PETCO2 to V̇E response at rest (0.024 vs. 0.015 Hz) and during exercise (0.030 vs. 0.011 Hz), indicating that cerebrovascular CO2 reactivity or central respiratory chemoreflex was not constant in all frequency ranges, and this trend was not modified by exercise. These findings suggest that dynamic characteristics of the cerebrovascular CO2 reactivity or central chemoreflex need to be assessed to identify the whole system because the traditional method cannot identify the property of time response of these systems. [ABSTRACT FROM AUTHOR]

Repeated squat‐stand maneuvers (SSM) are an effective way of measuring dynamic cerebral autoregulation (dCA), but the depth of SSM required to improve dCA estimations has never been studied. We compared beat‐to‐beat cerebral hemodynamic parameters between maximal depth SSM (SSMD) and a shallower alternative (SSMS) in two age groups (younger [20–34 years] vs. older [50–71 years]) at a frequency of 0.05 Hz. Cerebral blood flow velocity, continuous blood pressure (BP) and end‐tidal CO2 (EtCO2) were measured using transcranial Doppler ultrasound, the Finometer device, and capnography, respectively. Coherence (at 0.05 Hz) was significantly higher in both SSM recordings compared to spontaneous BP oscillations at baseline standing (BS). Median (IQR) autoregulation index (ARI) was reduced during SSMD (4.46 [4.03–5.22], p <.01) compared to SSMS (5.96 [5.40–6.69]) and BS (6.03 [5.20–6.49], p <.01) with similar relative differences also observed for phase (at 0.05 Hz). End‐tidal CO2 was increased in SSMD (38.3 ± 3.7 mmHg, p <.01) compared to both SSMS (36.6 ± 3.6 mmHg) and BS (35.5 ± 3.2 mmHg). The older group demonstrated significantly lower ARI and phase estimates during SSM and found SSMS more effortful than SSMD. In conclusion, both SSMD and SSMS are effective at estimating dCA, and dCA appears to be less efficient during maximal depth SSM compared to baseline rest or a shallower alternative. [ABSTRACT FROM AUTHOR]

New Findings: What is the central question of this study?Does habitual resistance and endurance exercise modify dynamic cerebral autoregulation?What is the main finding and its importance?To the authors' knowledge, this is the first study to directly assess dynamic cerebral autoregulation in resistance‐trained individuals, and potential differences between exercise training modalities. Forced oscillations in blood pressure were induced by repeated squat–stands, from which dynamic cerebral autoregulation was assessed using transfer function analysis. These data indicate that dynamic cerebral autoregulatory function is largely unaffected by habitual exercise type, and further document the systemic circulatory effects of regular exercise. Regular endurance and resistance exercise produce differential but desirable physiological adaptations in both healthy and clinical populations. The chronic effect of these different exercise modalities on cerebral vessels' ability to respond to rapid changes in blood pressure (BP) had not been examined. We examined dynamic cerebral autoregulation (dCA) in 12 resistance‐trained (mean ± SD, 25 ± 6 years), 12 endurance‐trained (28 ± 9 years) and 12 sedentary (26 ± 6 years) volunteers. The dCA was assessed using transfer function analysis of forced oscillations in BP vs. middle cerebral artery blood velocity (MCAv), induced via repeated squat–stands at 0.05 and 0.10 Hz. Resting BP and MCAv were similar between groups (interaction: both P ≥ 0.544). The partial pressure of end‐tidal carbon dioxide (P ETC O2) was unchanged (P = 0.561) across squat–stand manoeuvres (grouped mean for absolute change +0.6 ± 2.3 mmHg). Gain and normalized gain were similar between groups across all frequencies (both P ≥ 0.261). Phase showed a frequency‐specific effect between groups (P = 0.043), tending to be lower in resistance‐trained (0.63 ± 0.21 radians) than in endurance‐trained (0.90 ± 0.41, P = 0.052) and ‐untrained (0.85 ± 0.38, P = 0.081) groups at slower frequency (0.05 Hz) oscillations. Squat–stands induced mean arterial pressure perturbations differed between groups (interaction: P = 0.031), with greater changes in the resistance (P < 0.001) and endurance (P = 0.001) groups compared with the sedentary group at 0.05 Hz (56 ± 13 and 49 ± 11 vs. 35 ± 11 mmHg, respectively). The differences persisted at 0.1 Hz between resistance and sedentary groups (49 ± 12 vs. 33 ± 7 mmHg, P < 0.001). These results indicate that dCA remains largely unaltered by habitual endurance and resistance exercise with a trend for phase to be lower in the resistance exercise group at lower fequencies. [ABSTRACT FROM AUTHOR]

A novel microstrip lowpass filter with outstanding features is designed, simulated, fabricated and analysed. The proposed structure has the capability to improve frequency response in transition band and remove the 13th unwanted harmonics in the stopband. The proposed design comprises many resonators and cell attenuators. It features an UW stopband, high suppression factor and high sharp roll‐off. To adjust the cut‐off frequency, the transfer function and LC equivalent circuit of the main resonator are calculated. Results show that cut‐off frequency and relative bandwidth of stopband of the filter are 2 GHz and 171%, respectively. Also, insertion loss <0.11 dB and return loss more than 18 dB have obtained for filter form DC to 2 GHz. The fabricated filter reaches a high figure of merit of 72,093. [ABSTRACT FROM AUTHOR]

1. Perturbation analyses of population projection matrices predict the response of a population’s growth rate to changes in lifestage-specific vital rates. Such predictions have been widely used in population management but their reliability remains hotly debated. 2. We grew replicate populations of the water flea Daphnia magna in controlled, density-independent conditions and subjected treatment populations to harvesting of the largest lifestage. We predicted the growth rate of treatment populations using sensitivity analysis (a linear approximation), and transfer function analysis (TFA; which captures nonlinear responses) applied to projection matrix models parameterized from the control populations. 3. When perturbation analyses considered only the direct effect of harvesting on adult survival, the growth rate of harvested populations (averaging 0·051) was significantly overestimated (average of 0·112) by TFA and non-significantly underestimated (average of 0·012) by sensitivity. 4. When the indirect effects of harvesting on other vital rates were accounted for in a structured perturbation, TFA gave accurate predictions (average growth rate of 0·068), while sensitivity gave significant underestimates (average of −0·043). 5. Our results demonstrate two crucial sources of error that may influence predictions of the impacts of demographic perturbations on population dynamics. First, impacts of stage-specific harvesting are inherently nonlinear, hence predictions based on sensitivity must be treated with caution. Second, stage-specific perturbations can change non-target demographic rates, even in the absence of adaptation. 6. Population managers should consider both nonlinear and indirect effects of perturbations when designing management interventions. We encourage the development of methods to assess the robustness of predictions to unforeseen perturbation structures and indirect harvesting impacts. [ABSTRACT FROM AUTHOR]

Eclampsia is frequently associated with brain edema, cerebral infarction or hemorrhage. Its underlying cerebrovascular pathophysiology is still poorly understood. We examined cerebral autoregulation by a non-invasive multimodal assessment in a 28-year-old primaparous woman with postpartal eclampsia. Transcranial Doppler sonography showed considerably increased cerebral blood flow velocity (CBFV) of all basal cerebral vessels. Magnetic resonance imaging demonstrated multifocal vasogenic brain edema. Using transfer function analysis, a severely decreased phase shift between respiratory-induced 0.1-Hz oscillations of arterial blood pressure and CBFV was observed, indicating substantial disturbance of dynamic cerebral autoregulation (DCA). In contrast, CO2-vasomotor reactivity of the right middle cerebral artery was only slightly reduced. We therefore assume that the cerebral arteriolar dysfunction in eclampsia leads primarily to an impairment of the autoregulatory mechanism that is followed by different degrees of arteriolar vasodilation. Because of its probably high sensitivity to hemodynamic disturbances, assessment of DCA might be of great value in early pre-eclampsia for risk prediction of cerebral arteriopathy and eclampsia. [ABSTRACT FROM AUTHOR]

Arterial blood pressure (ABP) shows polyphasic changes during the Mueller manoeuvre (voluntary negative intrathoracic pressure). The aim of the present study was to investigate (1) whether these changes could be applied to detect impaired dynamic cerebral autoregulation (dCA) in carotid stenosis and (2) whether the degree of indicated impairment correlates with transfer function phase as another current measure for dCA (deep breathing method) and CO2-reactivity. We examined 13 patients with severe unilateral carotid artery stenosis and 16 age-matched controls during 15-s Mueller manoeuvres (MM) at -30 mmHg using bilateral transcranial Doppler sonography and non-invasive ABP recordings (Finapres, 2300, Ohmeda, Englewood, CO, USA). After an initial biphasic oscillation, cerebral blood flow velocity (CBFV) and ABP decreased to below baseline. CBFV reincreased in controls and on contralateral sides in patients 6·0 s (3·8–9·5 s, median and range) after the onset of the decrease, despite a further fall in ABP. CBFV over the affected side revealed a significantly delayed reincrease (8·0 (5·6–10·3) s; P<0·01) combined with a relatively flat and inertial amplitude behaviour. An applied autoregulation index derived from the MM (mROR), phase shift and CO2-reactivity were severely reduced on the affected side in patients (P<0·01). Reduction of the mROR correlated significantly with reduction of phase shift (r=0·69; P=0·002) and CO2-reactivity (r=0·78; P=0·002). In conclusion, the different cerebral haemodynamic pattern during the MM in patients is likely to reflect impaired dCA. The degree of indicated impairment correlates with that of transfer function phase and CO2-reactivity. Therefore, the MM represents a convenient method for grading of compromised cerebral haemodynamics in patients with carotid artery stenosis. [ABSTRACT FROM AUTHOR]

Elevated cardiorespiratory fitness (CRF) is associated with reduced dynamic cerebral autoregulation (dCA), but the impact of exercise training per se on dCA remains equivocal. In addition, resting cerebral blood flow (CBF) and dCA after high‐intensity interval training (HIIT) in individuals with already high CRF remains unknown. We examined to what extent 6 weeks of HIIT affect resting CBF and dCA in cardiorespiratory fit men and explored if potential changes are intensity‐dependent. Endurance‐trained men were assigned to group HIIT85 (85% of maximal aerobic power, 1–7 min effort bouts, n = 8) and HIIT115 (115% of maximal aerobic power, 30 sec to 1 min effort bouts, n = 9). Training sessions were completed until exhaustion 3 times/week over 6 weeks. Mean arterial pressure (MAP) and middle cerebral artery mean blood velocity (MCAvmean) were measured continuously at rest and during repeated squat‐stands (0.05 and 0.10 Hz). Transfer function analysis (TFA) was used to characterize dCA on driven blood pressure oscillations during repeated squat‐stands. Neither training nor intensity had an effect on resting MAP and MCAvmean (both P > 0.05). TFA phase during 0.10 Hz squat‐stands decreased after HIIT irrespective of intensity (HIIT85: 0.77 ± 0.22 vs. 0.67 ± 0.18 radians; HIIT115: pre: 0.62 ± 0.19 vs. post: 0.59 ± 0.13 radians, time effect P = 0.048). These results suggest that HIIT over 6 weeks have no apparent benefits on resting CBF, but a subtle attenuation in dCA is seen posttraining irrespective of intensity training in endurance‐trained men. [ABSTRACT FROM AUTHOR]