cerebral blood flow monitoringcerebral blood flow monitoring

Ann Neurol. Cerebral venous blood outflow: a theoretical model based on laboratory simulation. Hum Brain Mapp. Rosenblatt K, Walker KA, Goodson C, Olson E, Maher D, Brown CHI, et al. Linear regression analysis between CBF (usually relative to its baseline values) and MAP; Monitoring of cerebrovascular reactivity (CVR) as MAP is changed. Objective: To prospectively compare the use of the cerebral blood flow monitor (c-FLOW) and transcranial Doppler (TCD) as 2 techniques for assessing brain perfusion during carotid endarterectomy. As it is highlighted in the work of Tzeng and Ainslie,3 static CA studies pose some difficulties, especially if one wants to reproduce the entire static CA curve, because of confounding effects of some covariates of MAP changes. J Clin Invest. where [HbO2] is the oxyhemoglobin concentration change measured with NIRS [units: molHbO2/mltissue] over time t, ctHb is the blood concentration of hemoglobin [units: molHbT/mlblood], SaO2 is the change in arterial saturation (units: molHbO2/molHbT), measured noninvasively with a pulse oximeter, and k is a constant (units: mltissue/gtissue) that takes into account the small-to-large vessel hematocrit ratio and the mass density of brain tissue. As previously noted, this way of extrapolating the CA static curve from a limited number of different subjects can lead to misleading results, even if the subjects are all healthy, because of individual variability and unaccounted for effects of other variables.11 It is possible that the static CA curve is more pressure passive than previously described by Lassen, or, in other words, that the CBFMAP curve in the autoregulation range is not exactly a flat plateau (as in Fig. In one study, TCD-derived and NIRS-derived metrics were superior to transient hyperemic response ratio, though an index comprised of all three was 100% sensitive in predicting the development of DCI.229 A promising advent in the ongoing care of these patients is the advance in NIRS-based metrics of CBF and CA. In other words the features of the optical signal reflect the dynamic changes in arterial blood volume. Laser speckle contrast imaging of cerebral blood flow in humans during neurosurgery: a pilot clinical study. Cerebral blood flow monitoring using a ConvGRU model based on diffuse Delayed cerebral ischemia (DCI) is one of the most feared complications of SAH. Continuous cerebral blood flow monitors are being used in critically ill neuroscience patients to assess blood flow in vulnerable regions of the brain and to evaluate the effects of treatments on these areas. 5.1. Cerebral blood flow monitoring Journal of Neuroanaesthesiology and Critical Care CC BY-NC-SA 4.0 Authors: Manikandan Sethuraman Sree Chitra Tirunal Institute for Medical Sciences and Technology. Early C, Dewey R, Peiper H, Hunt W. Dynamic pressure-flow relationships in the monkey. With the advent of transcranial Doppler ultrasound (TCD, see Sec. In fact, it is well known that CBF is affected independently by other covariates of MAP. Continuous selective intraarterial infusion of nimodipine for therapy of refractory cerebral vasospasm. Cruz J, Gennarelli T, Alves W. Continuous monitoring of cerebral hemodynamic reserve in acute brain injury: relationship to changes in brain swelling. Stroke. 16] or Kr85 [Ref. Vajkoczy P, Roth H, Horn P, Lucke T, Thome C, Hubner U, et al. Sloan M. Detection of vasospasm following subarachnoid hemorrhage. Noninvasive cerebrovascular autoregulation assessment in traumatic brain injury: validation and utility. PubMed Central In this Table, invasive techniques require surgical access, catheterization, or arterial puncture, whereas minimally invasive techniques require intravenous injection of a contrast agent. Langenbecks Arch Surg. 3.5]). Vajkoczy etal.93 determined the conductive properties, assumed to be constant, of the tissue surrounding the probe from the initial rate of propagation of the thermal field. PubMedGoogle Scholar. This is a noninvasive method to measure absolute CBF. This method uses the following components: (a)an inflatable finger cuff; (b)a photoplethysmography sensor built into the finger cuff; and (c)a pressure controller unit. Ischemic brain injury occurs in the acute stage of over 80% of severe TBIs and is common in other nontraumatic brain lesions.219 Individualizing care has led to consensus guidelines incorporating CArecent guidelines by the Neuro-Intensive Care and Emergency Medicine (NICEM) section of the European Society of Intensive Care Medicine specifically address this and suggest that CPP targets >70mmHg in brain-injured patients should be targeted only if CA is determined to be intact.220. We observe that the tissue volume VT is intended to include the blood that perfuses it, and that the blood volume fraction, or cerebral blood volume (CBV), is assumed to stay constant. 2003;74(8):10539. The two filters are notated with H where HRC-LP(c) is an RC low-pass filter describing the capillary compartment, and HG-LP(v) is a Gaussian low pass filter describing the venous compartment. CrossRef 2014;1(1), Mangraviti A, Volpin F, Cha J, Cunningham SI, Raje K, Brooke MJ, et al. J Clin Invest. 2006;37(8):203943. J Basic Clin Physiol Pharmacol. Cerebral Blood Flow Monitoring in. Tonometry of the radial artery is carried out by placing a handheld tonometer (strain gauge pressure sensor) over the radial artery and applying a mild pressure in order to induce a partial occlusion of the artery. For data analysis of static CA, essentially three methods (with some variations) have been adopted: The last method has been used mainly in those studies in which MAP (and therefore CBF) was changed only one time with respect to its baseline values. Monitoring of Cerebral Blood Flow and Metabolism in Intensive Care With rapid sequential scanning, time-concentration curves of the contrast-bolus can be constructed. 3.8.1], and diffuse correlation spectroscopy [Sec. In the oxyhemoglobin method, the inspired oxygen fraction is first lowered and then sharply increased so that the resulting sudden burst in oxyhemoglobin concentration in blood acts as a bolus.119,120 For the first few seconds of measurement with NIRS, the venous outflow of the oxygen bolus is assumed to be zero. A Review of Monitoring Methods for Cerebral Blood Oxygen Saturation Understanding the dynamic relationship between cerebral blood flow and the BOLD signal: Implications for quantitative functional MRI. It is the difference between the mean arterial pressure (MAP) and the intracranial pressure (ICP), measured in millimeters of mercury (mm Hg). Certain neurodegenerative diseases have been associated with changes in regional or global CBF. With this relation, the measurements from the autocorrelator can be fit to solutions of the correlation diffusion equation105 in order to determine values for DB, the effective Brownian diffusion coefficient of the moving scatterers, and , a parameter determined by the optical set up of the experiment. Most CT-based tools use intravenous contrast agents that some patients cannot have either due to allergy or renal dysfunction. 5.3). The CPP is defined as the difference between the mean arterial pressure (MAP), which is the weighted average of the systolic and diastolic pressure, and the intracranial pressure (ICP), which is the pressure of the cerebrospinal fluid (CSF) in the subarachnoid space. Hypertension. 2008;20(4):24955. J Neurosurg. 2009;14(3):034015. Hartmann A, Dettmers C, Schuler F, Wassmannn H, Schumacher H. Effect of stable xenon on regional CBF and the electroencephalogram in normal volunteers. Now, let us consider the blood volume that is contained within the tissue VOI, VT, and let us denote it with VB (this blood volume has units of ml, and should not be confused with CBV, which has units of mlblood/mltissue or mlblood/100gtissue and actually represents a blood volume fraction). Neurosurgery. Most of the methods assume that the input-output system MAPCBF (where MAP is the input and CBF is the output) is linear and time invariant. 2001;49(5):121422; discussion 22-3. PubMed Leiva-Salinas C, Provenzale JM, Wintermark M. Responses to the 10 most frequently asked questions about perfusion CT. AJR Am J Roentgenol. Coles JP, Fryer TD, Smielewski P, Rice K, Clark JC, Pickard JD, et al. Other techniques are also currently used to assess CA, like PET,146,147 single photon emission computed tomography (SPECT),148 magnetic resonance imaging (MRI),149,150 and DCS.104 Note that in this latter study,104 the authors have measured the changes of CBF in response to posture maneuver (by changing the angle of the bed where the subjects were lying) in healthy subjects and in patients affected by stroke (either typical or paradoxical). The Doppler effect, which results in spectral line broadening, and the intensity fluctuations are different aspects of the same phenomenon. Measurements with this method reflect a global CBF, and Kety and Schmidt found a value of 6212ml/(100gmin) in a group of 11 human subjects.34. Cerebral blood flow and autoregulation: current measurement techniques Front. J Neurosurg. Google Scholar. https://doi.org/10.1007/978-3-031-09719-5_13, DOI: https://doi.org/10.1007/978-3-031-09719-5_13. Cerebral blood flow monitoring in clinical practice - PubMed Furthermore, the variability in blood vessel diameter introduces an additional uncertainty in translating the speed of BF (in units of cm/s) into a measure of volumetric BF (in units of ml/s) in the blood vessel. Ursino M. Mechanisms of CBF regulation. Neurovascular coupling is responsible for the increase in CBF to support greater regional or global metabolic demands of the brain. In direct methods, the metrics for CA are derived from the relationships between the dynamics of MAP and CBF without any support of physiological and vascular models of cerebral hemodynamics. Correlation of transcranial Doppler sonography mean flow velocity with cerebral blood flow in patients with intracranial pathology. CBF and CA assessment is used widely in research but the transition to well accepted and standardized approaches in clinical care has been slow. When the finger cuff is inflated by a fast pneumatic servo system to achieve arterial unloading at zero transmural pressure (i.e., the arterial pressure equals the cuff pressure) the optical signal flattens out (right panel). In the model, only one (constant) value of ICP is assumed. 92 with permission of Springer. After BF is stopped, the cuff is steadily and slowly deflated and five distinct Korotkoffs sounds can be heard. Limitations of 2-dimensional blood flow measurements. 1995;82(2):604. Thompson S. Reactivity of CBF to CO2 in patients with transient cerebral ischemic attacks. J Trauma. This capability allowed for new methods of measuring a dynamic CA response. J Neurosurg. Nucl Med Commun. Ciba Found Symp. 1991;18:255. (c)The Doppler effect applies to ultrasound or optical waves that interrogate the brain tissue at a certain frequency f, and results in a frequency shift (f) and in a decay rate for the normalized intensity autocorrelation function (g2) that are directly related to the speed of blood flow (these methods are employed by Doppler ultrasound [Sec. Simal-Julian JA, Miranda-Lloret P, Evangelista-Zamora R, Sanroman-Alvarez P, de San P, Roman L, Perez-Borreda P, et al. Respir. Dewey R, Pieper H, Hunt W. Experimental cerebral hemodynamics. In neurosurgery, monitoring cerebral blood flow (CBF) is a key factor for optimal intra- and peri-operative patient management. (12)] was calculated on the basis of the relative solubility of N2O in brain tissue and in blood at equilibrium. Manual: This is an auscultatory method based on listening to the so-called Korotkoffs sounds,139,140 which are produced when an arm cuff is inflated to a pressure large enough to occlude the brachial artery and stop BF. Caplan L. Transcranial Doppler ultrasound: present status. In addition to absolute measurements of CBF0, CHS can also measure time traces of relative CBF changes, indicated with lower-case notation, cbf(t) (i.e., cbf(t)=[CBF(t)CBF0]/CBF0).131 Because perturbations of CBF and metabolic rate of oxygen cannot be distinguished in NIRS measurements,132 we assume a constant metabolic rate of oxygen. The AAMI requires that the average difference between the tested and gold standard methods does not exceed 5 mmHg, with a standard deviation of less than 8 mmHg. Instead of studying transients of MAP and CBF during a sudden change of ABP, like in the thigh cuff maneuver, other researchers have induced hemodynamic oscillations at a single161,184,185 or multiple frequencies186 and studied the phase, amplitude, and coherence relationships between MAP and CBF. Acta Neurol Scand. Iliff L, Zilkha E, BuBoulay G, Marshall J, Morsley I, Russell R, et al. A general approach to measuring CBF is based on a mass balance relationship, known as the Fick principle, applied to a physiologically inert substance x (i.e., a substance that is not metabolized in the brain) in the blood stream. Stroke. In particular, [HbD] was found to correlate with CBF in piglets,115,116 in infants undergoing surgery,117 and in critically ill patients.118 Of course, [HbD] and ScO2 can provide only relative measurements of CBF, and they rely on the assumption that other physiological factors, besides CBF, do not contribute significantly to their values. For these reasons, TCD provides only a relative index of CBF. Anesthesiology. Alterations in CBF have been of academic interest in psychiatric illnesses since the 1940s.204 Advances in technology have allowed a renewed interest in the pathophysiology and clinical biomarkers of these diseases. Google Scholar. Graham D. Ischemic brain following emergency blood pressure lowering in hypertensive patients. 2018;178:46174. Detection of systolic and diastolic ABP requires sophisticated algorithms for the analysis of the temporal trends of the pressure cuff oscillations, with different manufacturers using different algorithms.141,142, Tonometry of the radial artery provides a noninvasive assessment of the central pulse pressure waveform (pressure in the aorta). CrossRef Cerebral hypoperfusion and vascular dysfunction are thought to be related to the pathogenesis of Alzheimers disease (AD) thus implicating that the measurement of CBF might be a useful biomarker of disease incidence or progression.195 Though mostly investigational, MRI,196 SPECT,197 and NIRS198 are rapidly approaching prime time to be a useful marker of AD via a point estimate of CBF. For accurate calculation of CPP, the transducers measuring both MAP and ICP should be zeroed at the level of the foramen of Monro (external auditory meatus). Da Costa L, Fierstra J, Fisher JA, Mikulis DJ, Han JS, Tymianski M. BOLD MRI and early impairment of cerebrovascular reserve after aneurysmal subarachnoid hemorrhage. This can be a reasonable assumption for small changes of MAP and CBF, as for example during baseline data, but it should be tested for maneuvers in which MAP changes by relatively large amounts (e.g.,thigh cuff release method). Vasomotor tone, critical closing pressure, and vascular bed resistance. A typical DCS system consists of a single-wavelength, NIR, continuous-wave light source with a long coherence length (10m), multimode source fibers with diameters of 1mm, single-mode optical fibers for light detection, single-photon counting avalanche photodiodes, and an autocorrelator. Specifically, the usefulness and applications of transcranial Doppler (TCD) are discussed in detail. One simple method for differentiating different levels of CA was introduced by Aaslid etal.19 during a thigh cuff release maneuver. More recently, a dynamic NIRS model was used to derive actual CBF measurements from NIRS data.128 In Table3, we present a summary of some recent NIRS studies on CA, including the NIRS parameter used as a surrogate of CBF (if any), the method to derive a CA index, and the applications considered. New technology is making it possible to shed a light to the brain, which historically used to be a Critical closing pressure: comparison of three methods. This technique is applicable only invasively in a surgical setting. Spencer, Seattle, WA; 1991. Google Scholar. Cerebral blood flow (CBF) and cerebral autoregulation (CA) are critically important to maintain proper brain perfusion and supply the brain with the necessary oxygen and energy substrates. Regional CBF in man manipulated by direct vagal stimulation. Intraoperative laser speckle contrast imaging with retrospective motion correction for quantitative assessment of cerebral blood flow. 2019;404(4):50515. Monitoring Cerebral Blood Flow in Neurosurgical Intensive Care Steiner LA, Czosnyka M, Piechnik SK, Smielewski P, Chatfield D, Menon DK, et al. Little JR, Yamamoto YL, Feindel W, Meyer E, Hodge CP. We conclude this section with a brief comment on MAP measurements. Ultrasound Med Biol. Cerebral blood flow and the injured brain: how should we monitor and The DCS system probes the skin, skull, and CSF, in addition to the tissue region of actual interest, the brain. Continuous non-invasive optical monitoring of cerebral blood flow and Even though [HbD] and ScO2, which provide a measure of intravascular oxygenation, are not solely determined by CBF, they are nevertheless linked to CBF. Cerebral autoregulation (CA) is a developmental process that reaches maturity around term gestation and can be monitored prenatally with both Doppler ultrasound and magnetic resonance imaging (MRI) techniques. 1972;27(5):403. He L, Baker WB, Milej D, Kavuri VC, Mesquita RC, Busch DR, et al. The goal of caring for patients with severe TBI is attenuation of secondary injury that occurs minutes to days after the primary injury and is focused on maintenance of adequate cerebral perfusion and oxygenation.231 CA has been shown to be disrupted in up to one third of patients with severe TBI,232,233 making the injured brain pressure passive and highly susceptible to ongoing ischemic injury.