Measurement Of Capillary Blood Flow Research Articles

Nailfold capillaroscopy: tips and challenges.

Although nailfold capillaroscopy (NFC) appears to have a bright future in clinical practice, the lack of familiarity with the technique and how to interpret its outcomes is major barriers which have made nailfold capillaroscopy an underutilized method in standard clinical practice. Traditional methods for assessment and measurement of capillary patterns, density, and blood flow are falling behind and face some challenges. In fact, there have been calls for improvement, hence the recent publication of the standardization of NFC by the EULAR Study Group on Microcirculation in Rheumatic Diseases. Nailfold capillaroscopy has the advantage of being a non-invasive technique that provides a window into the digital microcirculation. This paved the way for a rapidly growing interest in using capillaroscopy parameters as outcome measures in research. In standard clinical practice, whilst its main application is in the identification of an underlying systemic sclerosis spectrum disorder in patients presenting with Raynaud's phenomenon, its use has expanded to include other clinical features possibly suggestive of an underlying connective tissue disease. This article presents the challenges, provides tips, and highlights the exciting potential of nailfold capillaroscopy in standard practice.

Imaging the Retinal Vasculature.

Advances in retinal imaging are enabling researchers and clinicians to make precise noninvasive measurements of the retinal vasculature in vivo. This includes measurements of capillary blood flow, the regulation of blood flow, and the delivery of oxygen, as well as mapping of perfused blood vessels. These advances promise to revolutionize our understanding of vascular regulation, as well as the management of retinal vascular diseases. This review provides an overview of imaging and optical measurements of the function and structure of the ocular vasculature. We include general characteristics of vascular systems with an emphasis on the eye and its unique status. The functions of vascular systems are discussed, along with physical principles governing flow and its regulation. Vascular measurement techniques based on reflectance and absorption are briefly introduced, emphasizing ways of generating contrast. One of the prime ways to enhance contrast within vessels is to use techniques sensitive to the motion of cells, allowing precise measurements of perfusion and blood velocity. Finally, we provide a brief introduction to retinal vascular diseases.

Time-Efficient Perfusion Imaging Using DCE- and DSC-MRI

Abstract Dynamic contrast enhanced MRI (DCE-MRI) and dynamic susceptibility contrast MRI (DSC-MRI) are perfusion imaging techniques used mainly for clinical and preclinical measurement of vessel permeability and capillary blood flow, respectively. It is advantageous to apply both methods to exploit their complementary information about the perfusion status of the tissue. We propose a novel acquisition method that combines advantages of the current simultaneous and sequential acquisition. The proposed method consists of a DCE-MRI acquisition interrupted by DSC-MRI acquisition. A new method for processing of the DCE-MRI data is proposed which takes the interleaved acquisition into account. Analysis of both the DCE- and DSC-MRI data is reformulated so that they are approximated by the same pharmacokinetic model (constrained distributed capillary adiabatic tissue homogeneity model). This provides a straightforward evaluation of the methodology as some of the estimated DCE- and DSC-MRI perfusion parameters should be identical. Evaluation on synthetic data showed an acceptable precision and no apparent bias introduced by the interleaved character of the DCE-MRI acquisition. Intravascular perfusion parameters obtained from clinical glioma data showed a fairly high correlation of blood flow estimates from DCE- and DSC-MRI, however, an unknown scaling factor was still present mainly because of the tissue-specific r 2 * $r_2^*$ relaxivity. The results show validity of the proposed acquisition method. They also indicate that simultaneous processing of both DCE- and DSC-MRI data with joint estimation of some perfusion parameters (included in both DCE- and DSC-MRI) might be possible to increase the reliability of the DCE- and DSC-MRI methods alone.

Automated structure and flow measurement — a promising tool in nailfold capillaroscopy

ObjectivesDespite increasing interest in nailfold capillaroscopy, objective measures of capillary structure and blood flow have been little studied. We aimed to test the hypothesis that structural measurements, capillary flow, and a combined measure have the predictive power to separate patients with systemic sclerosis (SSc) from those with primary Raynaud's phenomenon (PRP) and healthy controls (HC). Methods50 patients with SSc, 12 with PRP, and 50 HC were imaged using a novel capillaroscopy system that generates high-quality nailfold images and provides fully-automated measurements of capillary structure and blood flow (capillary density, mean width, maximum width, shape score, derangement and mean flow velocity). Population statistics summarise the differences between the three groups. Areas under ROC curves (AZ) were used to measure classification accuracy when assigning individuals to SSc and HC/PRP groups. ResultsStatistically significant differences in group means were found between patients with SSc and both HC and patients with PRP, for all measurements, e.g. mean width (μm) ± SE: 15.0 ± 0.71, 12.7 ± 0.74 and 11.8 ± 0.23 for SSc, PRP and HC respectively. Combining the five structural measurements gave better classification (AZ = 0.919 ± 0.026) than the best single measurement (mean width, AZ = 0.874 ± 0.043), whilst adding flow further improved classification (AZ = 0.930 ± 0.024). ConclusionsStructural and blood flow measurements are both able to distinguish patients with SSc from those with PRP/HC. Importantly, these hold promise as clinical trial outcome measures for treatments aimed at improving finger blood flow or microvascular remodelling.

Laser speckle and hydrogen gas clearance measurements of optic nerve circulation in albino and pigmented rabbits with or without optic disc atrophy.

The purpose of this study was to evaluate the correlation between laser speckle flowgraphy measurements of mean blur rate (MBR) and hydrogen gas clearance measurements of capillary blood flow (CBF) in the optic nerve head (ONH) of albino and pigmented rabbits, with or without chronic ischemia-induced ONH atrophy. The ONH MBR and ONH CBF were measured at baseline, 30 and 60 minutes after the intravenous administration of endothelin-1 (ET-1) (10(-10) mol/kg) in six albino and six pigmented rabbit eyes. The ONH MBR and ONH CBF were also measured in nine pigmented rabbit eyes that underwent the intravitreal administration of ET-1 (20 pmol) twice per week for 4 weeks to provoke chronic ischemia-induced ONH atrophy. In the group that received intravenous ET-1, average measurements of ONH MBR and ONH CBF at all time points were correlated in both the albino (r = 0.88, P < 0.001, n = 18) and pigmented rabbits (r = 0.85, P < 0.001, n = 18), with no intrarabbit correlations (P = 0.524). The ONH MBR and ONH CBF were also correlated in the model of chronic ischemia-induced ONH atrophy (r = 0.78, P = 0.013, n = 9). Pooled ONH MBR and ONH CBF measurements in both the intravenous and intravitreal groups were also highly correlated (r = 0.87, P < 0.001, n = 45), with no significant intergroup differences in the relationship between ONH MBR and ONH CBF (P = 0.138). Regardless of the presence of fundus pigmentation or ONH atrophy, ONH MBR and ONH CBF were highly correlated, suggesting that MBR in the ONH tissue is usable for interindividual and intergroup comparisons.

Human cerebral microcirculation and oxygen saturation during propofol-induced reduction of bispectral index

Propofol reduces cerebral blood flow (CBF) secondary to cerebral metabolic depression. However, in vitro and in vivo studies demonstrate that propofol directly dilates the vascular smooth muscle. This study investigates the effects of propofol-induced changes in bispectral index (BIS) on cerebral microcirculation and oxygenation during craniotomies. In 21 craniotomy patients undergoing routine craniotomy, anaesthesia was maintained with propofol 4-10 mg kg⁻¹ h⁻¹ and remifentanil 0.1-0.4 µg kg⁻¹ min⁻¹. Propofol concentration was adjusted to achieve higher BIS (target 40) or lower BIS (target 20). Regional measurements of capillary venous blood flow (rvCBF), oxygen saturation (srvO₂), and haemoglobin amount (rvHb) at 2 mm (grey matter) and 8 mm (white matter) cerebral depth were randomly performed at higher and lower BIS by combined laser-Doppler flowmetry and spectroscopy. Calculations: approximated arteriovenous difference in oxygen content (avDO₂) and cerebral metabolic rate of oxygen (aCMRO₂). mean values (sd). Mann-Whitney test (*P<0.05). Results Human cerebral microcirculation and oxygen saturation were assessed at propofol dosages 5.1 (2.3) mg kg⁻¹ h⁻¹ [BIS 40 (9)] and 7.8 (2.1) mg kg⁻¹ h⁻¹ [BIS 21 (7)]. Propofol-induced reduction in BIS resulted in increased srvO₂ (P=0.018), and decreased avDO₂ (P=0.025) and aCMRO(2) (P=0.022), in 2 mm cerebral depth, while rvCBF and rvHb remained unchanged. In 8 mm cerebral depth, srvO₂, rvCBF, rvHb, and also calculated parameters avDO₂ and aCMRO₂ remained unaltered. Findings suggest alteration of the CBF/CMRO₂ ratio by propofol in cortical brain regions; therefore, it might be possible that propofol affects coupling of flow and metabolism in the cerebral microcirculation.

A novel, microscope based, non-invasive laser Doppler flowmeter for choroidal blood flow assessment

Impaired ocular blood flow is involved in the pathogenesis of numerous ocular diseases like glaucoma or AMD. The purpose of the present study was to introduce and validate a novel, microscope based, non-invasive Laser Doppler Flowmeter (NI-LDF) for measurement of blood flow in the choroid. The custom made NI-LDF was compared with a commercial fiber optic based laser Doppler flowmeter (Perimed PF4000). Linearity and stability of the NI-LDF were assessed in a silastic tubing model (i.d. 0.3 mm) at different flow rates (range 0.4–3 ml/h). In a rabbit model continuous choroidal blood flow measurements were performed with both instruments simultaneously. During blood flow measurements ocular perfusion pressure was changed by manipulations of intraocular pressure via intravitreal saline infusions. The NI-LDF measurement correlated linearly to intraluminal flow rates in the perfused tubing model ( r = 0.99, p < 0.05) and remained stable during a 1 h measurement at a constant flow rate. Rabbit choroidal blood flow measured by the PF4000 and the NI-LDF linearly correlated with each other over the entire measurement range ( r = 0.99, y = x∗1.01–12.35 P.U., p < 0.001). In conclusion, the NI-LDF provides valid, semi quantitative measurements of capillary blood flow in comparison to an established LDF instrument and is suitable for measurements at the posterior pole of the eye.

Pulmonary Capillary Blood Flow and Cardiac Output Measurement by Partial Carbon Dioxide Rebreathing in Patients with Acute Respiratory Distress Syndrome Receiving Lung Protective Ventilation

Pulmonary Capillary Blood Flow and Cardiac Output Measurement by Partial Carbon Dioxide Rebreathing in Patients with Acute Respiratory Distress Syndrome Receiving Lung Protective Ventilation

Fluid resuscitation with human albumin or hydroxyethyl starch—are there differences in the healing of experimental intestinal anastomoses?

Objectives. Restoration of the macro- and microcirculation is important for the healing of gastrointestinal anastomoses. Colloids and crystalloids are widely used for blood volume therapy. We evaluated the effects of human albumin, hydroxyethyl starch (HES) 130/0.4 and saline on the microcirculation and on wound healing in colon anastomoses in rats. Material and methods. Male Wistar rats received a colonic end-to-end anastomosis. The animals were randomized into three groups and a single 3-ml dose of either 20% human albumin, 6% HES 130/0.4 or 0.9% saline was applied intravenously. Six, 24, 48, 96 h and 2 weeks after the procedure, 10 animals per group were reanesthetized. Measurements of capillary blood flow, vessel permeability and anastomosis bursting pressure were performed. The amounts of vascular endothelial growth factor (VEGF) and IL-6 in the plasma were determined by enzyme-linked immunosorbent assays, and the mRNA levels of VEGF and collagen types I and III were measured by real-time polymerase chain reaction. Results. No significant differences were found between albumin, HES 130/0.4 and saline in capillary blood flow, vessel permeability and anastomotic bursting pressure in this rat model. Concentrations of collagen I and III mRNA were significantly elevated after 96 h in animals that had received HES 130/0.4 or albumin. RNA and protein levels of VEGF and interleukin-6 were unaffected by therapy. Conclusions. Human albumin, which is still widely used in the clinical setting, had no advantage over HES 130/0.4 and saline with regard to anastomotic healing in this animal model. Nevertheless, we prefer HES 130/0.4 because it is more effective for volume therapy than saline and has a better availability and is less expensive than human albumin.

Basic technique and anatomically imposed limitations of confocal scanning laser Doppler flowmetry at the optic nerve head level

Many studies have suggested an association between blood flow dysregulation and glaucomatous damage to the optic nerve. Confocal scanning laser Doppler flowmetry (CSLDF) is a technique that measures the capillary blood flow of the retina and optic nerve head and provides a two-dimensional map of ocular perfusion in these areas. This review discusses the anatomy of the anterior optic nerve vasculature and the capabilities and limitations of the CSLDF. Methods to minimize error and to acquire more reliable measurements of capillary blood flow are also outlined.

Pulmonary Capillary Blood Flow and Cardiac Output Measurement by Partial Carbon Dioxide Rebreathing in Patients with Acute Respiratory Distress Syndrome Receiving Lung Protective Ventilation

Partial carbon dioxide rebreathing noninvasively measures the pulmonary capillary blood flow and estimates the cardiac output with the use of a predicted shunt value. It has been reported that the accuracy of the method is decreased in patients with high pulmonary shunt. The aim of this study was to investigate the agreement between partial rebreathing and thermodilution for the determination of pulmonary capillary blood flow and cardiac output in the setting of acute respiratory distress syndrome. Twenty consecutive patients with the acute respiratory distress syndrome were enrolled. Ventilator settings include low tidal volume (6 ml x kg(-1)) and positive end-expiratory pressure + 2 cm H2O higher than the lower inflection point if present or 10 cm H2O if not. Seven pairs of cardiac output and pulmonary capillary blood flows were recorded every 20 min over a 2-h period. The authors determined bias, SD, limit of agreement (95% confidence interval) and percentage error. Bias and agreement for cardiac output measurement were 0.8 +/- 1.2 l x min(-1) (-2.1 to 3.7 l x min(-1)), and percentage error was 36%. Bias and agreement for pulmonary capillary blood flow measurement were -0.1 +/- 0.8 l x min(-1) (-2.1 to 1.9 l x min(-1)), and percentage error was 35%. Dead space, arteriovenous oxygen content difference, mean pulmonary arterial pressure, and baseline cardiac output were independently associated with differences between methods. In patients with the acute respiratory distress syndrome, partial rebreathing cannot yet replace thermodilution for measuring pulmonary capillary blood flow or cardiac output. However, accuracy of the method is close to the boundary of clinical relevance.

El flujo como indicador del efecto terapéutico del ácido folínico en la isquemia-reperfusión

An intestinal reperfusion study with two aims: a) to assess the usefulness of intestinal capillary blood flow measurement by laser-Doppler for intestinal reperfusion studies; and b) to compare the effects of racemic and levo forms of folinic acid in treating the syndrome. A murine model of intestinal ischemia by completely clamping the superior mesenteric artery for 90 minutes. A comparison was made of three treatment groups: saline, folinic acid, and levo-folinic acid. The following factors were analyzed: changes in biochemical parameters (levels of creatine kinase, lactic dehydrogenase, and alkaline phosphatase at 60 minutes, and at two and seven days after restoring blood flow), capillary flow in the jejunum and ileum by laser-Doppler (during ischemia and after the first hour of reperfusion), intestinal mucosa injury, and survival curve. Laser-Doppler provided reliable data on how the different treatments affected capillary flow during intestinal reperfusion. Levo-folinic acid improved capillary flow in the ileum after 25 minutes of reperfusion, and also reduced mucosal injury in the same stretch of intestine by the seventh day post-reperfusion (p<0.05). On the other hand, it produced an initial increase in serum enzymes during reperfusion, and did not modify survival. The changes observed in intestinal capillary blood flow measurement by laser-Doppler have similarities with the effects of drugs on pathological mucosal changes. We could not prove that the levo form of folinic acid has a stronger protective effect versus racemic folinic acid in intestinal ischemia-reperfusion syndrome.

Evaluation of Laser Doppler Flowmetry for Measurement of Capillary Blood Flow in the Stomach Wall of Dogs During Gastric Dilatation‐Volvulus

To validate laser doppler flowmetry (LDF) for measurement of blood flow in the stomach wall of dogs with gastric dilatation-volvulus (GDV). Six purpose-bred dogs and 24 dogs with naturally occurring GDV. Experimental and clinical. Capillary blood flow in the body of the stomach and pyloric antrum was measured with LDF (tissue perfusion unit (TPU) before and after induction of portal hypertension (PH) and after PH plus gastric ischemia (GI; PH + GI) and compared with flow measured by colored microsphere technique. Capillary flow was measured by LDF in the stomach wall of dogs with GDV. PH and PH+GI induced a significant reduction in blood flow in the body of the stomach (P = .019). A significant positive correlation was present between percent changes in capillary blood flow measured by LDF and colored microspheres after induction of PH + GI in the body of the stomach (r = 0.94, P = .014) and in the pyloric antrum (r = 0.95, P = .049). Capillary blood flow measured in the body of the stomach of 6 dogs that required partial gastrectomy (5.00+/-3.30 TPU) was significantly lower than in dogs that did not (28.00+/-14.40 TPU, P = .013). LDF can detect variations in blood flow in the stomach wall of dogs. LDF may have application for evaluation of stomach wall viability during surgery in dogs with GDV.

Comparison of two systems for measurement of pulmonary capillary blood flow by partial CO2 rebreathing

de Abreu, Gama M.; Winkler, T.; Pahlitzsch, T.; Weismann, D.; Koch, T. Author Information

Non-invasive measurement of intrapulmonary shunt during inert gas rebreathing

We tested the agreement between non-invasive measurement of intrapulmonary shunt, using oxygen uptake and pulmonary capillary blood flow measurement obtained by nitrous oxide rebreathing, with that measured using mixed venous blood sampling. Nine patients were recruited pre- and post-cardiac surgery resulting in 20 sets of measurements overall. Mean shunt fraction was 12.5%, and bias between methods (±95% confidence limits) was −0.7% (±0.8%). The standard deviation of the difference was 1.7% with limits of agreement between the two methods of +2.6% and −3.9%. Correlation coefficient r was 0.90. Agreement with the invasive standard was less accurate and precise where cardiac output was measured by bolus thermodilution (mean bias +1.6%, standard deviation of the difference 2.2%, limits of agreement between the two methods of +5.8% and −2.8%, r = 0.86). Good agreement was demonstrated between the non-invasive method and the invasive reference standard.

A noninvasive partial carbon dioxide rebreathing technique for measurement of pulmonary capillary blood flow is also a useful oxygenation monitor during one-lung ventilation

Study objectives To test the hypothesis that effective pulmonary capillary blood flow can be a useful indicator for estimating appropriate oxygenation and ventilation during one-lung ventilation in lung surgery. Design Prospective data analysis. Setting A 770-bed general teaching hospital. Patients 15 ASA physical status II and III patients undergoing elective lung surgery. Interventions Patients received general and thoracic epidural anesthesia and underwent lung operation with one-lung ventilation. Measurements We measured effective pulmonary capillary blood flow by a partial CO 2 rebreathing method and oxygenation parameters during two-lung ventilation before surgery, during one-lung ventilation, and during two-lung ventilation after lung surgery. Main results The effective pulmonary capillary blood flow index significantly decreased by 31.6%, which was associated with a significant decrease in arterial oxygen tension (PaO 2). The pulmonary shunt fraction increased to 46.3% during one-lung ventilation. During two-lung ventilation, after chest closure, effective pulmonary capillary blood flow index divided by heart rate (i.e., effective pulmonary blood stroke flow index) was still significantly lower than that seen during two-lung ventilation before thoracotomy. There were significant correlations between effective pulmonary capillary blood flow, pulmonary blood stroke flow index, and PaO 2. Conclusions Effective pulmonary capillary blood flow index and effective pulmonary blood stroke flow index are useful indicators for determining appropriate oxygenation therapy during one-lung ventilation.

Measurement of pulmonary capillary blood flow by partial CO2 rebreathing during one-lung ventilation

Measurement of pulmonary capillary blood flow by partial CO2 rebreathing during one-lung ventilation

Alterations of retinal capillary blood flow in preclinical retinopathy in subjects with type 2 diabetes.

To identify alterations of retinal capillary blood flow in the papillomacular area in preclinical diabetic retinopathy using the Heidelberg scanning laser Doppler flowmeter. Ten eyes from ten patients with type 2 diabetes and no lesions visible on fundus photography (level 10 of Wisconsin grading) and ten eyes from ten healthy subjects of similar age range were examined with the HRF. Intravisit reproducibility of retinal capillary blood flow measurements was assessed in normal subjects and in type 2 diabetic patients, comparing different measurement areas and different analysis procedures: (a) 10x10 pixel box with original software, (b) 10x10 pixel box with SLDF software, and (c) whole-scan analysis with SLDF software (automatic full-field perfusion image analysis). Intravisit reproducibility for the whole-scan analysis in the papillomacular area was 3.52%, 4.81% and 4.60% for volume (VOL), flow (FLW) and velocity (VEL) respectively. Using this method, mean and SD values for retinal capillary blood-flow are 13.25+/-2.87, 214.58+/-55.30 and 0.74+/-0.17, for VOL, FLW and VEL for healthy eyes, comparing with 19.85+/-6.22, 360.87+/-158.70 and 1.20+/-0.48 in eyes with preclinical diabetic retinopathy (P<0.010, P<0.019 and P<0.015 respectively). The HRF shows acceptable reproducibility when using whole-scan analysis in the papillomacular area. Retinal capillary blood VOL, FLW and VEL were particularly increased in five of the ten diabetic eyes examined, with values over the mean + 2SD of the control population, suggesting that eyes showing increased retinal capillary blood flow may indicate risk of progression.

Retinale Nervenfaser schichtdicke und peripapillärer Blutfluss bei Glaukompatienten und Gesunden

In progressive glaucoma there is increasing loss of retinal nerve fibers and therefore decreasing nerve fiber layer thickness. As measurements of capillary blood flow have been reported to depend on nerve fiber layer thickness, this could result in incorrectly high blood flow measurements in patients with advanced glaucoma. In 33 healthy controls and 59 glaucoma patients we measured retinal nerve fiber layer thickness by laser polarimetry and relative capillary blood flow by scanning laser doppler flowmetry three times on the nasal and temporal peripapillary retina. For statistical analysis a regression analysis was used. The correlation coefficients for volume, velocity, and flow with nerve fiber layer thickness at the same location were 0.02/-0.03/-0.02 in the temporal retina and -0.22/-0.07/-0.19 in the nasal retina (all correlations nonsignificant). No correlation was found between nerve fiber layer thickness and capillary blood flow. Measurement of capillary blood flow in glaucoma patients thus does not appear to be affected by decreasing nerve fiber layer thickness.

Does glutamine reduce bacterial translocation? A study in two animal models with impaired gut barrier.

Failure of intestinal barrier function and subsequent translocation of bacteria from the gut are believed to play a decisive role in the development of systemic septic complications, for example, following major trauma or major abdominal surgery. This study evaluated: (a) the effect of glutamine on colonic microcirculation and electrophysiological parameters reflecting gut barrier function, (b) the translocation of live bacteria to extraintestinal organs, and (c) disease outcome in two animal models with impaired gut barrier function. Severe acute pancreatitis or colitis was induced in rats randomized for therapy with or without glutamine (0.5 g/kg daily). After 48 h one animal group was prepared for intravital microscopy of colonic capillary blood flow and electrophysiological measurement of gut permeability; another was killed after 96 h for histological and microbiological examination. In animals with pancreatitis, glutamine (Gln) supplementation significantly improved gut permeability, i.e., Gln increased colonic transmucosal resistance from 67+/-7 to 92+/-3 Omega/cm(2) and decreased mannitol flux through the epithelium by 53%. Capillary blood flow in the colonic mucosa was improved by 25%. The prevalence of pancreatic infections was reduced from 86% in animals on standard parenteral nutrition to 33% in animals given the Gln-enriched diet (P<0.05); mortality decreased by 32%. In colitis, Gln had no significant effect on these parameters except for improving colonic capillary blood flow in colon segments not adjacent to the major injury site. Glutamine supplementation improves colonic capillary blood flow, stabilizes gut permeability, and reduces secondary pancreatic infections and mortality in severe rodent pancreatitis, but it is not helpful in colitis. This confirms previous reports that glutamine stabilizes gut barrier function only in certain diseases. Our experimental data strongly suggest that acute pancreatitis (rather than colitis) is one of the diseases with gut barrier dysfunction in which glutamine substitution may be helpful to reduce bacterial translocation and should therefore be tested in a controlled clinical trial.