Noninvasive assessment of bowel blood perfusion using intraoperative laser speckle flowgraphy.

PURPOSE: Laser speckle flowgraphy (LSFG) is a noninvasive method for quantitative evaluation of blood flow using the mean blur rate (MBR) as the blood flow index. We investigated whether LSFG can intraoperatively detect the demarcation line after vessel dissection and reduce the incidence of anastomotic leakage (AL). METHODS: This study included 36 patients who underwent left-sided colorectal surgery. First, we compared the demarcation line (determined by LSFG) with the transection line (TL) at which the marginal vessels were divided. We then measured the MBR on both sides of the TL to determine where the MBR changed significantly. We investigated the presence or absence of significant differences between the MBR on the proximal side and that on the distal side of the TL. Finally, we retrospectively compared the patient characteristics and AL rates in the LSFG group (n = 36) and control group (n = 87). RESULTS: In total, 58.3% (21/36) of the demarcation lines determined by LSFG matched the TL. The median distance between the demarcation line determined by LSFG and the TL was 0.0 mm (0.0-12.1 mm). The MBR sharply decreased at the TL in 80.6% (29/36) of cases. The median MBR was significantly lower on the distal than proximal side. The AL rate was not significantly lower in the LSFG group than in the control group. CONCLUSION: LSFG accurately detected the demarcation line during surgery. However, LSFG did not reduce the incidence of AL.

Validation of speed-resolved laser Doppler perfusion in a multimodal optical system using a blood-flow phantom.

The PeriFlux 6000 EPOS system combines diffuse reflectance spectroscopy (DRS) and laser Doppler flowmetry (LDF) for the assessment of oxygen saturation (expressed in percentage), red blood cell (RBC) tissue fraction (expressed as volume fraction, %RBC), and perfusion (%RBC × mm / s) in the microcirculation. It also allows the possibility of separating the perfusion into three speed regions (0 to 1, 1 to 10, and >10 mm / s). We evaluate the speed-resolved perfusion components, i.e., the relative amount of perfusion within each speed region, using a blood-flow phantom. Human blood was pumped through microtubes with an inner diameter of 0.15 mm. Measured DRS and LDF spectra were compared to Monte Carlo-simulated spectra in an optimization routine, giving the best-fit parameters describing the measured spectra. The root-mean-square error for each of the three speed components (0 to 1, 1 to 10, and >10 mm / s, respectively) when describing the blood-flow speed in the microtubes was 2.9%, 8.1%, and 7.7%. The presented results show that the system can accurately discriminate blood perfusion originating from different blood-flow speeds, which may enable improved measurement of healthy and dysfunctional microcirculatory flow.

Low-cost compact diffuse speckle contrast flowmeter using small laser diode and bare charge-coupled-device.

We report a low-cost compact diffuse speckle contrast flowmeter (DSCF) consisting of a small laser diode and a bare charge-coupled-device (CCD) chip, which can be used for contact measurements of blood flow variations in relatively deep tissues (up to ∼ 8 mm). Measurements of large flow variations by the contact DSCF probe are compared to a noncontact CCD-based diffuse speckle contrast spectroscopy and a standard contact diffuse correlation spectroscopy in tissue phantoms and a human forearm. Bland­Altman analysis shows no significant bias with good limits of agreement among these measurements: 96.5%±2.2% (94.4% to 100.0%) in phantom experiments and 92.8% in the forearm test. The relatively lower limit of agreement observed in the in vivo measurements (92.8%) is likely due to heterogeneous reactive responses of blood flow in different regions/volumes of the forearm tissues measured by different probes. The low-cost compact DSCF device holds great potential to be broadly used for continuous and longitudinal monitoring of blood flow alterations in ischemic/hypoxic tissues, which are usually associated with various vascular diseases.

A new, fast LDI for assessment of burns: a multi-centre clinical evaluation.

INTRODUCTION: Laser Doppler imaging (LDI) provides early accurate determination of wound healing potential. LDI can scan large areas of up to 2500 cm2 within 2 min. This duration may require additional sedation in a mobile, uncooperative child. In five burn centres a faster Laser Doppler Line Scanner (LDLS) was assessed. This new imager scans 300 cm2 in 4s with potential benefit for patients and operators. The aim of this study was to assess the accuracy and convenience of the LDLS and to compare this with an established LDI imager. METHODS: Outpatients and admitted patients were included. LDI and LDLS images were obtained between 2 and 5 days post burn (PB). Photographs and records of wound and healing were obtained on day of scan and at 14 and 21 days PB. This provided data on three categories of burn wounds: healing within 14 days, 14-21 days and not healed within 21 days. RESULTS: The analysis included 596 burn areas from 204 burns patients. An accuracy of 94.2% was found with use of the LDLS compared with 94.4% for the original LDI imager. CONCLUSIONS: The high accuracy of the new line-scan imager was comparable to that of the traditional LDI. Its size and mobility enabled easier ward and outpatient use. The higher scan speed was particularly beneficial for scans in paediatric patients.

FluxEXPLORER: a new high-speed laser Doppler imaging system for the assessment of burn injuries.

BACKGROUND: Deep burn assessment made by clinical evaluation has an accuracy varying between 60% and 80% and will determine if a burn injury will need tangential excision and skin grafting or if it will be able to heal spontaneously. Laser Doppler Imaging (LDI) techniques allow an improved burn depth assessment but their use is limited by the time-consuming image acquisition which may take up to 6 min per image. METHODS: To evaluate the effectiveness and reliability of a newly developed full-field LDI technology, 15 consecutive patients presenting with intermediate depth burns were assessed both clinically and by FluxExplorer LDI technology. Comparison between the two methods of assessment was carried out. RESULTS: Image acquisition was done within 6 s. FluxEXPLORER LDI technology achieved a significantly improved accuracy of burn depth assessment compared to the clinical judgement performed by board certified plastic and reconstructive surgeons (P < 0.05, 93% of correctly assessed burns injuries vs. 80% for clinical assessment). CONCLUSION: Technological improvements of LDI technology leading to a decreased image acquisition time and reliable burn depth assessment allow the routine use of such devices in the acute setting of burn care without interfering with the patient's treatment. Rapid and reliable LDI technology may assist clinicians in burn depth assessment and may limit the morbidity of burn patients through a minimization of the area of surgical debridement. Future technological improvements allowing the miniaturization of the device will further ease its clinical application.

Evaluation of a new device for the intraoperative assessment of coronary artery bypasses grafting.

PURPOSE: The aim of this study was to evaluate a new flow analyze device that can intraoperatively measure compliance and resistance of coronary artery bypass grafting (CABG) by the parameter identification method. METHODS: Subjects were 95 patients who underwent CABG. Angiography soon after surgery confirmed patency in 90 grafts and graft failure in 5 grafts. Variables of aortic pressure and the graft flow were entered into this new device that includes a mathematical coronary circulation model to extrapolate other information the data; thus, we can estimate intraoperative flow rate, resistance, and compliance. Flow rate, resistance, and compliance were compared between patent and failed graft groups and among three different type grafts. RESULTS: There were no differences in flow rate, resistance, and compliance among the three grafts types. Between the patent and failed graft groups, there were statistically significant differences in flow rate and resistance, and compliance tended to be lower for the failed graft group. CONCLUSIONS: By measuring graft resistance and compliance, this new device is useful for evaluating graft performance during CABG.

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.

Critical review of burn depth assessment techniques: part II. Review of laser doppler technology.

The judgment of which wounds are expected to heal within 21 days is one of the most difficult and important tasks of the burn surgeon. The quoted accuracy of 64 to 76% by senior burn surgeons underscores the importance of an adjunct technology to help make this determination. A plethora of techniques have been developed in the last 70 years. Laser Doppler imaging (LDI) is one of the most recent and widely studied of these techniques. The technology provides an estimate of perfusion through the burn wound, the assumption being that a lower perfusion correlates with a deeper wound and, therefore, a longer time to heal. Although some reports suggest accuracy between 96 and 100% and that it does this 2 days ahead of clinical judgment, others have questioned its applicability to clinical practice. This article, the second of a two-part series, has two objectives: 1) a review of the Doppler principle and how the LDI uses it to estimate perfusion; and 2) a critical assessment of the burn literature on the LDI. Part I provides a historical perspective of the different technologies used through the last 70 years to assist in the determination of burn depth. Laser Doppler has brought technology closer to provide a reliable adjuvant to the clinical prediction of healing, yet, caution is warranted. A clear understanding of the limitations of LDI is needed to put the current research in perspective to find the right clinical application for LDI.

Evaluation of a new high power, wide separation laser Doppler probe: potential measurement of deeper tissue blood flow.

OBJECTIVE: To compare the output from a novel high power, wide separation laser Doppler flow probe (DP1-V2-HP, 4 mm, with IRLD20) with that of a standard flow probe (DP1-V2, 0.5 mm, with DRT4) (Moor UK) and to explore its potential for use in the noninvasive measurement of blood flow in deeper tissues in humans. METHODS: Monte Carlo modeling was used to predict depths of light scattering in skin with each probe, geometry. Experimentally, forearm blood flow was measured at rest and during local warming of the skin surface and post occlusion reactive hyperaemia (PORH). Laser Doppler blood flux (LDF) and the power spectral density of its component frequency intervals, were compared. RESULTS: Monte Carlo modeling indicated that while the majority of wide probe LD signal derives from deeper tissue, a significant portion is from superficial (dermal) tissue (and vice versa for standard probe). Perturbation of local blood flow differentially increased LDF and spectral power as measured by the two probes, with the standard skin probe showing a significantly greater response to local skin warming (p<0.01). CONCLUSIONS: These differences support our hypothesis that the wide probe is recording predominantly blood flux within the vasculature of sub-dermal tissue. This is in agreement with Monte Carlo simulation.

Assessment of bone vascularity in the anterior mandible using laser Doppler flowmetry.

OBJECTIVES: In irradiated bone, a method assessing vascularity of intended implant recipient bone would be of clinical significance in preventing early implant loss and in reducing the risk of osteoradionecrosis due to surgical oral implant insertion. At present, assessing bone vascularity clinically, using laser Doppler flowmetry (LDF), seems to be realistic. The hypotheses of this study were that bone vascularity in the human anterior mandible can be assessed during implant insertion by LDF and that the recorded LDF values are providing standard data for bone vascularity in the human anterior mandible. MATERIAL AND METHODS: Twenty-three randomly selected non-irradiated edentulous patients scheduled for treatment with oral implants in the anterior mandible were assigned, 12 men and 11 women. The patients' history of edentulousness and resorption of the residual alveolar ridges were registered. In pilot osteotomy sites of planned implant insertion, the bone vascularity was registered, using LDF and expressed in perfusion units (PU). The statistical distribution and characteristics of the LDF values were explored, separately for men and women. RESULTS: A total of 41 pilot osteotomy sites were recorded with a mean LDF value of 25.80 PU. No obvious gender difference was found and LDF values did not show a relationship with patient's age or history of edentulousness. CONCLUSION: The hypotheses that bone vascularity in the human anterior mandible can be assessed during implant insertion by LDF and that the recorded LDF values are providing standard data for bone vascularity in the human anterior mandible, were confirmed.

Renal viability evaluated by the multiprobe assembly: a unique tool for the assessment of renal ischemic injury.

BACKGROUND: One of the major causes of transplanted organs' dysfunction is ischemia-reperfusion injury, where mitochondrial dysfunction is the primary contributor to cell damage. Mitochondrial NADH fluorescence reliably describes intracellular oxygen deficiency and mitochondrial function. Therefore, its monitoring at the tissue level, together with other physiological parameters, can serve to evaluate tissue vitality. METHODS: The multiprobe assembly (MPA) enabled the assessment of renal blood flow (RBF) using laser Doppler flowmetry, mitochondrial NADH redox state using the fluorometric technique, and ionic homeostasis using specific mini-electrodes (K(+) and H(+)). The MPA was utilized in two rat groups in which ischemia was induced for a period of 25-30 min (group 1) or for 60 min (group 2), and RBF and NADH were also monitored in a group of rats that underwent a complete kidney ischemia 24 h before the monitoring - a well-known model of acute renal failure. RESULTS: During ischemia, the RBF was completely abolished, NADH and extracellular potassium levels increased, and extracellular pH decreased. Immediately after the reperfusion, full recovery was observed; however, in the rats undergoing 60-min ischemia followed by 24-hour reperfusion, the tissue hemodynamic and mitochondrial functions were significantly impaired. CONCLUSION: This study demonstrates the advantage of using the MPA for real-time evaluation of kidney physiological state, which may serve as a practical instrument for the evaluation of graft viability during transplantation procedures.

Assessment of oxygenation and perfusion in the tongue and oral mucosa by visible spectrophotometry and laser Doppler flowmetry in healthy subjects.

UNLABELLED: Use of Visible Light Spectrophotometry (VLS) and Laser Doppler Flowmetry (LDF) is currently being studied by the authors to assess the viability of tissue margins in colon resection and to assess mucosal oxygenation in the colon. Thus, as a preliminary study it was necessary to evaluate whether there is any systematic inter-probe variability of the measurements by VLS and LDF. The oral mucosa was used as a model. METHODS: SO2 with VLS (Whitland Research RM200) and blood flow with LDF (Moor Instruments DRT4) were measured at 10 sites each on the tongue and oral mucosa of 10 healthy volunteers at 0, 6 and 24 hours using 3 different probes for VLS and 2 probes for LDF. RESULTS: The results showed that the SO2 measurements by VLS using the different probes on the tongue and mucosa were significantly correlated (P < 0.05). SO2 values at 6 hours were significantly higher than at 0 and 24 hours (P < 0.05) in all but one case. SO2 measurements were not correlated with LDF. LDF measurements by the 2 probes were correlated significantly (P < 0.05) but the standard deviations were very large. CONCLUSIONS: SO2 measurements on the oral mucosa are reproducible. Due to the large variations in LDF, VLS is likely to be the more clinically useful tool for identifying mucosal ischaemia.

A device for noninvasive assessment of vascular impairment risk in the lower extremity.

The repeatability and resolution of the clinical gold standard of vascular assessment, the ankle-brachial index (ABI), was compared to that of a new device that dynamically assesses tissue perfusion during external loading utilizing laser Doppler flowmetry. Eight subjects of varying levels of vascular impairment were tested in successive weeks using two different sites on the subject's posterior calf. These new measures included the perfusion decrease as well as the unloading delay during cyclic loading. Some new dynamic tissue perfusion measures demonstrated comparable levels of reproducibility with the ABI (e.g., 10%-20%). Only the unloading delay showed potentially enhanced resolution over ABI measures. The perfusion decrease showed little resolution, and the remaining parameters exhibited too great variability (25%-90%). The unloading delay associated with the reperfusion response during cyclic loading displayed the greatest combination of reproducibility and differentiation between subject groups of varying levels of vascular impairment. The preliminary results of this pilot study were also used to estimate sample sizes necessary to detect possible significant (P<0.05) differences between subject groups for all measured perfusion parameters. From these calculations, at least 30 subjects are needed for future study in each of the five subject groups.

Assessment of vascularity in irradiated and nonirradiated maxillary and mandibular minipig alveolar bone using laser doppler flowmetry.

PURPOSE: The purpose of this animal study was to confirm that laser Doppler flowmetry (LDF) is a reproducible method for the assessment of maxillary and mandibular alveolar bone vascularity and that there is less vascularity in irradiated mandibular and maxillary bone compared to nonirradiated bone. MATERIALS AND METHODS: All maxillary and mandibular premolars and molars of 6 Göttingen minipigs were extracted. After a 3-month healing period, 3 minipigs received irradiation at a total dose of 24 Gy. Three months after irradiation, 5 holes were drilled in the residual alveolar ridge of each edentulous site in each minipig. Local microvascular blood flow around all 120 holes was recorded by LDF prior to implant placement. In 1 irradiated and 1 nonirradiated minipig, an additional hole was drilled in a right maxillary site to enable repeated LDF recordings. RESULTS: The alveolar bone appeared less vascularized in irradiated than in nonirradiated minipigs. The effect of radiation appeared more pronounced in the mandible than in the maxilla. LDF was demonstrated to be a reproducible method for assessing alveolar bone vascularity. However, recordings varied by edentulous site as well as by minipig. CONCLUSION: The authors' hypotheses regarding LDF and vascularity were supported. Further research validating the use of LDF in human beings, especially in those who have undergone radiation therapy for head and neck cancer, is necessary.

Assessment of abnormal blood flow and efficacy of treatment in patients with systemic sclerosis using a newly developed microwireless laser Doppler flowmeter and arm-raising test.

Background Patients with systemic sclerosis (SSc) frequently suffer from recalcitrant digital ulceration because of impaired cutaneous blood flow (CBF). A simple and accurate CBF measurement would be helpful to evaluate the disease status and efficacy of treatment in such patients. Objectives To examine the feasibility of a newly developed, micromachined integrated laser blood flowmeter (MILBF) for evaluation of abnormal CBF responses in patients with SSc. Methods CBF of finger pulp was measured in eight patients with SSc and in six healthy controls using MILBF. CBF in the steady state and the responses to the arm-raising test and cold provocation were assessed. The therapeutic efficacy of a single and an intensive prostaglandin E(1) (PGE(1)) infusion treatment was also evaluated in some of the SSc patients. Results The patients with SSc showed significantly lower steady-state CBF than controls. The rate of blood flow with cold provocation and the velocity of blood flow recovery after cold provocation (VR-CP) tended to be lower in patients with SSc. Augmentation of amplitude of the digital pulse wave by arm raising (AA-AR) was observed in controls, but not in patients with SSc. We also found that VR-CP and AA-AR may be good markers for evaluating the efficacy of vasodilatory treatment. It should be noted that the examined patients did not complain of any pain and/or distress during the arm-raising test, as opposed to during cold provocation. Conclusions CBF assessment using MILBF and an arm-raising test is accurate, noninvasive and well tolerated and thus the combination may be a better alternative method to evaluate abnormal CBF and efficacy of treatment in patients with SSc.

Assessment of variation in bulbar conjunctival redness, temperature, and blood flow.

PURPOSE: To assess the diurnal variation in bulbar conjunctival redness, conjunctival temperature, and conjunctival blood flow. METHODS: Bulbar redness was quantified by CIE u' chromaticity using a SpectraScan PR650 spectrophotometer. Conjunctival temperature was measured using a Tasco-Thi 500 infrared thermometer. Measurements of conjunctival blood flow were obtained using a modified Heidelberg Retinal Flowmeter (HRF). Measurements on 10 subjects were made on a periodic basis over the day and on waking. RESULTS: For each factor measured a cyclical pattern was observed, with highest values on waking, a reduction in values towards mid-day, and then a gradual increase over the remainder of the day. There was a significant effect of time for redness, temperature, and conjunctival blood flow (p < 0.001 for all three variables), with no significant difference in the cyclical pattern between eyes being observed (p = NS). CONCLUSIONS: Diurnal bulbar redness, temperature, and conjunctival blood flow variation may be objectively quantified and all three are lowest during the middle of the day and maximal at the start of the day. This information should be considered when undertaking studies in which redness, temperature, and ocular surface blood flow are important outcome variables and time of day is a potential confounding factor.

Noninvasive assessment of cutaneous vascular function in vivo using capillaroscopy, plethysmography and laser-Doppler instruments: its strengths and weaknesses.

Given that functional abnormalities of the microcirculation are one of the primary abnormalities in cardiovascular disease pathogenesis, various noninvasive clinical tools have been developed recently to assess the microvascular function, particularly at the skin. The common techniques used to assess cutaneous microvascular function in vivo include capillaroscopy, venous occlusion plethysmography, and laser-Doppler instruments (laser-Doppler fluximetry and laser-Doppler imaging). These noninvasive techniques can be used as an early measure of functional abnormalities within the microvascular tree, predominantly in population at high risk for cardiovascular events. This review discusses some underlying application principle of these techniques, including its clinical significance, method reproducibility and limitations.

Preliminary study on the assessment of peripheral vascular response to cold provocation in workers exposed to hand-arm vibration using laser Doppler perfusion imager.

Measurements of changes in finger skin blood flow with laser Doppler perfusion imaging (LDPI) in response to cold provocation test (10 degrees C, 10 min) were performed in 12 men suffering from vibration induced white finger (VWF) and 13 exposed controls. The mean perfusion values in both groups reduced markedly as a result of immersion of the hand in cold water. In the controls, however, the mean value increased gradually until the end of the cold provocation, while that in the VWF subjects remained at the lowest level. After removal of the hand from the cold water, the skin blood perfusion in the controls recovered rapidly and nearly reached the baseline value. In the VWF subjects, it had a slight increase immediately following the cold immersion but no tendency to rise as the time span increased. Analysis of covariance controlling for possible confounders revealed that the VWF subjects had significantly lower perfusion values compared to the controls in the last several minutes of the cold provocation and the following recovery. These findings suggest that the LDPI technique enables visualizing and quantifying the peripheral vascular effects of cold water immersion on the finger skin blood perfusion and thus has the potential of providing more detailed and a&curate information that may help detect the peripheral circulatory impairment in the fingers of vibration-exposed workers.