Hyperspectral imaging for monitoring of perfusion failure upon microvascular anastomosis in the rat hind limb

BACKGROUND/PURPOSE

Objective, reliable and easy monitoring of microvascular tissue perfusion is a goal that was achieved for many years with limited success. Therefore, a new non-invasive hyperspectral camera system (TIVITA™) was tested for this purpose in an in vivo animal model.

METHODS

Evaluation of tissue oxygenation during ischemia and upon reperfusion was performed in left hind limb in a rat model (n=20). Ischemia was induced by clamping and dissection of the superficial femoral artery. Reperfusion of the limb was achieved by microsurgical anastomosis of the dissected artery. Oxygenation parameters of the hind limb were assessed via TIVITA™ before and immediately after clamping and dissection of the artery, 3 and 30min after reperfusion as well as on postoperative days 1 and 2. Thereby, the non-operated hind limb served as control. As clinical parameters, the refill of the anastomosis as well as the progress of the affected leg were assessed.

RESULTS

In 12 from 20 cases, TIVITA™ recorded a sufficient reperfusion with oxygenation parameters comparable to baseline or control condition. However, in 8 from 20 cases oxygenation was found impaired after reperfusion causing a re-assessment of the microvascular anastomosis. Thereby, technical problems like stenosis or local thrombosis were found in all cases and were surgically treated leading to an increased tissue oxygenation.

CONCLUSIONS

The TIVITA™ camera system is a valid non-invasive tool to assess tissue perfusion after microvascular anastomosis. As it safely shows problems in oxygenation, it allows the clinician a determined revision of the site in time in order to prevent prolonged ischemia.

Assessment of skin blood flow following spinal manual therapy: a systematic review

Skin blood flow (SBF) indexes have been used to describe physiological mechanisms associated with spinal manual therapy (SMT). The aims of the current review were to assess methods for data collection, assess how investigators interpreted SBF changes, and formulate recommendations to advance manual medicine research. A database search was performed in PubMed, Cochrane Library, the Physiotherapy Evidence Database, and the Cumulative Index to Nursing and Allied Health Literature through April 2014. Articles were included if at least 1 outcome measure was changes in 1 SBF index following SMT. The database search yielded 344 records. Two independent authors applied the inclusion criteria. Twenty studies met the inclusion criteria. Selected studies used heterogeneous methods to assess short-term post-SMT changes in SBF, usually vasoconstriction, which was interpreted as a general sympathoexcitatory effect through central mechanisms. However, this conclusion might be challenged by the current understanding of skin sympathetic nervous activity over local endothelial mechanisms that are specifically controlling SBF. Evaluation of SBF measurements in peripheral tissues following SMT may document physiological responses that are beyond peripheral sympathetic function. Based on the current use of SBF indexes in clinical and physiological research, 14 recommendations for advancing manual medicine research using laser Doppler flowmetry are presented.

The interrelation of endothelial function and microvascular reactivity in different vascular beds, and risk assessment in hypertension: results from the Doxazosin-ramipril study

There are several non-invasive methods to study endothelial function, but their interrelation and association to cardiovascular risk have not been well evaluated. We studied macrovascular and microvascular endothelial function simultaneously in different vascular beds in relation to cardiovascular mortality risk (Systematic Coronary Risk Evaluation, SCORE) and hypertension induced cardiac organ damage, and their interrelationship. The study investigated 71 hypertensive patients by forearm post-ischemic flow-mediated vasodilation, pulse wave analysis (applanation tonometry) and beta 2-adrenoceptor agonist stimulation for changes in reflection index, skin microvascular reactivity by laser Doppler fluxmetry with iontophoresis and heat-induced hyperaemia, and coronary microvascular function by subendocardial viability ratio (derived from pulse wave analysis). Flow mediated vasodilation related inversely to SCORE (r =  0.34, P = 0.011). Adding microalbuminuria and pulse wave velocity strengthened the associations. Pulse wave reflection changes did not relate to SCORE. Skin microvascular reactivity related inversely to SCORE (peak flux change to sodium nitroprusside r =  0.29, P = 0.033, and to heating r =  0.31, P = 0.018). Subendocardial viability ratio did not relate to SCORE. Endothelial function indices showed no consistent relation to cardiac target organ damage. The agreement between the different methods for evaluating indices of macrovascular and microvascular endothelial function was weak. In conclusion, indices of macrovascular and microvascular endothelial function relate to cardiovascular mortality risk. Their use may improve cardiovascular risk prediction in hypertension. However, methods representing different vascular beds show little interrelationship and are not interchangeable, which may depend on different pathogenetic mechanisms representing different aspects of future cardiovascular risk.

Trial registry: NCT02901977

Intravital microscopy and image analysis of Rhodnius prolixus (Hemiptera: Reduviidae) hematophagy: the challenge of blood intake from mouse skin

Hematophagous insects transmit many of the most dangerous parasitic diseases. The transmission usually occurs during hematophagy or just after as this is when the vector and the host are in contact. The contact time is determined by the feeding performance of the insect in each host. In triatomines, feeding performance interferes with both their life cycle and the vectorial competence to transmit the hemoflagellate Trypanosoma cruzi. Triatomine bugs are vessel feeders, obtaining their blood meals directly from the vessels (venules or arterioles) of their vertebrate hosts. The host blood intake rate is not constant during the feeding, and the sucking frequency of triatomines tends to be higher and to contain fewer interruptions in pigeons than in mice. To identify the difficulties encountered by triatomine bugs in obtaining blood meals from mouse skin, we used intravital microscopy techniques associated with electromyograms of the cibarial pump. To monitor the vibration of the cannulated vessels and the blood flow through the head of the insect during the engorgement phase, we introduced a novel method for image analysis. The mean number of vessels used during a Rhodnius prolixus blood meal was 3.4±1.2, and the insects fed more in venules (63%) than in arterioles (37%). An important increase in vascular permeability was observed throughout the feeding. Platelet aggregation, rolling and leukocyte adherence were analyzed on the venular endothelium, showing remarkable increases for some time following the R. prolixus feeding. The reduction in sucking frequency that was observed during insect feeding was likely due to the increased cibarial pump filling time. The monitoring of the vessel wall pulsation also permitted the registration of regurgitation-like movements during blood pumping, with these movements being recorded mostly during the second half of the feeding. The evaluation of blood flow through the head of the insect suggested that the regurgitation-like movements were not true regurgitations and were caused by abrupt difficulties in the function of the cibarial pump. The role of the platelet plugs and the changes in blood viscosity at the R. prolixus feeding site are discussed. The method introduced in the present study to analyze the images brings new insights into the interaction between hematophagous vectors and their hosts, reinforcing the importance of insect saliva throughout the feeding process.

Reproducibility of four frequently used local heating protocols to assess cutaneous microvascular function

BACKGROUND

Skin microvascular responses to local heating are frequently used to assess microvascular function. Several local heating protocols have been developed, all varying slightly in execution. The aim of this study was to determine the inter-day reproducibility of the four most commonly used local heating protocols in healthy young subjects.

METHODS

Fifteen, healthy males (28±5yrs, BMI 25±2kg/m²) attended two experimental trials 2-7days apart. During each trial, baseline and maximal thermally stimulated forearm skin responses were examined simultaneously at four sites on the dominant forearm using laser Doppler flowmetry (LDF). The following heating protocols were adopted: 1. Rapid 39°C (0.5°C/5s), 2. Rapid 42°C (0.5°C/5s) 3. Gradual 42°C (0.5°C/2min 30s) and 4. Slow 42°C (0.5°C/5min). The coefficient of variation (CV) was calculated for absolute flux, cutaneous vascular conductance (CVC; flux/mean arterial pressure, MAP) and CVC expressed as a percentage of maximal CVC at 44°C (%CVC_max) at three different time points; baseline (33°C), plateau (39/42°C) and maximal (44°C).

RESULTS

Reproducibility of baseline flux, CVC and %CVC_max was 17-29% across all protocols. During the plateau, Rapid, Gradual and Slow 42°C demonstrated a reproducibility of 13-18% for flux and CVC and 5-11% for %CVC_max. However, Rapid 39°C demonstrated a lower reproducibility for flux, CVC and %CVC_max (all 21%). Reproducibility at 44°C was 12-15% for flux and CVC across all protocols.

CONCLUSION

This is the first study examining inter-day reproducibility across four local heating protocols. The good-to-moderate reproducibility of the Rapid, Gradual and Slow 42°C protocols support their (simultaneous) use to assess microvascular function. Using Rapid 39°C may require a greater number of subjects to detect differences within subjects.

Regional differences of vasodilatation and vasomotion response to local heating in human cutaneous microcirculation

BACKGROUND

The aim of this study was to evaluate the vasodilatation and vasomotion response to local heating in the cutaneous microcirculation of the ankle, dorsum of foot and forearm. Recently, it has been suggested that this response differs between the forearm and the leg.

PROBANDS AND METHODS

Twenty-nine young healthy adults were recruited. They underwent measurement by laser Doppler flowmetry (LDF) in three sites of the body (ankle, dorsum of foot, forearm). Percentage change of the median flow of the skin before and after provocation and normalised perfusion flow to maximal dilation (cutaneous vascular conductance--CVC % Max) during short provocation test were monitored. Spectral analysis of laser Doppler flowmetry signals was performed using the fast Fourier transform algorithm.

RESULTS

Significant differences were found in CVC % Max between ankle/dorsum (45.18±6.38% Max vs. 51.24±6.87% Max, respectively; p<0.05) and between ankle/forearm (45.18±6.38% Max vs. 54.49±5.37% Max, respectively; p<0.05). Percentage change of flux after provocation has revealed significant differences between ankle/dorsum (394.1±204.5% vs. 577.4±273.5%, respectively; p<0.05) and ankle/forearm (394.1±204.5% vs. 637.1±324.7%, respectively; p<0.05). Total spectral activity of vasomotion has differed between ankle/dorsum and ankle/forearm: 69.59 [49.58-96.04] vs. 93.01 [73.15-121.8] (p<0.05) and 69.59 [49.58-96.04] vs. 107.5 [80.55-155.8] (p<0.05), respectively.

CONCLUSIONS

Cutaneous microcirculation exhibits regional differences. Significant variability of function between ankle and dorsum of foot suggests that leg microcirculation is not uniform.

Assessment of hand superficial oxygenation during ischemia/reperfusion in healthy subjects versus systemic sclerosis patients by 2D near infrared spectroscopic imaging

BACKGROUND AND OBJECTIVE

Patients affected by systemic sclerosis (SSc) develop functional and structural microcirculatory dysfunction, which progressively evolves towards systemic tissue fibrosis (sclerosis). Disease initially affects distal extremities, which become preferential sites of diagnostic scrutiny. This pilot investigation tested the hypothesis that peripheral microcirculatory dysfunction in SSc could be non-invasively assessed by 2D Near Infrared Spectroscopic (NIRS) imaging of the hand associated with Vascular Occlusion Testing (VOT). NIRS allows measurement of hemoglobin oxygen saturation (StO₂) in the blood perfusing the volume tissue under scrutiny.

METHODS

In five normal volunteers and five SSc patients we applied a multispectral oximetry imaging device (Kent camera, Kent Imaging, Calgary, Canada) to acquire StO₂ 2D maps of the whole hand palm during baseline, ischemia and reperfusion phase.

RESULTS

We found significant differences between controls and SSc patients in basal StO₂ (82.80 ± 2.51 vs 65.44 ± 7.96%, p = 0.0016), minimum StO₂ (59.35 ± 4.29 vs 40.73 ± 6.47%, p = 0.0007), final StO₂ (83.83 ± 4.09 vs 68.84 ± 11.41%, p = 0.02) and time to maximum StO₂ (40 ± 12.25 vs 62 ± 4.47 s, p = 0.005).

CONCLUSIONS

This is, to our knowledge, the first application of 2D NIRS imaging of the whole hand to the investigation of microvascular dysfunction in systemic sclerosis. The image processing presented here considered the StO₂ in the entire hand allowing a comprehensive view of the spatial heterogeneity of microvascular dysfunction.

Impaired Microcirculation in Children After Kidney Transplantation: Everolimus Versus Mycophenolate Based Immunosuppression Regimen

BACKGROUND/AIMS

Whether the immunosuppressive regimen is associated with micro- and macro-vascular status in pediatric kidney transplant recipients (KTx) is unknown.

METHODS

We performed a cross-sectional, case-control study in 44 pediatric KTx patients on either everolimus (EVR) plus calcineurin inhibitor or standard treatment, i.e. mycophenolate mofetil plus calcineurin inhibitor. Measurement of carotid intima-media thickness (cIMT) via ultrasound, central pulse wave velocity (PWV) by a cuff-based oscillometric technique, and skin microvascular blood flow during local heating via laser-Doppler-fluximetry (LDF) served as marker of subclinical vascular disease. Serum concentrations of angiopoietin-1 and -2, fibroblast-growth factor 23 (FGF23) and soluble klotho were measured.

RESULTS

EVR-treated patients exhibited a similar degree of hypertension, increased cIMT, elevated pro-inflammatory angiopoietin-2, and diminished endothelial survival factor angiopoietin-1 compared to healthy children but presented with a twofold more reduced skin micro-vascular function compared to standard treatment (each p< 0.001). By contrast, PWV and soluble klotho levels were normal in both groups.

CONCLUSION

Endothelial dysfunction seems more frequent in KTx patients on EVR-based immunosuppressive regimen compared to standard immunosuppression.

Endothelial dysfunction during long-term follow-up in children with STEC hemolytic-uremic syndrome

BACKGROUND

Shiga-toxin-producing Escherichia coli (STEC)-associated hemolytic-uremic syndrome (HUS) is a major cause of acute kidney injury (AKI), especially in children. Its long-term outcome with respect to endothelial damage remains largely elusive.

METHODS

This was a cross-sectional study in 26 children who had suffered from STEC-HUS in the past and achieved a complete recovery of renal function (eGFR >90 ml/min/1.73 m²). Skin microcirculation after local heating was assessed by laser Doppler fluximetry, carotid-femoral pulse wave velocity (PWV), carotid intima media thickness (cIMT), 24-h ambulatory blood pressure, and angiopoietin (Ang) 1 and 2 serum levels after a median follow-up period of 6.1 years. The results were compared to those of healthy controls.

RESULTS

All patients were normotensive, mean eGFR was 102 (range 91-154) ml/min/1.73 m², and 13 of the 26 patients showed albuminuria. Endothelial dysfunction was present in 13 patients, and the mean serum Ang2/Ang1 ratio was increased compared to healthy children (each p < 0.05). In contrast, mean values for PWV and cIMT in the patients did not differ from those of the controls. Endothelial dysfunction was significantly associated with younger age at STEC-HUS manifestation, time after HUS, and presence of albuminuria.

CONCLUSION

The results of this study highlight the need for long-term follow-up of STEC-HUS patients even after complete recovery of eGFR and lack of hypertension with respect to microvascular damage.

Characterization of microvessels in the human forehead dermis using intravascular dual perfusion and immunofluorescence staining

Skin microcirculation provides essential insights in clinical practice. However, the specific characteristics and distribution patterns of dermal microarterioles and microvenules remain insufficiently explored. This study aimed to analyze their structural differences and distribution in the human forehead skin using an innovative intravascular dual perfusion technique combined with immunofluorescence staining to distinguish microvessel types within the dermis. Using two post-mortem cadaver specimens, lead oxide-gelatin perfusion was applied to label microarterioles, and latex was used for microvenules. Tissue sections underwent hematoxylin and eosin and immunofluorescence staining, with cluster of differentiation 31 (CD31) serving as a general vascular marker and monocarboxylate transporter 1 (MCT1) as a venule-specific marker. The analysis revealed significant structural differences between dermal layers: vessels in the deep dermis had larger diameters and thicker walls than those in the superficial layer, while microvessel density was higher in the superficial dermis. These findings demonstrate distinct patterns and significant differences in microvessel distribution between the superficial and deep dermal layers, reflecting their layer-specific functional demands. Furthermore, MCT1 was identified as a specific marker for microvenules, and a novel method combining CD31 and MCT1 immunofluorescent staining was introduced to differentiate dermal microarterioles from microvenules. These results offer valuable implications for surgical planning, skin grafting, and diagnostics related to microcirculation.

Endothelial dysfunction in subfertile women with polycystic ovary syndrome

RESEARCH QUESTION

Is there an association between post-occlusive reactive hyperaemia (PORH) and ovarian stimulation in women with normoandrogenaemic polycystic ovary syndrome (PCOS)?

DESIGN

Women eligible for IVF at an academic fertility centre were invited to join this prospective study. Microvascular endothelial function was measured as PORH by laser Doppler flowmetry (LDF) before and after ovarian stimulation. Metabolic characteristics, hormone profiles and biochemical markers were analysed.

RESULTS

Thirty-four normoandrogenaemic women with PCOS and 36 normoandrogenaemic women without PCOS were included. The PCOS group displayed higher C-reactive protein levels and insulin resistance (P = 0.048 and P = 0.025, respectively). No significant difference was found in microcirculatory function between the groups at baseline. After ovarian stimulation, PORH was enhanced in the control group (slope 7.1 ± 3.3 versus 9.7 ± 4.5; P = 0.007; peak flow 30.7 ± 16.3 versus 43.5 ± 17.3, P = 0.008; however, the PCOS group experienced a blunting response to supraphysiological hormone status (slope 8.2 ± 5.1 versus 7.2 ± 4.3, P = 0.212; peak flow, 38.8 ± 19.4 versus 37.0 ± 21.8, P = 0.895).

CONCLUSIONS

Impaired microcirculatory function could be found using a non-invasive LDF technique in normoandrogenaemic women with PCOS undergoing IVF, indicating early changes in vascular endothelial dysfunction. Future observational studies should clarify whether PORH measurement might help predict IVF prognosis or obstetric complications.