Two paths to one destination: altered low-frequency oscillations of cerebral perfusion and oxygenation but not oxygen metabolism in mild cognitive impairment.

Cerebrovascular dysfunction, a risk factor for dementia, is challenging to detect in mild cognitive impairment (MCI). Herein, we used novel, light-based technology to investigate low-frequency hemodynamic oscillations (LFOs; 0.02-0.

Blood pressure in human large cerebral arteries: a feasibility study.

The lack of direct measures of brain blood pressure (BBP) has severely restricted understanding of cerebral pressure-flow relationships and their control. We sought to evaluate the feasibility of directly measuring BBP and its pulsatility between the aorta and middle cerebral artery (MCA) during elective endovascular surgical procedures. We report five case studies (four female, 61 ± 13 yr; means ± SD) of patients undergoing cerebrovascular interventional procedures for aneurysm and stenoses, using direct BBP measures with the COMET 2 pressure guidewire system (Boston Scientific).

Cerebrovascular compliance during progressive hypotension in patients with autonomic failure.

The compliant nature of cerebral blood vessels may represent an important mechanical protection for sustained cerebral perfusion during reductions in arterial blood pressure (ABP). However, whether the rise in cerebrovascular compliance (Ci) with falling ABP persists and exhibits a threshold effect remains unknown. Therefore, we analyzed Ci changes during graded head-up tilt (HUT) in individuals with autonomic failure (AF), a group that tolerates graded and progressive reductions in ABP.

Short-term estradiol administration does not restore endothelin-B receptor-mediated vasodilation in postmenopausal women.

The endothelin-B receptor (ETR) mediates vasodilation in young women, an effect that is absent in postmenopausal women. We have previously demonstrated that ETR-mediated vasodilation is regulated by estradiol (E) in young women; however, the impact of E on ETR function in postmenopausal women remains unknown. Accordingly, the objective of this study was to test the hypothesis that E exposure restores ETR-mediated dilation in postmenopausal women.

Effect of insulin on indices of cerebral blood flow and cerebrovascular compliance in young adults.

Insulin has important vasodilatory effects in the peripheral circulation, but less is known about insulin's role in cerebrovascular control. Herein, we hypothesized both systemic (intravenous) and local (intranasal) insulin administration would increase indices of cerebral blood flow and reduce cerebrovascular compliance (Ci) in young adults. Participants were assigned to one of four separate protocols.

All-optics technique for monitoring absolute cerebral blood flow: validation against magnetic resonance imaging perfusion.

Significance: The ability to monitor cerebral blood flow (CBF) at the bedside is essential to managing critical-care patients with neurological emergencies. Diffuse correlation spectroscopy (DCS) is ideal because it is non-invasive, portable, and inexpensive. We investigated a near-infrared spectroscopy (NIRS) approach for converting DCS measurements into physiological units of blood flow.

Rapid changes in cerebrovascular compliance during vasovagal syncope.

Purpose: The compensatory mechanisms supporting cerebral perfusion throughout head-up tilt (HUT) in patients with vasovagal syncope (VVS) remain unclear. We tested the hypothesis that increased cerebrovascular compliance (Ci) and decreased cerebrovascular resistance (CVR) support cerebral blood velocity (CBV) during pre-syncope in VVS.

Methods: Finger arterial blood pressure (ABP) and right middle cerebral artery blood velocity (CBV) were recorded in 15 individuals diagnosed with VVS (n = 11 female, mean age: 40 ± 16 years, mean body mass index: 24.

Assessing changes in regional cerebral hemodynamics in adults with a high-density full-head coverage time-resolved near-infrared spectroscopy device.

Significance: Cerebral oximeters have the potential to detect abnormal cerebral blood oxygenation to allow for early intervention. However, current commercial systems have two major limitations: (1) spatial coverage of only the frontal region, assuming that surgery-related hemodynamic effects are global and (2) susceptibility to extracerebral signal contamination inherent to continuous-wave near-infrared spectroscopy (NIRS).

Aim: This work aimed to assess the feasibility of a high-density, time-resolved (tr) NIRS device (Kernel Flow) to monitor regional oxygenation changes across the cerebral cortex during surgery.

Characterization of cerebral macro- and microvascular hemodynamics during transient hypotension.

The aim of the current study was to establish the interplay between blood flow patterns within a large cerebral artery and a downstream microvascular segment under conditions of transiently reduced mean arterial pressure (MAP). We report data from nine young, healthy participants (5 women; 26 ± 4 yr) acquired during a 15-s bout of sudden-onset lower body negative pressure (LBNP; -80 mmHg). Simultaneous changes in microvascular cerebral blood flow (CBF) and middle cerebral artery blood velocity (MCAv) were captured using diffuse correlation spectroscopy (DCS) and transcranial Doppler ultrasound (TCD), respectively.

Using depth-enhanced diffuse correlation spectroscopy and near-infrared spectroscopy to isolate cerebral hemodynamics during transient hypotension.

Significance: Combining diffuse correlation spectroscopy (DCS) and near-infrared spectroscopy (NIRS) permits simultaneous monitoring of multiple cerebral hemodynamic parameters related to cerebral autoregulation; however, interpreting these optical measurements can be confounded by signal contamination from extracerebral tissue.

Aim: We aimed to evaluate extracerebral signal contamination in NIRS/DCS data acquired during transient hypotension and assess suitable means of separating scalp and brain signals.

Approach: A hybrid time-resolved NIRS/multidistance DCS system was used to simultaneously acquire cerebral oxygenation and blood flow data during transient orthostatic hypotension induced by rapid-onset lower body negative pressure (LBNP) in nine young, healthy adults.

Assessing the Sensitivity of Multi-Distance Hyperspectral NIRS to Changes in the Oxidation State of Cytochrome C Oxidase in the Brain.

Near-infrared spectroscopy (NIRS) measurements of tissue oxygen saturation (StO) are frequently used during vascular and cardiac surgeries as a non-invasive means of assessing brain health; however, signal contamination from extracerebral tissues remains a concern. As an alternative, hyperspectral (hs)NIRS can be used to measure changes in the oxidation state of cytochrome c oxidase (ΔoxCCO), which provides greater sensitivity to the brain given its higher mitochondrial concentration versus the scalp. The purpose of this study was to evaluate the depth sensitivity of the oxCCO signal to changes occurring in the brain and extracerebral tissue components.

Assessing the relationship between the cerebral metabolic rate of oxygen and the oxidation state of cytochrome-c-oxidase.

Hyperspectral near-infrared spectroscopy (hsNIRS) combined with diffuse correlation spectroscopy (DCS) provides a noninvasive approach for monitoring cerebral blood flow (CBF), the cerebral metabolic rate of oxygen ( ) and the oxidation state of cytochrome-c-oxidase (oxCCO). is calculated by combining tissue oxygen saturation ( ) with CBF, whereas oxCCO can be measured directly by hsNIRS. Although both reflect oxygen metabolism, a direct comparison has yet to be studied.

ET receptor-mediated vasodilation is regulated by estradiol in young women.

The endothelin-B (ET) receptor is a key regulator of vascular endothelial function in women. We have previously shown that the ET receptor mediates vasodilation in young women, an effect that is lost after menopause. However, the direct impact of changes in estradiol (E) on ET receptor function in women remains unclear.

Altered endothelial ET receptor expression in postmenopausal women.

The endothelin system plays an important role in mediating vascular function. The endothelin-B receptor (ETR) on endothelial cells mediates vasodilation via nitric oxide production. The vasodilatory effect of the ETR is lost following menopause and may contribute to impaired vascular endothelial function in postmenopausal women (PMW).

Acute exercise-related cognitive effects are not attributable to changes in end-tidal CO or cerebral blood velocity.

Purpose: Cognition, cerebral blood flow (CBF) and its major regulator (i.e., arterial CO), increase with submaximal exercise and decline with severe exercise.

Swimming-related effects on cerebrovascular and cognitive function.

Both acute and regular exercise influence vascular and cognitive function. Upright aquatic exercise increases mean middle cerebral artery blood velocity (MCAv ) and has been suggested as favorable for cerebrovascular adaptations. However, MCAv has not been reported during swimming.

Cerebrovascular regulation is not blunted during mental stress.

New Findings: What is the central question of the study? What are the effects of acute mental stress on the mechanisms regulating cerebral blood flow? What is the main finding and its importance? The major new findings are as follows: (i) high mental stress and hypercapnia had an interactive effect on mean middle cerebral artery blood velocity; (ii) high mental stress altered the regulation of cerebral blood flow; (iii) the increased cerebrovascular hypercapnic reactivity was not driven by changes in mean arterial pressure alone; and (iv) this increased perfusion with mental stress appeared not to be justified functionally by an increase in oxygen demand (as determined by near-infrared spectroscopy-derived measures).

Abstract: In this study, we examined the effects of acute mental stress on cerebrovascular function. Sixteen participants (aged 23 ± 4 years; five female) were exposed to low and high mental stress using simple arithmetic (counting backwards from 1000) and more complex arithmetic (serial subtraction of 13 from a rapidly changing four-digit number), respectively.

Reactivity of larger intracranial arteries using 7 T MRI in young adults.

The larger intracranial conduit vessels contribute to the total cerebral vascular resistance, and understanding their vasoreactivity to physiological stimuli is required when attempting to understand regional brain perfusion. Reactivity of the larger cerebral conduit arteries remains understudied due to a need for improved imaging methods to simultaneously assess these vessels in a single stimulus. We characterized reactivity of basal intracranial conduit arteries (basilar, right and left posterior, middle and anterior cerebral arteries) and the right and left internal carotid arteries, to manipulations in end-tidal CO (PetCO).

Ventilation inhibits sympathetic action potential recruitment even during severe chemoreflex stress.

This study investigated the influence of ventilation on sympathetic action potential (AP) discharge patterns during varying levels of high chemoreflex stress. In seven trained breath-hold divers (age 33 ± 12 yr), we measured muscle sympathetic nerve activity (MSNA) at baseline, during preparatory rebreathing (RBR), and during ) functional residual capacity apnea (FRC) and ) continued RBR. Data from RBR were analyzed at matched (i.