Microcirculatory considerations in NMR flow imaging.
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ABSTRACT:
SUBMITTER: Bassingthwaighte JB
PROVIDER: S-EPMC3362196 | biostudies-other | 1990 May
REPOSITORIES: biostudies-other
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Project description:Various noninvasive microscopic camera technologies have been used to visualize the sublingual microcirculation in patients. We describe a comprehensive approach to bedside in vivo sublingual microcirculation video image capture and analysis techniques in the human clinical setting. We present a user perspective and guide suitable for clinical researchers and developers interested in the capture and analysis of sublingual microcirculatory flow videos. We review basic differences in the cameras, optics, light sources, operation, and digital image capture. We describe common techniques for image acquisition and discuss aspects of video data management, including data transfer, metadata, and database design and utilization to facilitate the image analysis pipeline. We outline image analysis techniques and reporting including video preprocessing and image quality evaluation. Finally, we propose a framework for future directions in the field of microcirculatory flow videomicroscopy acquisition and analysis. Although automated scoring systems have not been sufficiently robust for widespread clinical or research use to date, we discuss promising innovations that are driving new development.
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Project description:Blood viscosity decreases with shear stress, a property essential for an efficient perfusion of the vascular tree. Shear thinning is intimately related to the dynamics and mutual interactions of RBCs, the major component of blood. Because of the lack of knowledge about the behavior of RBCs under physiological conditions, the link between RBC dynamics and blood rheology remains unsettled. We performed experiments and simulations in microcirculatory flow conditions of viscosity, shear rates, and volume fractions, and our study reveals rich RBC dynamics that govern shear thinning. In contrast to the current paradigm, which assumes that RBCs align steadily around the flow direction while their membranes and cytoplasm circulate, we show that RBCs successively tumble, roll, deform into rolling stomatocytes, and, finally, adopt highly deformed polylobed shapes for increasing shear stresses, even for semidilute volume fractions of the microcirculation. Our results suggest that any pathological change in plasma composition, RBC cytosol viscosity, or membrane mechanical properties will affect the onset of these morphological transitions and should play a central role in pathological blood rheology and flow behavior.
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Project description:Dynamic parameters of preload have been widely recommended to guide fluid therapy based on the principle of fluid responsiveness and with regard to cardiac output. An equally important aspect is however to also avoid volume-overload. This accounts particularly when capillary leakage is present and volume-overload will promote impairment of microcirculatory blood flow. The aim of this study was to evaluate, whether an impairment of intestinal microcirculation caused by volume-load potentially can be predicted using pulse pressure variation in an experimental model of ischemia/reperfusion injury. The study was designed as a prospective explorative large animal pilot study. The study was performed in 8 anesthetized domestic pigs (German landrace). Ischemia/reperfusion was induced during aortic surgery. 6 h after ischemia/reperfusion-injury measurements were performed during 4 consecutive volume-loading-steps, each consisting of 6 ml kg-1 bodyweight-1. Mean microcirculatory blood flow (mean Flux) of the ileum was measured using direct laser-speckle-contrast-imaging. Receiver operating characteristic analysis was performed to determine the ability of pulse pressure variation to predict a decrease in microcirculation. A reduction of ≥ 10% mean Flux was considered a relevant decrease. After ischemia-reperfusion, volume-loading-steps led to a significant increase of cardiac output as well as mean arterial pressure, while pulse pressure variation and mean Flux were significantly reduced (Pairwise comparison ischemia/reperfusion-injury vs. volume loading step no. 4): cardiac output (l min-1) 1.68 (1.02-2.35) versus 2.84 (2.15-3.53), p = 0.002, mean arterial pressure (mmHg) 29.89 (21.65-38.12) versus 52.34 (43.55-61.14), p < 0.001, pulse pressure variation (%) 24.84 (17.45-32.22) versus 9.59 (1.68-17.49), p = 0.004, mean Flux (p.u.) 414.95 (295.18-534.72) versus 327.21 (206.95-447.48), p = 0.006. Receiver operating characteristic analysis revealed an area under the curve of 0.88 (CI 95% 0.73-1.00; p value < 0.001) for pulse pressure variation for predicting a decrease of microcirculatory blood flow. The results of our study show that pulse pressure variation does have the potential to predict decreases of intestinal microcirculatory blood flow due to volume-load after ischemia/reperfusion-injury. This should encourage further translational research and might help to prevent microcirculatory impairment due to excessive fluid resuscitation and to guide fluid therapy in the future.
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Project description:BackgroundFailure to normalize lactate is associated with poor outcomes in septic shock. It has been suggested that persistently elevated lactate may result from regional ischemia due to disturbed and/or heterogenous microcirculatory blood flow.ObjectivesThe goal of this study was to determine if lactate clearance (LC) may serve as a surrogate marker for changes in microcirculatory blood flow in patients with septic shock.MethodsThis was a prospective observational study performed within a previously published clinical trial of l-carnitine for the treatment of vasopressor-dependent septic shock. Intravital video microscopy was performed at enrollment and 12 hours later, and microcirculatory flow index (MFI) was assessed. Associations between enrollment MFI, lactate, and Sequential Organ Failure Assessment (SOFA) score were determined, in addition to associations between ∆MFI, LC, and ∆SOFA. A preplanned subgroup analysis of only patients with an elevated initial lactate was performed.ResultsWe enrolled a total of 31 patients, 23 with survival and sufficient quality videos both at enrollment and at 12 hours. ∆MFI, LC, and ∆SOFA were 0.1 (interquartile range [IQR] = 0 to 0.3), 18% (IQR = -10% to 46%), and -2 (IQR = -4 to 0). Both ∆MFI and LC were associated with ∆SOFA (β = -5.3, p = 0.01; and β = -3.5, 0.047), but not with each other, even in the subgroup of patients with an initially elevated lactate.ConclusionsWe observed no association between degree of LC and change in microcirculatory blood flow in patients with septic shock. These data suggest against the hypothesis that LC may be used as a surrogate marker of microcirculatory blood flow.
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Project description:PurposeThe aim of this study is to assess the incidence of sublingual microcirculatory flow alterations, according to a predefined arbitrary cutoff value, in patients with "clinical signs of impaired organ perfusion". Secondary endpoints were the changes in microvascular flow index (MFI), "clinical signs of impaired organ perfusion", and stroke volume (SV) after fluid administration, and the differences between groups.MethodsProspective, single-center, observational study in a 22-bed mixed intensive care unit (ICU). Patients ≥18 years with invasive hemodynamic monitoring and "clinical signs of impaired organ perfusion" as the principal reason for fluid administration were included. Before and after fluid challenge, systemic hemodynamics and direct in vivo observation of the sublingual microcirculation with sidestream dark-field imaging were obtained. Microvascular flow index (MFI) <2.6 was predefined as abnormal.ResultsN = 50. At baseline, MFI <2.6 was present in 66 % of the patients. In these patients, MFI increased from 2.3 (2-2.5) at baseline to 2.5 (2.1-2.8) after fluid challenge (p = 0.003). This was accompanied by a reduction in the number of "clinical signs of impaired organ perfusion" from 2 (1-2) to 1 (0-2) (p < 0.001). However, in patients with MFI >2.6 at baseline, MFI and clinical signs changed insignificantly [2.8 (2.8-2.9) versus 2.8 (2.7-3), p = 0.45, respectively, 1 (1-2) versus 1 (1-2), p < 0.32]. These changes were not restricted to patients with a rise in SV ≥10 %.ConclusionsThese data add to the understanding that noninvasive assessment of microvascular blood flow may help to identify patients eligible for fluid therapy, and to evaluate its effect.
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Project description:Microcirculation plays a crucial role in delivering oxygen and nutrients to living tissues and in removing metabolic wastes from the human body. Monitoring the velocity of blood flow in microcirculation is essential for assessing various diseases, such as diabetes, cancer, and critical illnesses. Because of the complex morphological pattern of the capillaries, both In-vivo capillary identification and blood flow velocity measurement by conventional optical capillaroscopy are challenging. Thus, we focused on developing an In-vivo optical microscope for capillary imaging, and we propose an In-vivo full-field flow velocity measurement method based on intelligent object identification. The proposed method realizes full-field blood flow velocity measurements in microcirculation by employing a deep neural network to automatically identify and distinguish capillaries from images. In addition, a spatiotemporal diagram analysis is used for flow velocity calculation. In-vivo experiments were conducted, and the images and videos of capillaries were collected for analysis. We demonstrated that the proposed method is highly accurate in performing full-field blood flow velocity measurements in microcirculation. Further, because this method is simple and inexpensive, it can be effectively employed in clinics.
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Project description:Background: Venoarterial extracorporeal membrane oxygenation (VA-ECMO) pump flow is crucial for maintaining organ perfusion in patients with cardiogenic shock, but VA-ECMO pump flow optimization remains as a clinical challenge. This study aimed to investigate the response of sublingual microcirculation to changes in VA-ECMO pump flow. Methods: Sublingual microcirculation was measured before and after changing VA-ECMO pump flow according to the treatment plan of ECMO team within 24 h and at 24-48 h after VA-ECMO placement. In clinical events of increasing VA-ECMO pump flow, those events with increased perfused vessel density (PVD) were grouped into group A, and the others were grouped into group B. In clinical events of decreasing VA-ECMO pump flow, those events with increased PVD were grouped into group C, and the others were grouped into group D. Results: Increased PVD was observed in 60% (95% CI, 38.5-81.5%) of the events with increasing VA-ECMO pump flow. The probability of increasing PVD after increasing VA-ECMO pump flow were higher in the events with a PVD < 15 mm/mm2 at baseline than those with a PVD ≥ 15 mm/mm2 [100% (95% CI, 54.1-100%) vs. 42.9% (95% CI, 17.7-71.1%), P = 0.042]. Other microcirculatory and hemodynamic parameters at baseline did not differ significantly between group A and B or between group C and D. Conclusion: This study revealed contradictory and non-contradictory responses of sublingual microcirculation to changes in VA-ECMO pump flow. Tandem measurements of microcirculation before and after changing VA-ECMO pump flow may help to ensure a good microcirculation.
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Project description:BackgroundThe calculated plasma volume status (cPVS) was validated as a surrogate of intravascular filling. The aim of this study is to assess the cPVS in relation to sublingual perfusion and organ injury.MethodsPre- and postoperative cPVS were obtained by determining the actual and ideal plasma volume levels in surgical patients. The sublingual microcirculation was assessed using SDF imaging, and we determined the De Backer score, the Consensus Proportion of Perfused Vessels (Consensus PPV), and the Consensus PPV (small). Our primary outcome was the assessment of the distribution of cPVS and its association with intraoperative sublingual microcirculation and postoperative complications.ResultsThe median pre- and postoperative cPVS were -7.25% (IQR -14.29--1.88) and -0.4% (IQR -5.43-6.06), respectively (p < 0.001). The mean intraoperative administered fluid volume was 2.5 ± 2.5 L (1.14 L h-1). No statistically significant correlation was observed between the pre- or postoperative cPVS and sublingual microcirculation variables. Higher preoperative (OR = 1.04, p = 0.098) and postoperative cPVS (OR = 1.057, p = 0.029) were associated with postoperative organ injury and complications (sepsis (30%), anemia (24%), respiratory failure (13%), acute kidney injury (6%), hypotension (6%), stroke (3%)).ConclusionsThe calculated PVS was associated with an increased risk of organ injury and complications in this cohort.
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Project description:The clinical use of kurtosis imaging is impeded by long acquisitions and postprocessing. Recently, estimation of mean kurtosis tensor W¯ and mean diffusivity ( D¯) was made possible from 13 distinct diffusion weighted MRI acquisitions (the 1-3-9 protocol) with simple postprocessing. Here, we analyze the effects of noise and nonideal diffusion encoding, and propose a new correction strategy. We also present a 1-9-9 protocol with increased robustness to experimental imperfections and minimal additional scan time. This refinement does not affect computation time and also provides a fast estimate of fractional anisotropy (FA).1-3-9/1-9-9 data are acquired in rat and human brains, and estimates of D¯, FA, W¯ from human brains are compared with traditional estimates from an extensive diffusion kurtosis imaging data set. Simulations are used to evaluate the influence of noise and diffusion encodings deviating from the scheme, and the performance of the correction strategy. Optimal b-values are determined from simulations and data.Accuracy and precision in D¯ and W¯ are comparable to nonlinear least squares estimation, and is improved with the 1-9-9 protocol. The compensation strategy vastly improves parameter estimation in nonideal data.The framework offers a robust and compact method for estimating several diffusion metrics. The protocol is easily implemented. Magn Reson Med 76:1455-1468, 2016. © 2015 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
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Project description:Tissue capnometry may be suitable for the indirect evaluation of regional hypoperfusion. We tested the performance of a new sublingual capillary tonometer in experimental hemorrhage. Thirty-six anesthetized, ventilated mini pigs were divided into sham-operated (n = 9) and shock groups (n = 27). Hemorrhagic shock was induced by reducing mean arterial pressure (MAP) to 40 mmHg for 60 min, after which fluid resuscitation started aiming to increase MAP to 75% of the baseline value (60-180 min). Sublingual carbon-dioxide partial pressure was measured by tonometry, using a specially coiled silicone rubber tube. Mucosal red blood cell velocity (RBCV) and capillary perfusion rate (CPR) were assessed by orthogonal polarization spectral (OPS) imaging. In the 60 min shock phase a significant drop in cardiac index was accompanied by reduction in sublingual RBCV and CPR and significant increase in the sublingual mucosal-to-arterial PCO2 gap (PSLCO2 gap), which significantly improved during the 120 min resuscitation phase. There was significant correlation between PSLCO2 gap and sublingual RBCV (r = -0.65, p < 0.0001), CPR (r = -0.64, p < 0.0001), central venous oxygen saturation (r = -0.50, p < 0.0001), and central venous-to-arterial PCO2 difference (r = 0.62, p < 0.0001). This new sublingual tonometer may be an appropriate tool for the indirect evaluation of circulatory changes in shock.
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