Characteristics of laser Doppler perfusion imaging in vitro and in vivo

Protocol and recruitment results from a 13-week randomized controlled trial comparing the effects of different doses of nitrate-rich beetroot juice on cognition, cerebral blood flow and peripheral vascular function in overweight and obese older people

BACKGROUND

Nitrate-rich food can increase NO production and may induce positive effects on brain function. This study examined the feasibility of a randomized clinical trial (RCT) testing the effects of prolonged consumption of incremental doses of dietary nitrate (NO3 -) in overweight and obese older participants. Secondary aims tested dose-dependent changes in cognitive, vascular and pulmonary functions and cerebral blood flow (CBF).

METHODS

This was a single blind, four-arm parallel RCT conducted in 60 overweight and obese older participants. Eligible participants were randomized to:1) high NO3 - (140 ml of beetroot juice (BJ) per day, ~800 mg of NO3 -/day), 2) moderate NO3 - (70 ml of BJ per day, ~400 mg of NO3 -/day), 3) low NO3 - (70 ml on alternate days, ~400 mg of NO3 -) or 4) NO3 - depleted (70 ml on alternate days, ~0.001 mg of NO3). Measurements of cognitive, vascular and pulmonary functions and CBF were conducted at baseline and 13-weeks NO3 - intake was assessed by six 24-h recalls, and by measuring NO3 - intake biomarkers. Feasibility was assessed by obtaining qualitative feedback and evaluating trial recruitment, retention, compliance with study visits and measurement protocols.

RESULTS

Participant recruitment started in July 2018 and ended in April 2019. Of all the recruitment strategies that were used, advertisement of the study via Facebook generated the highest response rate. Sixty-two participants consented and were enrolled. Overall, characteristics of included participants matched our recruitment criteria.

CONCLUSION

The findings from this study provide evidence of the acceptability and feasibility of an intervention investigating the effects of incremental doses of high-nitrate BJ over a prolonged period.

TRIAL REGISTRATION

The intervention study was registered with clinical trial ISRCTN registry (ISRCTN14746723) on 27 December 2018.

Distribution pattern of common drugs of abuse, ethyl glucuronide, and benzodiazepines in hair across the scalp

While hair analysis is important and accepted in forensic applications, fundamental knowledge gaps still exist, exacerbated by a lack of knowledge of the incorporation mechanisms of substances into hair. The influence of the hair sampling location on the head on ethyl glucuronide (EtG) and cocaine concentrations was investigated by measuring the complete scalp hair of 14 (2 EtG, 4 cocaine, 8 both EtG and cocaine) study participants in a grid pattern for EtG, drugs of abuse, and benzodiazepines. Head skin perfusion and sweating rates were investigated to rationalize the concentration differences. For EtG, ratios between maximum and minimum concentrations on the scalp ranged from 2.5 to 7.1 (mean 4.4). For cocaine, the ratios ranged from 2.8 to 105 (mean 17.6). EtG concentrations were often highest at the vertex, but the distribution was strongly participant dependent. Cocaine and its metabolites showed the lowest concentrations at the vertex and the highest on the periphery, especially at the forehead. These differences led to hair from some head parts being clearly above conventional cut-offs and others clearly below. In addition to EtG and cocaine, the distributions of 24 other drugs of abuse and benzodiazepines/z-substances and metabolites are described. No clear pattern was observed for the head skin perfusion. Sweating rate measurements revealed higher sweating rates on the periphery of the haircut. Therefore, sweat could be a main incorporation route for cocaine. Concentration differences can lead to different interpretations depending on the sampling site. Therefore, the results are highly relevant for routine forensic hair analysis.

Validation of phototesting for estimation of individual skin ultraviolet sensitivity based on a lengthwise attenuating ultraviolet B field

Conventional skin UV-sensitivity phototesting is based on semi-quantitative assessment of minimal erythema dose (MED). This study demonstrates a method for quantitative MED determination, using a lengthwise attenuating UVB-field combined with tissue viability imaging (TiVi). The study aim was to investigate the agreement between MED acquired by traditional phototest and by the new method. Forty-seven voluntary subjects underwent phototesting with a traditional phototest and with the new technique. Test reading, carried out after 24 h, showed moderate agreement between the methods when assessed with TiVi (Kappa value=0.46) and visually (Kappa value=0.48). For the new method, no systematic differences were seen between outcomes assessed with TiVi or visually (95% CI for the mean difference=-1.6-2.0). In conclusion, the results give promising support for the concept of achieving a more precise MED estimation by combining continuous attenuating UV fields with new available bioengineering technology.

Laser Doppler imaging as a tool in the burn wound treatment protocol

INTRODUCTION

The main treatment of burns is early excision of injured tissues.

AIM

TO COMPARE TWO DIFFERENT METHODS OF EXAMINATION OF BURNED PATIENTS: clinical burn depth examination (CDE) and laser Doppler imaging (LDI).

MATERIAL AND METHODS

A prospective randomized study of 57 burn patients treated in 2009-2011 was carried out. The burned patients were randomized into a CDE group and an LDI group. The CDE and LDI scan were performed 72 h after injury, with the second and third CDE and LDI scan on the 7(th) and 14(th) day after the burn. Age, sex, length of inpatient stay, cost of burn treatment, burn depth, cause and localization of the burns were analyzed between the two groups.

RESULTS

Fifty-seven patients were treated during 2 years. Thirty-two patients were in the CDE group and 25 patients were in the LDI group. Most of the patients were male (45 male vs. 12 female, p < 0.001). The age was similar between the males and the females (female: 46.4 ±16.9 years vs. male: 46.3 ±12.5 years; p = 0.11). The mean length of stay in hospital was significantly higher in the CDE group (47 ±34.4 day vs. 25 ±10.8 day; p = 0.005). The mean cost of treatment of burned patients was significantly higher in the CDE group.

CONCLUSIONS

The length of stay and cost of treatment of burn patients depends upon early diagnosis of the deep burns and well-timed surgical treatment of burn wounds.

EVALUATION OF ACUPUNCTURE WEIGHT LOSS PROGRAMME USING LASER DOPPLER PERFUSION IMAGING

Recent development of non-invasive and remote sensing modalities such as the Laser Doppler Perfusion Imager (LDPI) technology for probing the skin blood perfusion and its spatial variability over a region of interest, allows for detailed analysis of alterations in skin blood perfusion, with virtually no disturbance of the microcirculation under study. In this study, we have investigated perfusion flux pattern changes obtained from the abdominal area of 30 Chinese male patients (mean age of 26, presented only 2 typical cases) undergoing an acupuncture slimming course. The objective was to study the alterations in skin blood flux by detailed analysis of the Doppler images taken before, during which and after the insertion of needles. We explained the correlation of alterations of skin blood flux with the flow of Qi and the losses of body weight and body fat content. The purpose was to quantify a relationship between changes in perfusion flux pattern and the efficacy of weight loss through acupuncture. In conclusion, this study affirmed that skin blood perfusion flux values in the abdominal area were the highest, whilst the acupuncture needles were inserted. There is also evidence that the increased flux values occurred along the meridian channels of acupuncture, thereby acknowledging the flow of Qi in them. Hence, further clinical studies in the use of LDPI to investigate acupuncture with more subjects are warranted.

ASSESSMENT OF PROXIMAL INTERPHALANGEAL JOINTS IN PATIENTS WITH OSTEOARTHRITIS VIA LASER DOPPLER PERFUSION IMAGING

The study aims to determine whether the LDPI technique can provide an objective indication of synovial hyperaemia associated with inflamed finger joints. In addition, it hopes to obtain more information about the influence of pain and stiffness on the cutaneous blood flow and assess whether skin perfusion can be used as an index to evaluate these clinical parameters of Osteoarthritis.

Except for the deformed joint, the red laser source (λ = 632.8 nm, visible red) failed to detect any hyperaemic areas associated with joint inflammation in patients with Osteoarthritis (OA). Measurements taken over the PIP joints of both groups have shown a good repeatability for all between-day measurements. However, the variation in between-day perfusion of the OA group is greater compared to the normal control. For majority of the subjects, perfusion in the adjacent skin tends to be lower and fluctuate less than that in their PIP joints. The study also indicates some correlation between the blood perfusion with pain and stiffness of the finger joints.

Overall, the present finding suggests that a longer wavelength near-infrared laser have considerable potential for this form of imaging and that LDI can offer a convenient means of rapidly assessing an inflamed joint non-invasively. Further clinical studies in these areas are warranted.

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.

Hyperoxia decreases cutaneous blood flow in high-perfusion areas

The mechanism by which hyperoxia decreases blood flow is still not understood. Hyperoxemia-induced vasoconstriction is known to occur in many organs, including brain and retina, skeletal muscle, and myocardium. Whether this also occurs in skin is unknown. This study was conducted in healthy volunteers exposed intermittently to 100% oxygen (F(I)O(2) 1.0). Perfusion of forearm skin was measured by laser Doppler imaging (LDI). In series 1, it was measured in 7 subjects before, during, and after 15 min of oxygen breathing. In series 2, flow was measured, also during air and O(2) breathing, after perfusion was raised by (a) sympathetic blockade (induced by a topically applied local anesthetic) (n=9) and by (b) current-induced vasodilation (n=8). In normal unperturbed skin, there was no significant change with hyperoxia. When basal perfusion was raised by topical anesthesia or by current, there was also no change in mean perfusion overall with hyperoxia. However, areas with the highest perfusion (upper decile) showed a significant perfusion decrement with hyperoxia (-30% and -20%, respectively; p<0.001). Vasoconstriction with hyperoxia has been demonstrated in human skin. The fact that it is observed only when flow is increased above basal levels and then only in high-flow vessels suggests that cutaneous blood flow control is primarily regulated by variables other than oxygen.

Laser Doppler imaging in the investigation of lower limb wounds

Good blood supply is a primary determinant for the healing of acute and chronic wounds alike. Chronic wounds commonly occur in the lower extremity in man. Scientists are forever looking for objective techniques with which tissue perfusion may be measured with accuracy. Laser Doppler imaging is a very useful technique for measuring microvascular perfusion in wounds because it involves no contact and produces a color image representing flow distribution over an area of tissue. In this article, the authors discuss its application to the assessment of lower limb wounds, and they review published studies in which it has been used to investigate a range of wound types. This review examines the study of healing mechanisms, treatment effects, risk prediction, healing potential, and underlying pathology. It also considers areas in which laser Doppler imaging is still to be exploited fully.

Impaired microvascular function related to poor metabolic control in young patients with diabetes

The purpose of the present study was to identify whether young patients with type 1 diabetes using modern multiple insulin injection therapy (MIT) have signs of microvascular dysfunction and to elucidate possible correlations with various disease parameters. Skin blood flow on the dorsum of the foot was measured with laser Doppler perfusion imaging in 37 patients (age 10-21 years, disease duration 6.0-16 years) and 10 healthy controls. Measurements were performed at rest, after change in posture (the leg was lowered below heart level) and during postocclusive hyperaemia. Following a change in posture blood flow increased instead of decreased in a majority of the study subjects. Patients with acute HbA1c >7.5% (n = 22) had an increase in skin blood flow at rest and a significantly reduced blood flow when the leg was lowered below heart level as compared with patients with HbA1c <7.5% (0.26 V versus 0.17 V, P<0.01 and 0.12 V versus 0.23 V, P<0.05, respectively) and healthy controls. Following occlusion of the macrocirculation for 3 min a small non-significant decrease in the hyperaemic response was seen in the patients. The postocclusive hyperaemic response and the venoarteriolar reflex were not correlated to duration of disease, long-term metabolic control or electrophysiological signs of peripheral nerve dysfunction. It is concluded that signs of microvascular dysfunction related to poor metabolic control are present in young patients with MIT treatment and rather well-controlled diabetes. Low resting blood flow levels are suggested to contribute to the absence of postural vasoconstrictor response.

A new technique to map vulva microcirculation using laser Doppler perfusion imager

The location of the vulva has had limited technologic progress in the assessment of the skin microcirculation and its application to clinical practice. Our group previously demonstrated increased perfusion in vulvar cancer compared to adjacent uninvolved skin with the laser Doppler flowmetry (LDF). The LDF is severely limited by its low spatial resolution ( approximately 1 mm(2)) and pressure involved in positioning of the probe, which may affect value of the underlying tissue perfusion. Topographic perfusion mapping of the whole vulvar skin using LDF is also time consuming and is not clinically practical. We describe for the first time the application of the novel laser Doppler perfusion imager (LDPI) to map vulvar skin blood flow and give example in two cases with well-defined vulvar pathology-psoriasis and lichen sclerosus with invasive neoplasia-and discuss the potential of LDPI to study vulvar skin blood flow.

Laser Doppler, speckle and related techniques for blood perfusion mapping and imaging

Laser Doppler velocimetry uses the frequency shift produced by the Doppler effect to measure velocity. It can be used to monitor blood flow or other tissue movement in the body. Laser speckle is a random interference effect that gives a grainy appearance to objects illuminated by laser light. If the object consists of individual moving scatterers (such as blood cells), the speckle pattern fluctuates. These fluctuations provide information about the velocity distribution of the scatterers. It can be shown that the speckle and Doppler approaches are different ways of looking at the same phenomenon. Both these techniques measure at a single point. If a map of the velocity distribution is required, some form of scanning must be introduced. This has been done for both time-varying speckle and laser Doppler. However, with the speckle technique it is also possible to devise a full-field technique that gives an instantaneous map of velocities in real time. This review article presents the theory and practice of these techniques using a tutorial approach and compares the relative merits of the scanning and full-field approaches to velocity map imaging. The article concludes with a review of reported applications of these techniques to blood perfusion mapping and imaging.

Measurement of depth of burns by laser Doppler perfusion imaging

Laser Doppler perfusion imaging (LDPI), is a further development in laser Doppler flowmetry (LDF). Its advantage is that it enables assessment of microvascular blood flow in a predefined skin area rather than, as for LDF, in one place. In many ways this method seems to be more promising than LDF in the assessment of burn wounds. However, several methodological issues that are inherent in the LDPI technique, and are relevant for the assessment of burn depth, must be clarified. These include the effect of scanning distance, curvature of the tissue, thickness of topical wound dressings, and pathophysiological effects of skin colour, blisters, and wound fluids. Furthermore, we soon realised that to examine the perfusion image generated by LDPI adequately the process of analysis was appreciably improved by the simultaneous use of digital photography. In the present investigation we used both in vitro and in vivo models and also examined burned patients, and found that the listed factors all significantly affected the LDPI output signal. However, if these factors are known to the examiner, most of them can be adjusted for. If the technique is further improved by minimizing such effects and by reducing the practical difficulties of applying it to a burned patient in the burns unit, the technique may find uses in everyday clinical decision-making.