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Portable and Rapid <i>In Vivo</i> Imaging of Tissue Oxygenation Changes Induced by Skin Perfusion Pressure. JOURNAL OF BIOMIMETICS BIOMATERIALS AND BIOMEDICAL ENGINEERING 2019. [DOI: 10.4028/www.scientific.net/jbbbe.42.59] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Current imaging systems available in the study of tissue hemodynamics and vascular reactivity are typically complex and bulky, hence limiting their applications to laboratory use. The aim of this study is to present the dynamics of skin oxygen level with changes in the microcirculatory perfusion monitored using a developed field portable, handheld tri-wavelength imaging system. The skin oxygen saturation level (StO2) was measured in-vivo in a span of 12 minutes in the ventral forearm of seven healthy humans at rest, before and after supra-diastolic and supra-systolic pressure inflations. The findings of this work showed statistical significance in the difference between the mean StO2 values in baseline and that following ischemic episodes with ρ ≤ 0.03. The values returned to baseline, although of different magnitude for each individual, within 2 min (ρ =0.217) during reperfusion could suggest the time required for the resume of normal autoregulation mechanisms and vasomotion reactivities in the recruits. This study concluded that the developed imaging system could find potential application in self-healthcare management and may help to improve patient care in remote or rural locations.
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Abstract
OBJECTIVES Connectionist theories of brain function took hold with the seminal contributions of Norman Geschwind a half century ago. Modern neuroimaging techniques have expanded the scientific interest in the study of brain connectivity to include the intact as well as disordered brain. METHODS In this review, we describe the most common techniques used to measure functional and structural connectivity, including resting state functional MRI, diffusion MRI, and electroencephalography and magnetoencephalography coherence. We also review the most common analytical approaches used for examining brain interconnectivity associated with these various imaging methods. RESULTS This review presents a critical analysis of the assumptions, as well as methodological limitations, of each imaging and analysis approach. CONCLUSIONS The overall goal of this review is to provide the reader with an introduction to evaluating the scientific methods underlying investigations that probe the human connectome.
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Savelov AA, Petrovskii ED, Karamamed-Ogly ES, Shtark MB. Functions of the hemodynamic response during hypercapnia. Functional MRI study. Bull Exp Biol Med 2013; 155:1-5. [PMID: 23667858 DOI: 10.1007/s10517-013-2065-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Functional MRI was applied for studying the dynamics of brain hemodynamic response evoked by involuntary (visual) and voluntary (motor) excitations under condition of interdependent sensorimotor and visual paradigm (hand clenching in response to a light flash). Activation of the corresponding areas of the visual and sensorimotor cortex (Brodmann areas 18-4, respectively) was observed and quantitative data characterizing the response signal maximum delay were obtained. It was found that breath holding-induced hypercapnia disorders neuronal networks created during visual-motor stimulation.
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Affiliation(s)
- A A Savelov
- International Tomography Center, Siberian Division of the Russian Academy of Sciences, Novosibirsk, Russia.
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Panerai RB, Dineen NE, Brodie FG, Robinson TG. Spontaneous fluctuations in cerebral blood flow regulation: contribution of PaCO2. J Appl Physiol (1985) 2010; 109:1860-8. [DOI: 10.1152/japplphysiol.00857.2010] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
To investigate the temporal variability of dynamic cerebral autoregulation (CA), the transient response of cerebral blood flow to rapid changes in arterial blood pressure, a new approach was introduced to improve the temporal resolution of dynamic CA assessment. Continuous bilateral recordings of cerebral blood flow velocity (transcranial Doppler, middle cerebral artery), end-tidal Pco2 (PetCO2, infrared capnograph), and blood pressure (Finapres) were obtained at rest and during breath hold in 30 young subjects (25 ± 6 yr old) and 30 older subjects (64 ± 4 yr old). Time-varying estimates of the autoregulation index [ARI( t)] were obtained with an autoregressive-moving average model with coefficients expanded by orthogonal decomposition. The temporal pattern of ARI( t) varied inversely with PetCO2, decreasing with hypercapnia. At rest, ARI( t) showed spontaneous fluctuations that were significantly different from noise and significantly correlated with spontaneous fluctuations in PetCO2 in the majority of recordings (young: 72% and old: 65%). No significant differences were found in ARI( t) due to aging. This new approach to improve the temporal resolution of dynamic CA parameters allows the identification of physiologically meaningful fluctuations in dynamic CA efficiency at rest and in response to changes in arterial CO2.
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Affiliation(s)
- R. B. Panerai
- Medical Physics Group and
- Leicester National Institute of Health Research Biomedical Research Unit in Cardiovascular Science, Glenfield Hospital, Leicester, United Kingdom
| | - N. E. Dineen
- Ageing and Stroke Medicine Group, Department of Cardiovascular Sciences, University of Leicester National Health Service Trust, Leicester; and
| | - F. G. Brodie
- Ageing and Stroke Medicine Group, Department of Cardiovascular Sciences, University of Leicester National Health Service Trust, Leicester; and
| | - T. G. Robinson
- Ageing and Stroke Medicine Group, Department of Cardiovascular Sciences, University of Leicester National Health Service Trust, Leicester; and
- Leicester National Institute of Health Research Biomedical Research Unit in Cardiovascular Science, Glenfield Hospital, Leicester, United Kingdom
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Slow vasogenic fluctuations of intracranial pressure and cerebral near infrared spectroscopy--an observational study. Acta Neurochir (Wien) 2010; 152:1763-9. [PMID: 20700750 DOI: 10.1007/s00701-010-0748-9] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2010] [Accepted: 07/12/2010] [Indexed: 11/27/2022]
Abstract
BACKGROUND/PURPOSE Increased slow-wave activity in intracranial pressure (ICP) signifies an exhausted cerebrospinal compensatory reserve across a range of conditions. In this study, we attempted to describe synchronisation between slow waves of ICP and of near-infrared spectroscopy (NIRS) variables during controlled elevation of ICP. METHOD Nineteen patients presenting with symptomatic hydrocephalus underwent a Computerised Infusion Test. NIRS-derived indices, ICP and arterial blood pressure (ABP) were recorded simultaneously. FINDINGS ICP increased from 9.3 (6.0) mmHg to a 17.1 (8.9) mmHg during infusion. Slow waves in ICP were accompanied by concurrent waves in each NIRS variable (including deoxygenated haemoglobin (Hb) and oxygenated haemoglobin (HbO2)) with a mean coherence of >0.7 and no significant phase shift. In the same bandwidth (0.3-1.8 min(-1)), ABP fluctuations occurred with a coherence of 0.77 and phase lead of 40° with respect to ICP. The power of ICP slow waves increased significantly during infusion plateau with a corresponding increase in power of Hb waves. CONCLUSIONS Slow fluctuations in cerebral oximetry as detected by NIRS coincide with and are implicated in the origin of ICP slow waves and increases during periods of exhausted cerebrospinal compensatory reserve. NIRS may be used as a non-invasive marker of increased ICP slow waves (and therefore reduced CSF compensatory reserve).
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Dineen NE, Brodie FG, Robinson TG, Panerai RB. Continuous estimates of dynamic cerebral autoregulation during transient hypocapnia and hypercapnia. J Appl Physiol (1985) 2009; 108:604-13. [PMID: 20035062 DOI: 10.1152/japplphysiol.01157.2009] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Dynamic cerebral autoregulation (CA) is the transient response of cerebral blood flow (CBF) to rapid blood pressure changes: it improves in hypocapnia and becomes impaired during hypercapnia. Batch-processing techniques have mostly been used to measure CA, providing a single estimate for an entire recording. A new approach to increase the temporal resolution of dynamic CA parameters was applied to transient hypercapnia and hypocapnia to describe the time-varying properties of dynamic CA during these conditions. Thirty healthy subjects (mean +/- SD: 25 +/- 6 yr, 9 men) were recruited. CBF velocity was recorded in both middle cerebral arteries (MCAs) with transcranial Doppler ultrasound. Arterial blood pressure (Finapres), end-tidal CO(2) (ET(CO(2)); infrared capnograph), and a three-lead ECG were also measured at rest and during repeated breath hold and hyperventilation. A moving window autoregressive moving average model provided continuous values of the dynamic CA index [autoregulation index (ARI)] and unconstrained gain. Breath hold led to significant increase in ET(CO(2)) (+5.4 +/- 6.1 mmHg), with concomitant increase in CBF velocity in both MCAs. Continuous dynamic CA parameters showed highly significant changes (P < 0.001), with a temporal pattern reflecting a delayed dynamic response of CA to changes in arterial Pco(2) and a maximal reduction in ARI of -5.1 +/- 2.4 and -5.1 +/- 2.3 for the right and left MCA, respectively. Hyperventilation led to a marked decrease in ET(CO(2)) (-7.2 +/- 4.1 mmHg, P < 0.001). Unexpectedly, CA efficiency dropped significantly with the inception of the metronome-controlled hyperventilation, but, after approximately 30 s, the ARI increased gradually to show a maximum change of 5.7 +/- 2.9 and 5.3 +/- 3.0 for the right and left MCA, respectively (P < 0.001). These results confirm the potential of continuous estimates of dynamic CA to improve our understanding of human cerebrovascular physiology and represent a promising new approach to improve the sensitivity of clinical applications of dynamic CA modeling.
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Affiliation(s)
- N E Dineen
- Ageing and Stroke Medicine Group, Department of Cardiovascular Sciences, University of Leicester, UK
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Biswal BB, Kannurpatti SS. Resting-state functional connectivity in animal models: modulations by exsanguination. Methods Mol Biol 2009; 489:255-74. [PMID: 18839096 PMCID: PMC10671844 DOI: 10.1007/978-1-59745-543-5_12] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2023]
Abstract
We studied the spatiotemporal characteristics of the resting state low frequency fluctuations in functional MRI (fMRI), blood oxygenation level dependent (BOLD) signal in isoflurane-anesthetized rats. fMRI-BOLD measurements at 9.4 Telsa were made during normal and exsanguinated condition previously known to alter cerebral blood flow (CBF) fluctuations in anesthetized rats. fMRI signal time series were low-pass filtered and studied by spectral analysis. During normal conditions, baseline mean arterial pressure (MAP) was 110 +/- 10 mm Hg and low-frequency fluctuations in BOLD signal were observed in the frequency range of 0.01 - 0.125 Hz. Following blood withdrawal (exsanguination), MAP decreased to 68 +/- 7 mm Hg, resulting in an increase in the amplitude of the low-frequency fluctuations in BOLD signal time series and an increase in power at several frequencies between 0.01 and 0.125 Hz. Spatially, the BOLD fluctuations were confined to the cortex and thalamus spanning both hemispheres with sparse presence in the caudate putamen and hippocampus during both normal and exsanguinated states. Spatial distribution of the low frequency fluctuations in BOLD signal, from cross correlation analysis, indicates substantial inter-hemispheric synchrony similar to that observed in the conscious human brain. The behavior of the resting state BOLD signal fluctuations similar to CBF fluctuations during exsanguination indicates a myogenic dependence. Also, a high inter-hemispheric synchrony combined with different phase characteristics of the low frequency BOLD fluctuations particularly in the hippocampus relative to the cortex emphasizes distinct functional networks.
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Affiliation(s)
- Bharat B Biswal
- Department of Radiology, UMDNJ-New Jersey Medical School, Newark, NJ, USA
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Kannurpatti SS, Biswal BB, Kim YR, Rosen BR. Spatio-temporal characteristics of low-frequency BOLD signal fluctuations in isoflurane-anesthetized rat brain. Neuroimage 2008; 40:1738-47. [PMID: 18339559 PMCID: PMC10671857 DOI: 10.1016/j.neuroimage.2007.05.061] [Citation(s) in RCA: 95] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2006] [Revised: 05/10/2007] [Accepted: 05/29/2007] [Indexed: 11/20/2022] Open
Abstract
We studied the spatio-temporal characteristics of the resting state low-frequency fluctuations in fMRI-BOLD signal in isoflurane-anesthetized rats. fMRI-BOLD measurements at 9.4 T were made during normal and exsanguinated condition previously known to alter cerebral blood flow (CBF) fluctuations in anesthetized rats. fMRI signal time series were low pass filtered and studied by spectral analysis. During normal conditions, baseline mean arterial pressure (MAP) was 110+/-10 mm Hg and low-frequency fluctuations in BOLD signal were observed in the frequency range of 0.01 to 0.125 Hz. Following blood withdrawal (exsanguination), MAP decreased to 68+/-7 mm Hg, resulting in an increase in the amplitude of the low-frequency fluctuations in BOLD signal time series and an increase in power at several frequencies between 0.01 and 0.125 Hz. Spatially, the BOLD fluctuations were confined to the cortex and thalamus spanning both hemispheres with sparse presence in the caudate putamen and hippocampus during both normal and exsanguinated states. Spatial distribution of the low-frequency fluctuations in BOLD signal, from cross-correlation analysis, indicates substantial inter-hemispheric synchrony similar to that observed in the conscious human brain. The behavior of the resting state BOLD signal fluctuations similar to CBF fluctuations during exsanguination indicates a myogenic dependence. Also, a high inter-hemispheric synchrony combined with different phase characteristics of the low-frequency BOLD fluctuations particularly in the hippocampus relative to the cortex emphasizes distinct functional networks.
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Affiliation(s)
- Sridhar S. Kannurpatti
- Department of Radiology, UMDNJ-New Jersey Medical School, ADMC Bldg-5, Suite 575, 30 Bergen Street, Newark, NJ 07103, USA
| | - Bharat B. Biswal
- Department of Radiology, UMDNJ-New Jersey Medical School, ADMC Bldg-5, Suite 575, 30 Bergen Street, Newark, NJ 07103, USA
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Panerai RB, Carey BJ, Potter JF. Short-term variability of cerebral blood flow velocity responses to arterial blood pressure transients. ULTRASOUND IN MEDICINE & BIOLOGY 2003; 29:31-38. [PMID: 12604115 DOI: 10.1016/s0301-5629(02)00698-1] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The time course of mean beat-to-beat changes in cerebral blood flow velocity changes induced by spontaneous transients in mean arterial blood pressure was studied in a group of 39 healthy subjects, ages 40 +/- 15 (SD) years. Continuous 10-min noninvasive recordings of cerebral blood flow velocity (CBFV) from both middle cerebral arteries (MCA) with Doppler ultrasound (US) and simultaneous beat-to-beat arterial blood pressure (ABP) were made. A total of 522 spontaneous positive transients of ABP and CBFV were extracted with a maximum of 15 transients for each subject. The CBFV transient amplitude was normalized by the corresponding ABP change and the area-under-the-curve (AUC) of the falling phase was used to classify the CBFV regulatory response as either weak, moderate or strong. The coherent average of ABP and CBFV of each category confirmed the consistency of this classification, reinforced by the agreement of separate averages for recordings from the right and left MCA. All 39 subjects showed at least two categories of transients, with all three categories present in 33 subjects (right MCA) and 29 subjects (left MCA), respectively. These results indicate a significant short-term variability of CBFV responses in healthy subjects whose origin remains unexplained.
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Affiliation(s)
- Ronney B Panerai
- Division of Medical Physics, University of Leicester, Leicester Royal Infirmary, Leicester, UK.
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Li SJ, Li Z, Wu G, Zhang MJ, Franczak M, Antuono PG. Alzheimer Disease: evaluation of a functional MR imaging index as a marker. Radiology 2002; 225:253-9. [PMID: 12355013 DOI: 10.1148/radiol.2251011301] [Citation(s) in RCA: 224] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
PURPOSE To measure changes in functional synchrony in the hippocampus in patients with mild cognitive impairment (MCI) and Alzheimer disease (AD). MATERIALS AND METHODS Three subject groups (nine cognitively healthy elderly control subjects, 10 patients with probable AD, and five subjects with MCI) underwent resting-state functional magnetic resonance (MR) imaging for measurement of functional synchrony in the hippocampus. Functional synchrony was defined and quantified as the mean of the cross-correlation coefficients of spontaneous low frequency (COSLOF) components between possible pairs of voxel time courses in a brain region, or the COSLOF index. The two-tailed Student t test was used to determine differences in the COSLOF index between the control group, the probable AD group, and the MCI group. An operating characteristic curve was calculated to graphically depict the tradeoff between sensitivity and specificity of the COSLOF index. RESULTS Functional synchrony quantified with the COSLOF index was obtained in AD, MCI, and control subjects. COSLOF index values were significantly lower in AD patients than in control subjects (t = 4.32, P <.0012). For MCI subjects, COSLOF index values were significantly higher than those of AD patients (t = -2.4052, P <.047) but significantly lower than those of control subjects (t = 2.257, P <.043). The exponential-class curve significantly fits the relationship between the COSLOF index and the Mini-Mental Status Examination score (chi(2) = 20.4), indicating the rapid decrease in cognitive capacity below a threshold of the COSLOF index. CONCLUSION Our results suggest that the COSLOF index could be used as a noninvasive quantitative marker for the preclinical stage of AD.
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Affiliation(s)
- Shi-Jiang Li
- Biophysics Research Institute, Medical College of Wisconsin, 8701 Watertown Plank Rd, Milwaukee, WI 53226,USA.
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Lowe MJ, Phillips MD, Lurito JT, Mattson D, Dzemidzic M, Mathews VP. Multiple sclerosis: low-frequency temporal blood oxygen level-dependent fluctuations indicate reduced functional connectivity initial results. Radiology 2002; 224:184-92. [PMID: 12091681 DOI: 10.1148/radiol.2241011005] [Citation(s) in RCA: 216] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
PURPOSE To study the correlation of low-frequency blood oxygenation level-dependent (BOLD) fluctuations on magnetic resonance (MR) images obtained of the left- and right-hemisphere primary motor regions in healthy control subjects and patients with multiple sclerosis (MS). MATERIALS AND METHODS Sixteen healthy volunteers and 20 patients with MS underwent MR imaging with a 1.5-T imager by using a protocol designed to monitor low-frequency BOLD fluctuations. Data for low-frequency BOLD fluctuations were acquired with subjects at rest and during continuous performance of a bilateral finger-tapping task. These data were low-pass filtered (<0.08 Hz), and cross correlations of all acquired pixels to a region of interest in the left precentral gyrus were calculated. Confidence levels were calculated from the cross correlations. The fraction of pixels in the right precentral gyrus above a confidence level of 95% for correlation with the left precentral gyrus was calculated for each subject. RESULTS A plot of the fraction of the right precentral gyrus with high correlation with the left precentral gyrus for the finger-tapping state versus the resting state showed a clear discrimination between patients with MS and control subjects. Compared with control subjects, patients with MS generally had a smaller fraction of the pixels in the right precentral gyrus above the confidence level. This finding indicates that our method results in greater than 60% sensitivity and 100% specificity for discriminating patients with MS from control subjects. No significant correlation was found between clinical measures of MS disease and correlations of low-frequency BOLD fluctuations between left and right precentral gyri. CONCLUSION On the basis of the connectivity measure of low-frequency BOLD fluctuations, patients with MS exhibited lower functional connectivity between right- and left-hemisphere primary motor cortices when compared with that in control subjects.
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Affiliation(s)
- Mark J Lowe
- Department of Radiology, Indiana University School of Medicine, CL 157, 541 Clinical Dr, Indianapolis, IN 46202-5111, USA.
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Kiviniemi V, Jauhiainen J, Tervonen O, Pääkkö E, Oikarinen J, Vainionpää V, Rantala H, Biswal B. Slow vasomotor fluctuation in fMRI of anesthetized child brain. Magn Reson Med 2000; 44:373-8. [PMID: 10975887 DOI: 10.1002/1522-2594(200009)44:3<373::aid-mrm5>3.0.co;2-p] [Citation(s) in RCA: 136] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Signal intensity changes in fMRI during rest caused by vasomotor fluctuations were investigated in this work. Resting-state baseline fluctuations were evaluated in 12 children anesthetized with thiopental. Five subjects had fluctuations related to subvoxel motion. In seven subjects without significant motion, slow signal fluctuation at 0.025-0.041 Hz near one or more primary sensory cortices was observed. In each subject the amplitude and frequency of the fluctuations were stable. It is hypothesized that thiopental, which reduces blood pressure and flow in the cortex, alters the feedback in neurovascular coupling leading to an increase in the magnitude and a reduction in the frequency of these fluctuations. The use of anesthesia in fMRI may provide new insight into neural connectivity and the coupling of blood flow and neural metabolism.
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Affiliation(s)
- V Kiviniemi
- Department of Diagnostic Radiology, Oulu University Hospital, Oulu, Finland.
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Abstract
Tissue PO2 was measured in the primary visual cortex of anesthetized, artificially ventilated normovolemic cats to examine tissue oxygenation with respect to depth. The method utilized 1) a chamber designed to maintain cerebrospinal fluid pressure and prevent ambient PO2 from influencing the brain, 2) a microelectrode capable of recording electrical activity as well as local PO2, and 3) recordings primarily during electrode withdrawal from the cortex rather than during penetrations. Local peaks in the PO2 profiles were consistent with the presence of numerous vessels. Excluding the superficial 200 microm of the cortex, in which the ambient PO2 may have influenced tissue PO2, there was a slight decrease (4.9 Torr/mm cortex) in PO2 as a function of depth. After all depths and cats were weighted equally, the average PO2 in six cats was 12.8 Torr, with approximately one-half of the values being </=10 Torr. The kurtosis of the PO2 histogram, with all depths and cats weighted equally, was 3.61, and the skewness was 1.70.
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Affiliation(s)
- L B Padnick
- Department of Biomedical Engineering, Northwestern University, Evanston, Illinois 60208-3107, USA
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Haughton V, Biswal B. Clinical application of basal regional cerebral blood flow fluctuation measurements by FMRI. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1999; 454:583-90. [PMID: 9889938 DOI: 10.1007/978-1-4615-4863-8_69] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/09/2023]
Affiliation(s)
- V Haughton
- Department of Radiology, Medical College of Wisconsin, Milwaukee, USA
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Hudetz AG, Biswal BB, Shen H, Lauer KK, Kampine JP. Spontaneous fluctuations in cerebral oxygen supply. An introduction. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1999; 454:551-9. [PMID: 9889935 DOI: 10.1007/978-1-4615-4863-8_66] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Spontaneous, low frequency (4-12 cpm) fluctuations, independent of the cardiac and respiratory cycles, in human and animal brains were first recorded with the O2 polarographic technique in the late 1950s. They were seen in NADH and cytochrome oxidase and associated with spontaneous vasomotion pial and large cerebral arteries. Renewed interest in spontaneous fluctuations was generated by studies with laser-Doppler flowmetry (LDF), reflectance oximetry and functional MRI. Spontaneous fluctuations were consistently produced when cerebral perfusion was challenged by systemic or local manipulations; the fluctuation amplitude reached 30-40% of the mean. The most potent stimuli are hypotension, hyperventilation, cerebral artery occlusion and cerebral vasoconstriction elicited, for example, by a nitric oxide synthase inhibitor but not by indomethacin. The fluctuations are suspended by CO2 and halothane at concentrations that produce hyperemia. Recently, spontaneous fluctuations were recorded by LDF microprobes in areas as small as 130 microns and by video-microscopy in single capillaries. The fluctuations were absent in severe, focally ischemic brain territories. The dependence of spontaneous fluctuations on intravascular pressure argues for the importance of a myogenic mechanism, however, neuronal modulation may also play a role. Coherence of small vessel vasomotion may be required for the emergence of regional flow fluctuations. There is a need to elucidate the spatial and frequency domains in which fluctuations are present under normal physiological conditions and those in which they may reflect brain injury and pathologies of diagnostic or prognostic value.
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Affiliation(s)
- A G Hudetz
- Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, USA
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Elwell CE, Springett R, Hillman E, Delpy DT. Oscillations in Cerebral Haemodynamics. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1999. [DOI: 10.1007/978-1-4615-4717-4_8] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/11/2023]
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Biswal BB, Van Kylen J, Hyde JS. Simultaneous assessment of flow and BOLD signals in resting-state functional connectivity maps. NMR IN BIOMEDICINE 1997; 10:165-70. [PMID: 9430343 DOI: 10.1002/(sici)1099-1492(199706/08)10:4/5<165::aid-nbm454>3.0.co;2-7] [Citation(s) in RCA: 431] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
We have recently demonstrated using functional magnetic resonance imaging the presence of synchronous low-frequency fluctuations of signal intensities from the resting human brain that have a high degree of temporal correlation (p < 0.0001) both within and across the sensorimotor cortex. A statistically significant overlap between the resting-state functional connectivity map and the task-activation map due to bilateral finger tapping was obtained. Similar results have been obtained in the auditory and visual cortex. Because the pulse sequence used for collecting data was sensitive to blood flow and blood oxygenation, these low-frequency fluctuations of signal intensity may have arisen from variations of both. The objective of this study was simultaneously to determine the contribution of the blood oxygenation level signal and the flow signal to physiological fluctuations in the resting brain using the flow-sensitive alternating inversion recovery pulse sequence. In all subjects, the functional connectivity maps obtained from BOLD had a greater coincidence with task-activation maps than the corresponding functional connectivity maps obtained from blood-flow signals at the same level of statistical significance. Results of this study suggest that while variations in blood flow might contribute to functional connectivity maps, BOLD signals play a dominant role in the mechanism that gives rise to functional connectivity in the resting human brain.
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Affiliation(s)
- B B Biswal
- Biophysics Research Institute, Medical College of Wisconsin, Milwaukee 53226, USA
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Biswal B, Hudetz AG, Yetkin FZ, Haughton VM, Hyde JS. Hypercapnia reversibly suppresses low-frequency fluctuations in the human motor cortex during rest using echo-planar MRI. J Cereb Blood Flow Metab 1997; 17:301-8. [PMID: 9119903 DOI: 10.1097/00004647-199703000-00007] [Citation(s) in RCA: 130] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Using magnetic resonance (MR) echo-planar imaging (EPI), we recently demonstrated the presence of low-frequency fluctuations (< 0.1 Hz) in MR signal intensity from the resting human brain that have a high degree of temporal correlation (p < 10(-3)) within and across associated regions of the sensorimotor cortex. These fluctuations in MR signal intensity are believed to arise from fluctuations in capillary blood flow and oxygenation. A substantial overlap between the activation map generated by bilateral finger tapping and temporally-correlated voxels from the sensorimotor cortex obtained during rest was observed. In the work reported here, we investigated whether respiratory hypercapnia, which is known to suspend spontaneous oscillations in regional cerebral blood flow, influences these low-frequency fluctuations. The magnitude of low-frequency fluctuations was reversibly diminished during hypercapnia, resulting in a substantial decrease of the temporal correlation both within and across contralateral hemispheres of the sensorimotor cortex. After the breathing mixture was returned to ambient air, the magnitude and spatial extent of the temporal correlation of low-frequency fluctuations returned to normal. Results of this study support the hypothesis that low-frequency physiological fluctuations observed by MR in the human cortex and spontaneous flow oscillations observed in early studies by laser-Doppler flowmetry (LDF) in the cortex of the rat are identical and are secondary to fluctuations in neuronal activity.
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Affiliation(s)
- B Biswal
- Biophysics Research Institute, Medical College of Wisconsin, Milwaukee 53226-0509, USA
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Hoffman WE, Charbel FT, Edelman G, Ausman JI. Brain tissue gases and pH during arteriovenous malformation resection. Neurosurgery 1997; 40:294-300; discussion 300-1. [PMID: 9007861 DOI: 10.1097/00006123-199702000-00012] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
OBJECTIVE The purpose of this study was to determine whether baseline partial pressure of oxygen (PO2), partial carbon dioxide pressure (PCO2), and pH in brain tissue adjacent to arteriovenous malformations (AVMs) are different from those in control patients. In addition, PO2, PCO2, and pH changes were measured during resection of the AVMs. METHODS Two groups were studied. Group 1 (n = 8) was composed of nonischemic patients scheduled for cerebral aneurysm clipping. Group 2 (n = 13) was composed of patients undergoing neurosurgery for resection of AVMs. After the craniotomy, the dura was retracted and a combined PO2, PCO2, and pH sensor was inserted into nonischemic brain tissue in Group 1. In Group 2, the sensor was inserted into tissue 2 to 3 cm from the margin of the AVMs, within the same arterial blood supply. After equilibration of the sensor, tissue gases and pH were measured during steady-state anesthetic conditions in Group 1 and during resection of AVMs in Group 2. RESULTS Under baseline conditions before the start of surgery, tissue PO2 was decreased in patients with AVMs compared with control patients, but PCO2 and pH were not changed. During resection of the AVMs, PO2 and pH increased and PCO2 decreased compared with baseline measurements. These parameters did not change in control patients during a similar time period. CONCLUSION The results suggest that cerebrovascular or metabolic adaptation occurs in patients with AVMs with decreased tissue perfusion pressure as an adjustment for decreased oxygen delivery. During resection of AVMs, this adaptation produces a relative hyperemic environment with tissue hyperoxia, hypocapnia, and alkalosis that is not corrected by the end of surgery.
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Affiliation(s)
- W E Hoffman
- Department of Anesthesiology, University of Illinois at Chicago, USA
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Hoffman WE, Charbel FT, Edelman G, Abood C. Brain tissue response to CO2 in patients with arteriovenous malformation. J Cereb Blood Flow Metab 1996; 16:1383-6. [PMID: 8898716 DOI: 10.1097/00004647-199611000-00038] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
We tested whether cerebral arteriovenous malformations (AVM) alter brain tissue oxygen pressure, PO2, carbon dioxide pressure PCO2, and pH before, during, and after hypercapnia. A craniotomy was performed and a sensor inserted into normal brain tissue (control) (n = 7) or into tissue adjacent to an AVM (n = 9). Under baseline conditions, tissue PO2 was 80% lower in AVM compared to control patients, but PCO2 and pH were normal. During a 10 mm Hg increase in PaCO2, tissue PO2 increased only in AVM patients, PCO2 increased in both groups, and pH decreased only in controls. When hypercapnia was reversed, tissue PCO2 decreased below baseline and pH increased in AVM patients. Results suggest that tissue CO2 washout and elevated pH result from increases in blood flow during hypercapnia. This response may be related to symptoms of hyperperfusion during AVM resection.
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Affiliation(s)
- W E Hoffman
- Department of Anesthesiology, University of Illinois at Chicago, USA
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Hudetz AG, Roman RJ, Harder DR. Spontaneous flow oscillations in the cerebral cortex during acute changes in mean arterial pressure. J Cereb Blood Flow Metab 1992; 12:491-9. [PMID: 1569142 DOI: 10.1038/jcbfm.1992.67] [Citation(s) in RCA: 108] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The purpose of this study was to characterize spontaneous oscillations of blood flow in the cerebral cortex of anesthetized rats under control conditions and after mean arterial pressure was altered by various means. Blood flow was monitored using a laser-Doppler flowmeter through the closed cranium. Spontaneous flow oscillations with amplitudes of 14-30% of the mean flow and frequencies of 4-11 cycles/min were recorded when arterial pressures were less than 90 mm Hg. Stepwise hemorrhagic hypotension and unilateral carotid occlusion increased the amplitude of oscillations. The amplitude of oscillations was negatively correlated with the level of mean arterial pressure after manipulation with norepinephrine or sodium nitroprusside. The oscillations were reversibly abolished during dilation of the cerebral circulation by elevating the inspired carbon dioxide content to 5%. The frequency of flow oscillations was very stable during all of the above maneuvers except during the infusion of norepinephrine, which increased the oscillation frequency slightly. The results suggest that flow oscillations are determined primarily by cerebral arterial pressure.
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Affiliation(s)
- A G Hudetz
- Department of Physiology, Medical College of Wisconsin, Milwaukee 53226
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Wei DT, Saidel GM, Jones SC. Optimal design of a thermistor probe for surface measurement of cerebral blood flow. IEEE Trans Biomed Eng 1990; 37:1159-72. [PMID: 2289790 DOI: 10.1109/10.64457] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Microthermistors are put on the surface of cerebral cortex to monitor local cerebral blood flow (CBF) continuously with minimal tissue damage and disturbance to the normal physiological state. Using a distributed, dynamic model of the measurement system, we simulated the effects of this flow measurement method under isothermal and adiabatic boundary conditions. Numerical results show that the adiabatic boundary condition can provide maximal sensitivity to perfusion changes at physiological perfusion levels. The constant power and constant temperature operating modes are compared in terms of output relation, sensitivity, and frequency response through analytical and numerical solutions. While the steady-state relations between thermistor measurements and perfusion for the two modes do not differ significantly, the constant temperature mode has better frequency response. Analytical results show that the relative sensitivity is the same for the two modes and is approximately proportional to the radius of thermistor. If there is an unperfused layer surrounding the thermistor, the sensitivity will decrease as the thickness of the layer increases. Simulations predict that the thermal measurement has a low-pass frequency response and the cutoff frequency is inversely proportional to the probe surface area. The results provide a theoretical foundation to the optimal design of thermistor probe for continuous CBF measurement from tissue surface.
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Affiliation(s)
- D T Wei
- Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH 44106
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Artru AA, Michenfelder JD. Canine cerebral metabolism and blood flow during hypoxemia and normoxic recovery from hypoxemia. J Cereb Blood Flow Metab 1981; 1:277-83. [PMID: 7328143 DOI: 10.1038/jcbfm.1981.32] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
There are conflicting reports regarding the effects of hypoxemia on the cerebral metabolic rate for oxygen (CMRO2). Accordingly, we examined the changes in CMRO2 during normoxia, progressive hypoxia (PaO2 of 37, 27, and 23 mm Hg), and normoxic recovery from hypoxia. Measurements were made in dogs anesthetized with nitrous oxide (60-70%) and halothane (less than 0.1%) in oxygen. Arterial-cerebral venous blood oxygen content differences and cerebral blood flow (CBF) were measured simultaneously, the latter by a technique (collection of sagittal sinus outflow) previously validated for conditions of near-maximal CBF. The duration of each of the three hypoxic exposures was approximately 10 min. CMRO2 was significantly decreased (14%) only when the arterial blood oxygen tension was reduced to 23 mm Hg. CBF increased progressively to a maximum of 153% of control. Posthypoxemic brain biopsy values for cerebral metabolites obtained 40 min after normoxemia had been restored were normal. These results, in conjunction with an unchanged CMRO2 at 40 min normoxic recovery, suggest that no gross irreversible brain cell damage occurred. We conclude that with progressive hypoxemia, CMRO2 remains stable until oxygen demand exceeds oxygen delivery, resulting thereafter in a progressive reduction in CMRO2.
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Aver L. A method for continuous monitoring of pial vessel diameter changes and its value for dynamic studies of the regulation for cerebral circulation. A preliminary report. Pflugers Arch 1978; 373:195-8. [PMID: 565046 DOI: 10.1007/bf00584860] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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Scheinberg P, Meyer JS, Reivich M, Sundt TM, Waltz AG. XIII. Cerebral circulation and metabolism in stroke. Cerebral circulation and metabolism in stroke study group. Stroke 1976; 7:212-34. [PMID: 772892 DOI: 10.1161/01.str.7.2.212] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
An understanding of the cerebral circulation is so fundamental to comprehension of the pathogenesis of stroke that cerebral blood flow and metabolism merit review in this series of reports. The authors recognize that the research described here is very technical in nature and may appear to have little practical application to clinical medicine. Nevertheless, these matters are basic to the development of precise methods for the measurement of regional cerebral blood flow in man which could be used to monitor the therapy of stroke with greater success than is possible at present.
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