Vasomotion – what is currently thought?

Aalkjær, Christian; Boedtkjer, Donna Briggs; Matchkov, Vladimir V.

doi:10.1111/j.1748-1716.2011.02320.x

Cited by 208 publications

(238 citation statements)

References 203 publications

(317 reference statements)

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“…For example, vascular tone exhibits low-frequency oscillations in the absence of stimulus, known as vasomotion (Aalkjaer et al, 2011;Hudetz et al, 1998), although the phenomenon is still poorly understood. However, CBV-based resting-state fMRI with a superparamagnetic contrast agent has been performed on a rat model (Lu et al, 2007).…”

Section: Discussionmentioning

confidence: 99%

Detecting resting-state brain activity by spontaneous cerebral blood volume fluctuations using whole brain vascular space occupancy imaging

Miao

Yan³

et al. 2014

NeuroImage

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Resting-state brain activity has been investigated extensively using BOLD contrast. However, BOLD signal represents the combined effects of multiple physiological processes and its spatial localization is less accurate than that of cerebral blood flow and volume (CBF and CBF, respectively). In this study, we demonstrate that resting-state brain activity can be reliably detected by spontaneous fluctuations of CBV-weighted signal using whole-brain gradient and spin echo (GRASE) based vascular space occupancy (VASO) imaging. Specifically, using independent component analysis, intrinsic brain networks, including default mode, salience, executive control, visual, auditory, and sensorimotor networks were revealed robustly by the VASO technique. We further demonstrate that taskevoked VASO signal aligned well with expected gray matter areas, while blood-oxygenation level dependent (BOLD) signal extended outside of these areas probably due to their different spatial specificity. The improved spatial localization of VASO is consistent with previous studies using animal models. Moreover, we showed that the 3D-GRASE VASO images had reduced susceptibility-induced signal voiding, compared to the BOLD technique. This is attributed to the fact that VASO does not require T 2 * weighting, thus the acquisition can use a shorter TE and can employ spin-echo scheme. Consequently VASO-based functional connectivity signals were well preserved in brain regions that tend to suffer from signal loss and geometric distortion in BOLD, such as orbital prefrontal cortex. Our study suggests that 3D-GRASE VASO imaging, with its improved spatial specificity and less sensitivity to susceptibility artifacts, may have advantages in resting-state fMRI studies.Published by Elsevier Inc.

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Section: Discussionmentioning

confidence: 99%

Detecting resting-state brain activity by spontaneous cerebral blood volume fluctuations using whole brain vascular space occupancy imaging

Miao

Yan³

et al. 2014

NeuroImage

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“…An in vivo model is preferred to understand testicular physiology, as there are autoprotective mechanisms against low O 2 tension in the testis (Elshaari et al 2012) and natural antioxidant systems (Aitken and Roman 2008;Reyes et al 2012) that are difficult or impossible to replicate in an in vitro model. Furthermore, under heat stress, testicular vasomotion (rhythmic tone variation in blood vessels) is greatly suppressed (Setchell et al 1995) which can impair testicular function (Lysiak et al 2000;Aalkjaer et al 2011). …”

Section: Discussionmentioning

confidence: 99%

Hyperthermia and not hypoxia may reduce sperm motility and morphology following testicular hyperthermia

Kastelic¹,

Wilde²,

Rizzoto³

et al. 2017

Vet. Med.

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ABSTRACT:The mammalian testis typically operates on the brink of hypoxia; the long-standing dogma is that increased testicular temperature increases metabolism, but blood flow is unaffected and the resulting hypoxia reduces sperm motility and morphology. In rats and mice, oxygen (O 2 ) content of inspired air affected O 2 content of testes, enabling the latter to range from approximately 50 to more than 200% of physiologic concentrations. A ram model was used to test the hypotheses that hypoxia would disrupt sperm motility and morphology and that hyperoxia would prevent hyperthermia-induced reductions in sperm motility and morphology. Eighteen Canadian Arcott rams (approximately 10 months old) were used in a 2 × 3 factorial, with factors being scrotal insulation (insulated or not insulated) and O 2 concentrations in inspired air (14, 21 or 85%). Six rams, three with and three without scrotal insulation, were placed in each of three enclosed areas for 30 h to expose them to their respective oxygen concentrations, with scrotal insulation removed at the end of the exposure. Semen was collected by electro-ejaculation twice before insulation, bi-weekly for four weeks starting one week after exposures, and then once weekly for two weeks. There were effects of insulation, time and an insulation × time interaction for motile sperm and sperm that had normal morphology or head or midpiece defects (P < 0.01 for each). Sperm motility and morphology exhibited alterations between approximately two and five weeks after insulation, with mean progressively motile and morphologically normal sperm decreasing from approximately 55 to 35% and from 80 to 30%, respectively, and with head and midpiece defects increasing from approximately 3 to 50% and from 10 to 20% (P < 0.05 for each). The hypotheses that hypoxia would disrupt sperm quality and production, whereas hyperoxia would prevent hyperthermia-induced reductions in sperm quality and production, were not supported. This is apparently the first report that heat-stress induced damage to sperm was due to increased temperature per se and not testicular hypoxia, calling into question a long-standing paradigm.

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“…However, substantial evidence suggests that at least a portion of the LFOs seen in brain imaging studies is nonneuronal and may arise in part from the influence of instrumental noise and aliasing artifacts from undersampled cardiac and respiratory fluctuations, due to the low sampling rate in fMRI studies. 8,10 Other low-frequency physiological sources of these LFO components may include vasomotion from oscillations in the vascular tone thought to be generated within the vessel walls 5,11 or variations in respiratory volume and cardiac rate resulting from systemic modulation of cerebral blood flow.…”

Section: Introductionmentioning

confidence: 99%

Low-frequency oscillations measured in the periphery with near-infrared spectroscopy are strongly correlated with blood oxygen level-dependent functional magnetic resonance imaging signals

et al. 2012

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Abstract. Low-frequency oscillations (LFOs) in the range of 0.01-0.15 Hz are commonly observed in functional imaging studies, such as blood oxygen level-dependent functional magnetic resonance imaging (BOLD fMRI) and functional near-infrared spectroscopy (fNIRS). Some of these LFOs are nonneuronal and are closely related to autonomic physiological processes. In the current study, we conducted a concurrent resting-state fMRI and NIRS experiment with healthy volunteers. LFO data was collected simultaneously at peripheral sites (middle fingertip and big toes) by NIRS, and centrally in the brain by BOLD fMRI. The cross-correlations of the LFOs collected from the finger, toes, and brain were calculated. Our data show that the LFOs measured in the periphery (NIRS signals) and in the brain (BOLD fMRI) were strongly correlated with varying time delays. This demonstrates that some portion of the LFOs actually reflect systemic physiological circulatory effects. Furthermore, we demonstrated that NIRS is effective for measuring the peripheral LFOs, and that these LFOs and the temporal shifts between them are consistent in healthy participants and may serve as useful biomarkers for detecting and monitoring circulatory dysfunction.

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Vasomotion – what is currently thought?

Cited by 208 publications

References 203 publications

Detecting resting-state brain activity by spontaneous cerebral blood volume fluctuations using whole brain vascular space occupancy imaging

Detecting resting-state brain activity by spontaneous cerebral blood volume fluctuations using whole brain vascular space occupancy imaging

Hyperthermia and not hypoxia may reduce sperm motility and morphology following testicular hyperthermia

Low-frequency oscillations measured in the periphery with near-infrared spectroscopy are strongly correlated with blood oxygen level-dependent functional magnetic resonance imaging signals

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