Laser Doppler Flowmetry Probe Research Articles

Poster 225: Acetabular Labral Blood Flow Using Laser Doppler Flowmetry Before & After All- Arthroscopic Capsular Autograft Labral Reconstruction

Objectives: All-arthroscopic capsular autograft labral reconstruction has been proposed to repair complex or irreparable tears without the downside of autograft related donor-site morbidity. Cadaveric studies have suggested that the acetabular labrum receives its blood supply from radial branches of the periacetabular periosteal vascular ring that penetrate the hip capsule, with perfusion remaining intact in most hips exhibiting labral tears. Despite this, little is known about the exact course of blood flow to labral tissue or how surgical reconstruction of this region affects microvasculature during hip arthroscopy. The purpose of this study was to examine the effects of all-arthroscopic capsular autograft labral reconstruction on labral blood flow in vivo using laser doppler flowmetry (LDF) to measure microvascular perfusion. Methods: After obtaining institutional review board approval, patients ≥18 years old undergoing arthroscopic repair of the acetabular labrum by a single surgeon were consented between 2018-2022. Labral repair was performed via a previously published capsular autograft labral reconstruction technique. An LDF probe (Moor Instruments) continuously measured microvascular blood flow flux (perfusion units [PU]) within 1mm3 of surrounding labral tissue (Figure 1). LDF measurements were taken medial and lateral to the region of the tear before/after labral reconstruction and before/after labral elevation from the acetabular rim. The mean of flux measurements was expressed as a percent change from each patient’s baseline measurements. The percent change in labral perfusion was analyzed using student t-tests and one-way ANOVA using Tukey’s method for multiple comparisons. Associations between preoperative demographics and labral perfusion were analyzed using multiple regression analyses. Lending from previous literature, flux decreases ≥50% were considered clinically significant. Results: This study included 41 patients [24 males (58.5%) and 17 females (41.5%)] undergoing arthroscopic labral repair with capsular autograft reconstruction with mean [SD] age 31.3 [8.4] years, BMI 24.8 [3.3] kg/m2, lateral center edge angle (LCEA) 35.3 [4.9] degrees, Tönnis angle 5.8 [5.8] degrees, and mean arterial pressure 96.0 [10.9] mmHg. The mean [95% CI] percent change in blood flow following labral elevation was -9.24% [(-0.04) to (-18.1)]. Following labral reconstruction, the mean [95% CI] percent change in blood flow medially was -22.3% [(-11.9) to (-32.7)] and laterally -32.5% [(-23.6) to (-41.5)]. There was no significant difference between the changes in medial versus lateral perfusion (p=0.136) following repair. Unadjusted analyses stratifying for age, BMI, sex, type of impingement, Tönnis/Outerbridge class, amount of capsule used for augmentation, and suture technique revealed that none of these factors were correlated with significant differences in labral perfusion medially or laterally (p>0.05; Table 1). Multiple regression analyses controlling for demographic and intra-operative variables demonstrated that BMI, LCEA, suture technique, age, mean arterial pressure were not significantly associated with changes in medial or lateral labral perfusion (p>0.05; Table 2). Finally, all changes in flux were found to be significantly less than the 50% threshold, when comparing decreases following labral elevation (p<0.001) and labral reconstruction medially (p<0.001) and laterally (p<0.001). Conclusions: While the vascular nature of the acetabular labrum has been described in literature, preservation of labral blood flow following arthroscopic labral repair has not yet been objectively reported. This study found that techniques to preserve native hip anatomy and vascular supply may adequately maintain perfusion to labral tissue and promote healing. While laser doppler flowmetry may be affected by secondary operative factors, careful measures were taken to standardize the in vivo environment during each measurement. Additionally, blood flow measurements are only limited time assessments with no ability to speculate if observed changes are permanent or temporary. Although this study cannot be generalized to all variations of labral repair/reconstruction, these results suggest that surgeons can employ techniques that preserve microvascular tissue perfusion. The use of capsular augmentation enables preservation of the donor-tissue blood supply with local tissue transfer, suggesting that current labral repair techniques can preserve labral perfusion. [Table: see text] [Table: see text]

No impact of biological sex on nitric oxide contribution to cutaneous vascular response to 39ºC local heating

Purpose: The contribution of endothelial nitric oxide (NO) to vasodilation (%NO contribution) is a significant indicator of risk of cardiovascular disease development. Local skin heating to either 42 ºC or 39 ºC is used to determine mechanisms of vasodilation in health and disease, specifically to investigate %NO contribution. Women have lower %NO contribution in the cutaneous vasculature than men in the early follicular phase of the menstrual cycle, when the circulating vasoactive reproductive hormones are at their lowest concentration. However, this phase represents only a brief portion of the menstrual cycle. We aimed to determine the overall impact of biological sex on %NO contribution to cutaneous vasodilation utilizing a 39ºC local heating protocol, which better isolates the endothelial NO-synthase pathway. We tested women randomly during any phase of the menstrual cycle. We hypothesized that women would demonstrate greater NO-dependent cutaneous vasodilation than men in response to 39ºC local heating. Methods: Data are represented as mean(SD). An intradermal microdialysis fiber was placed in the ventral forearms of 12 men and 13 women [24.2(4.6) years]. Local heaters and laser-Doppler flowmetry probes were used to measure red blood cell flux (perfusion units, PU). Cutaneous vascular conductance (CVC) was calculated as laser-Doppler PU/mean arterial pressure. A standard 39ºC local heating protocol was conducted wherein PU was continuously collected at rest (10 minutes), then the local temperature was increased to 39ºC. After PU reached a steady plateau (~40 minutes), the NO synthase inhibitor 15 mM NG-nitro-L-arginine methyl ester (L-NAME) was perfused. Maximal vasodilation was induced by heating to 43ºC and perfusing 28 mM sodium nitroprusside and normalized to %CVCmax. %NO contribution was calculated as the absolute percentage difference between %CVCmax of 39ºC plateau and %CVCmax of L-NAME steady-state. We compared both CVC and %CVCmax between groups with two-way ANOVA and the %NO contribution with unpaired t-tests. Results: The %NO contribution was not different between sexes [men 48(23)%, women 39(17)%; P = 0.26]. There was no effect of sex on either absolute CVC [men 0.717(0.29) PU, women 0.73(0.48) PU at 39ºC phase] or %CVCmax [men 69(31)%, women 54(20)% at 39ºC phase] at any stage of the 39ºC local heating protocol (main effects P ≥ 0.08). Conclusion: These data indicate there is no impact of biological sex on the vasodilatory response of the cutaneous vasculature to 39ºC local heating in young healthy adults when women are tested at random across the menstrual cycle. Funding: National Institutes of Health Grant T-32-5T32AG049676 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Labral Reconstruction via Capsular Augmentation Maintains Perfusion to the Acetabular Labrum and Locally Transferred Autograft: An in Vivo Laser Doppler Flowmetry Analysis.

The purpose of the present study was to examine the effects of arthroscopic labral repair with capsular augmentation on blood flow in vivo with use of laser Doppler flowmetry (LDF) to measure microvascular perfusion of the labrum and autograft tissue. The present prospective case series included patients ≥18 years old who underwent arthroscopic acetabular labral repair with capsular augmentation; all procedures were performed by a single surgeon between 2018 and 2022. The LDF probe measured microvascular blood flow flux within 1 mm3 of the surrounding labral and capsular tissue of interest. Mean baseline measurements of flux were compared with readings immediately following capsular elevation and after completing labral augmentation. Blood flux changes were expressed as the percent change from the baseline measurements. The present study included 41 patients (24 men [58.5%] and 17 women [41.5%]) with a mean age (and standard deviation) of 31.3 ± 8.4 years, a mean BMI of 24.6 ± 3.4 kg/m2, a mean lateral center-edge of angle 35.3° ± 4.9°, a mean Tönnis angle of 5.8° ± 5.8°, and a mean arterial pressure of 93.7 ± 10.9 mm Hg. Following capsular elevation, the mean percent change in capsular blood flow flux was significantly different from baseline (-9.24% [95% confidence interval (CI), -18.1% to -0.04%]; p < 0.001). Following labral augmentation, the mean percent change in labral blood flow flux was significantly different from baseline both medially (-22.3% [95% CI, -32.7% to -11.9%]; p < 0.001) and laterally (-32.5% [95% CI, -41.5% to -23.6%]; p = 0.041). There was no significant difference between the changes in medial and lateral perfusion following repair (p = 0.136). Labral repair with capsular augmentation sustains a reduced blood flow to the native labrum and capsular tissue at the time of fixation. The biological importance of this reduction is unknown, but these findings may serve as a benchmark for other labral preservation techniques and support future correlations with clinical outcomes. Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Commentary: Multiple laser doppler flowmetry probes increase the reproducibility of skin blood flow measurements.

Commentary: Multiple laser doppler flowmetry probes increase the reproducibility of skin blood flow measurements.

Multiple Laser Doppler Flowmetry Probes Increase the Reproducibility of Skin Blood Flow Measurements.

Cutaneous microcirculatory perfusion is commonly measured using laser Doppler flowmetry (LDF) probes, which provide a continuous, non-invasive quantification of skin blood flow (SkBF). However, inhomogeneities in the skin’s microvasculature density contribute to a decrease in reproducibility whenever an LDF probe is removed and replaced, as is the case during pre- and post-intervention or between-day measurements. Therefore, this study aimed to determine whether increasing the total number of individual LDF probes in a localized area improves the reproducibility of the measurement. Seven laser Doppler probes were secured in a custom-made acrylic holder designed to attach to the skin’s surface easily. SkBF, local skin temperature (Tsk), and blood pressure (BP) were assessed in 11 participants (6 M, 5 F, 42 ± 15 years). SkBF and Tsk were measured from the dorsal forearm (arm trial) for 5 min. Next, the multi-laser device was moved to the lateral side of the calf (leg trial), and measurements were obtained for 5 min. Each arm and leg trial was cyclically repeated three times, and all trials were separated by intermissions lasting 10–15 min. The average SkBF and the cutaneous vascular conductance (CVC) from all possible LDF probe combinations were not statistically different across the three arm and leg trials. Two-way mixed-effects models with absolute agreement were used to compute the intraclass correlation coefficient (ICC) for CVC, and the minimum ICC increased with the addition of LDF probes. The ICC of the average CVC from seven LDF probes was 0.96 between the arm trials and 0.91 between the leg trials, which suggests that there is excellent reliability and little difference between trials following the removal and replacement of the device. Moreover, all individual ICC values from ≥3 LDF probe combinations were greater than 0.70 (i.e., good reliability). These data suggest that SkBF measurements with multiple laser Doppler probes in a custom-made holder have excellent reproducibility after replacing the probes within the same participant. Therefore, this application could provide more reproducible assessments between repeated measurements (e.g., before and after exercise or clinical procedures) where the LDF probes must be removed and replaced within the same location.

Reactive hyperaemia augments local heat-induced skin hyperaemia.

What is the central question of this study? It is valuable to be able to monitor disease- or treatment-related changes in the microcirculation. Laser Doppler flowmetry with local heating allows non-invasive monitoring of the skin microcirculation and its ability to vasodilate. Does reactive hyperaemia augment the increase in skin blood flow elicited by local heating? What is the main finding and its importance? The addition of reactive hyperaemia to local heating results in greater vasodilatation than heating alone. Thus, reactive hyperaemia can augment local heat-induced hyperaemia in the skin. The skin circulation has been proposed as a model of generalized microvascular function that could be monitored non-invasively using laser Doppler flowmetry (LDF). The response to heat hyperaemia (HH) is commonly used to monitor disease- or treatment-related changes in microvascular function. We hypothesized that reactive hyperaemia would augment the increase in skin blood flow elicited by local heating. Fourteen healthy young adults were subjected to three different conditions: reactive hyperaemia (RH; skin temperature controlled at 33°C), heat hyperaemia (HH; 42°C held for 40min) and HH+RH. Two Peltier-controlled thermomodules with LDF probes were placed on the right forearm to monitor skin blood flow continuously. A cuff was placed on the right upper arm to elicit RH by inflation to 220mmHg for 5min. This procedure was performed with the skin temperature at 33°C and again after 40min of local heating to 42°C. Beat-by-beat mean arterial pressure (MAP) obtained by a photoplethysmographic sensor on the middle finger of the left hand allowed calculation of cutaneous vascular conductance (CVC) as LDF/MAP. Both HH and RH increased LDF (P<0.0001 and P<0.0001, respectively) and CVC (P=0.0001 and P<0.0001, respectively) above baseline values. The LDF and CVC values were significantly higher during HH+RH when compared with RH or HH alone (P<0.0001). In summary, HH+RH resulted in greater vasodilatation when compared with HH or RH alone. These results indicate that RH can augment local heat-induced hyperaemia in the skin.

Применение индивидуального позиционера, спроектированного методом CAD, для световодного зонда при лазерной диагностике микроциркуляции пародонта

Objective: To perform laser Doppler flowmetry (LDF) periodontal microcirculation assessment using custom-made, computer-aided-designed probe holders manufactured by stereolithography (SLA). Methods: 66 young people aged 21-23 years old with clinically healthy periodontium were examined. The first group consisted of subjects where a custom-made probe holder was fabricated using a silicone impression mould technique. The second group consisted of subjects where a custom-made computer-aided-design probe holder made of a photopolymer by SLA was used. The basic microcirculation parameters were analysed to evaluate periodontal microcirculation by the LDF method: the PM – average perfusion value in periodontal tissues; δ – the average square deviation of the amplitude of blood flow fluctuations from the arithmetic mean value, Kv – coefficient of variation (%). Statistical processing of the results was carried out using the software package Statistica 13.0 (StatSoft Inc, USA). Results: Statistical analysis results indicated that the functional characteristics of the periodontal microcirculation using various custom-made fibre optic probe holders used in capillary blood flow monitoring had significant differences p&lt;0.05. The value of the median PM when using a silicone holder in group I was 1.6 times lower than when using a photopolymer holder in group II. The median value of the σ index when using a silicone holder in group I was 2.3 times higher than when using a photopolymer holder in group II. The median value of the Kv when using a silicone holder in group I was 2.5 times higher than when using a photopolymer holder in group II. Conclusion: A photopolymer probe holder, unlike a silicone one, provides a constant fixed distance between the periodontal tissues and the LDF probe, prevents movement or probe displacement, and makes it possible to avoid pressure on the gingival tissue, ensuring high accuracy of laser diagnostics Keywords: Functional diagnostics, LDF, microcirculation, periodontium, CAD, stereolithography.

ACUTE DIETARY NITRATE MAY IMPAIR CUTANEOUS VASCULAR CONDUCTANCE DURING LOCAL SKIN HEATING IN POSTMENOPAUSAL WOMEN

Declining estradiol production during menopause is linked to increased oxidative stress and reduced endothelial-dependent vasodilation. It is unknown whether supplementation with dietary nitrate may improve nitric oxide (NO) bioactivity and microvascular function in postmenopausal women. PURPOSE: To determine the effects of acute dietary nitrate ingestion on NO-mediated cutaneous vascular conductance (CVC) in a cohort of postmenopausal women. METHODS: In eight women (mean ± SD: age = 62 ± 4 y, BMI = 31 ± 2 kg/m2), two laser-Doppler flowmetry probes were affixed to the dorsal aspect of the forearm for measurement of red blood cell (RBC) flux during local skin heating to 39 °C and 44 °C. Assessments were made before and 3 h after ingesting 140 mL of beetroot juice containing 12.9 mmoL of inorganic nitrate. Fractional exhaled nitric oxide (FeNO) concentrations were measured at the same time points. Cutaneous vascular conductance (CVC) at 39 °C was calculated as RBC flux/ mean arterial pressure then normalized as a proportion of maximal CVC at 44°C. During the plateau phase at 39 °C, median spectral power of the endothelial NO-dependent frequency interval was analyzed using a Morlet wavelet transform. Pre-post comparisons were performed using within-sample t-tests. RESULTS: Following beetroot juice ingestion, FeNO concentrations (mean ± SD: 18 ± 8 ppb vs. 35 ± 16 ppb; p = 0.006, dz = 1.4) and spectral power of the NO-dependent frequency interval (0.01 - 0.02 Hz; p = 0.018, dz = 1.1) increased. Despite evidence for greater NO bioavailability, CVC at 39 °C was reduced (76 ± 12% vs. 50 ± 18%; p < 0.001, dz = 2.3). There was no change in maximal CVC at 44 °C (p = 0.287). CONCLUSION: A functional consequence of increased NO-bioavailability with acute dietary nitrate ingestion appears to be a diminished NO-mediated CVC response to local skin heating in our cohort of postmenopausal women with overweight and obesity. Future research should consider the effects of dietary nitrate coupled with an antioxidant supplement as means to further support NO-mediated endothelial function in such populations.

Reproducibility and Effect of Sampling Depth on Laser Doppler Flowmetry Measures During the Reflex Cutaneous Vasoconstriction Response

During cold exposure, reflex cutaneous vasoconstriction is an important thermoregulatory mechanism that minimizes heat loss. Laser Doppler flowmetry (LDF) is a widely used, non-invasive method of assessing cutaneous microvascular blood flow. However, data on the reproducibility of LDF during a cooling stimulus is limited. Furthermore, various sampling depths of skin measurement are available depending on the type of LDF probe used; however, a comparison of different depths to the same cooling stimulus has not been determined. We hypothesized that LDF probes, particularly those sampling at deeper skin depths, would provide a reproducible measurement of cutaneous microvascular blood flow during whole-body cooling. Fourteen healthy, young adults completed two whole-body cooling bouts, each bout separated by 3-7 days. Participants wore a water-perfused whole-body suit to reduce skin temperature (Tsk) from 34°C to 30.5°C over 30 minutes, and held at 30.5°C for an additional 10 minutes. LDF flux was measured continuously at five forearm sites using 1 VP1-HP Doppler probe, 2 VP7b integrated probes, and 2 VP12 single point Dopplers (Moor Instruments, Axminster, UK) measuring at depths of 4.0 mm, 0.66 mm, and 0.33 mm, respectively. Cutaneous vascular conductance (CVC) was calculated as flux/mean arterial pressure at each 0.5°C reduction in Tsk and at plateau. CVC values were expressed as percent changes from baseline (%ᐃCVCBASELINE). A greater vasoconstriction response was recorded using the VP1-HP Doppler at plateau (34.7 ± 0.6%) compared to the VP7b (31.9 ± 0.5%, p < 0.001) and VP12 (30.3 ± 0.6%, p < 0.001) LDF probes. Additionally, test-retest reproducibility between visits displayed good reproducibility (coefficient of variation <9%) among all three Doppler probes. These data indicate that LDF provides reproducible measurements during reflex cutaneous vasoconstriction at different depths. However, deeper Dopplers, which analyze a greater area of skin, are more likely to discriminate differences in cutaneous microvascular blood flow than those at shallower depths.

Skin Viability and Microvascular Function Under Localised Applications of Heat and Pressure

Soft tissue pressure injuries are localised injuries to surface and deep tissue, caused by sustained compression of skin and muscle between a bony area of the body, and for example, a hospital mattress or medical device. Prolonged cell deformation is known to reduce the structural integrity of the cell cytoskeleton, leading to cascade of cell death, inflammation, oedema and oxidative stress, factors that are likely exacerbated by inadequate blood flow and oxygen delivery. Numerous secondary factors are thought to accelerate this cascade, including systemic hypoxia and changes in tissue temperature. By examining the responses of various skin viability markers, both during and after the application of temperature and pressure stimuli, the present study aims to expand understanding of the secondary factors affecting pressure ulcer onset and progression. In the present study, a custom skin deformation device, with an area of 33cm2, was used to apply a combination of pressures (6, 20 and 40mmHg) and temperatures (23, 33, 38°C) at the sacrum of four healthy volunteers (data collection ongoing). A laser doppler flowmetry probe, embedded into the skin deformation device, was used to measure baseline skin blood flow, skin blood flow under pressure, and reactive hyperaemia (RH) on pressure release. All measurements were calculated as a percentage of heat-induced maximal cutaneous vascular conductance (%CVCmax). Changes in stratum corneum and epidermal hydration were calculated using the difference in tissue electrical capacitance (corneometry) measurements before and after skin deformation. The results indicated a significant difference in loaded skin blood flow between the pressures of 6-20mmHg (p=0.045), and 6-40mmHg (p=0.018), decreasing from 30.5 ± 9.1 %CVCmax to 21.8 ± 9.0 %CVCmax and 17.5 ± 6.7 %CVCmax respectively. Furthermore, there was a significant increase (p=0.030) from 16.9 ± 8.2 %CVCmax to 29.8 ± 5.4 %CVCmax in loaded skin blood flow, between the temperatures of 28-38°C. Finally, blood flow saw a significant (p=0.005) increase on pressure release, from a loaded average of 19.7 ± 8.2 %CVCmax to an unloaded average of 29.0 ± 12.0 %CVCmax, however there was no significant effect of pressure level or temperature on reactive hyperemia. Changes in stratum corneum hydration between 28-33°C (p=0.044), and 28-38°C (p=0.019), increased from 20.8 ± 11.3% to 38.8 ± 12.7% and 48.5 ± 15.5% respectively. Differing pressures and temperatures had no significant effect on epidermal hydration. Initial indications from the present study suggest low local tissue temperature reduces tissue blood flow under pressure, thereby potentially reducing oxygen transport to, and metabolites away from, areas of loaded tissue. However, increased local temperature results in greater moisture accumulation on the surface layer of the cutaneous tissues, potentially resulting in a lower structural integrity. On balance, a neutral skin temperature may be best to balance the harmful effects pressure on tissue viability, but further investigation is required to fully understand the influence of temperature on each aspect of the pressure injury cascade, including cell cytoskeleton integrity, inflammation, and oedema, as well as blood flow dynamics, oxygen delivery, cell metabolism and oxidative stress.

Synchronized research on endothelial dysfunction and microcirculation structure in dorsal skin of rats with type 2 diabetes mellitus.

The aim of this study was to explore changes in the microvascular tone as measured by laser Doppler flowmetry (LDF) and the microcirculation structure of the dorsal skin of rats with type 2 diabetes mellitus. The diabetic rat model was induced by a diet of high-sugar and high-lipid fodder combined with the injection of streptozotocin into the abdominal cavity. Depending on the interval between the development of diabetes and the experiments, the diabetic rats were subdivided into three groups. The evaluation of microvascular tone was based on the amplitude responses of the LDF signal fluctuations in the appropriate frequency range in the dorsal skin of the rats during a thermal test (at 42°C). The nitric oxide (NO) level in plasma was also used as a marker of endothelial dysfunction. Changes in the microcirculation structure in the diabetic rats were estimated by measuring the microvascular density in the choke vessels of the dorsal skin of the rats. The experimental results with respect to red blood cell (RBC)-related parameters showed decreased hematocrit and hemoglobin levels and increased standard deviation of the width of the RBC distribution in three diabetic rats. The increasing fluctuation amplitudes diminished in the endothelial frequency range in response to the thermal test and this was accompanied by abnormal NO levels in plasma of the diabetic groups as compared with healthy rats. A significant reduction in the microvascular density of the choke vessels of the dorsal skin was found only in the diabetic group at the most advanced stage of diabetes in this experiment. Thus, we suggest that endothelial dysfunction occurs in diabetic rats and changes in the microcirculation structure of the dorsal skin occur in a later stage of diabetes development. A. Photograph of measurement method by using a LDF probe and heating device in the dorsal skin of the rat. B. Dorsal skin LDF signals of a healthy rat during the thermal stimuli test. (a) Blood flow signal record for the test. Wavelet filtration of blood flow signal in (b) myogenic range, (c) neurogenic range, and (d) endothelial range.

Effects of cycle periods and pressure amplitudes of alternating pressure on sacral skin blood flow responses

BackgroundThere are no guidelines on selecting alternating pressure (AP) configurations on increasing sacral skin blood flow (SBF). AimThe specific aims were to compare different cycle periods and pressure amplitudes of AP on sacral SBF responses in healthy people to establish the efficacy and safety of the protocols. MethodsTwo studies were tested, including the cycle period study (8 2.5-min vs 4 5-min protocols) and the pressure amplitude study (75/5 vs 65/15 mmHg protocols). Sacral SBF was measured using laser Doppler flowmetry (LDF) in 20 participants. AP loads were randomly applied using an indenter through the rigid LDF probe. Each protocol included a 10-min baseline, 20-min AP and 10-min recovery periods. A 30-min washout period was provided. The SBF response was normalized to the baseline SBF of each condition of each participant. ResultsFor the cycle period study, the 4 5-min cycle protocol partially restored more SBF than the 8 2.5-min cycle protocol at the low-pressure phase (0.87 ± 0.04 vs 0.71 ± 0.03, p < 0.05) and at the high-pressure phase (0.25 ± 0.03 vs 0.19 ± 0.03, p < 0.05). For the pressure amplitude study, the 75/5 mmHg protocol partially restored more sacral SBF than the 65/15 mmHg protocol at the low-pressure phase (0.87 ± 0.1 vs 0.25 ± 0.03, p < 0.05) but not at the high-pressure phase (0.23 ± 0.02 vs 0.21 ± 0.02, non-significant). ConclusionThis study demonstrated that 1) a cycle period of 5 min was better than 2.5 min and 2) a pressure amplitude of 75/5 mmHg was better than 65/15 mmHg. The finding provides insights for selecting the AP configurations for increasing SBF.

A Long Short-Term Memory Network for Vessel Reconstruction Based on Laser Doppler Flowmetry via a Steerable Needle

Hemorrhage is one risk of percutaneous intervention in the brain that can be life-threatening. Steerable needles can avoid blood vessels thanks to their ability to follow curvilinear paths, although knowledge of vessel pose is required. To achieve this, we present the deployment of laser Doppler flowmetry (LDF) sensors as an in-situ vessel detection method for steerable needles. Since the perfusion value from an LDF system does not provide positional information directly, we propose the use of a machine learning technique based on a Long Short-term Memory (LSTM) network to perform vessel reconstruction online. Firstly, the LSTM is used to predict the diameter and position of an approaching vessel based on successive measurements of a single LDF probe. Secondly, a “no-go” area is predicted based on the measurement from four LDF probes embedded within a steerable needle, which accounts for the full vessel pose. The network was trained using simulation data and tested on experimental data, with 75% diameter prediction accuracy and 0.27 mm positional Root Mean Square (RMS) Error for the single probe network, and 77% vessel volume overlap for the 4-probe setup.

Laser Doppler sensing for blood vessel detection with a biologically inspired steerable needle

Puncturing blood vessels during percutaneous intervention in minimally invasive brain surgery can be a life threatening complication. Embedding a forward looking sensor in a rigid needle has been proposed to tackle this problem but, when using a rigid needle, the procedure needs to be interrupted and the needle extracted if a vessel is detected. As an alternative, we propose a novel optical method to detect a vessel in front of a steerable needle. The needle itself is based on a biomimetic, multi-segment design featuring four hollow working channels. Initially, a laser Doppler flowmetry probe is characterized in a tissue phantom with optical properties mimicking those of human gray matter. Experiments are performed to show that the probe has a 2.1 mm penetration depth and a 1 mm off-axis detection range for a blood vessel phantom with 5 mm s−1 flow velocity. This outcome demonstrates that the probe fulfills the minimum requirements for it to be used in conjunction with our needle. A pair of Doppler probes is then embedded in two of the four working channels of the needle and vessel reconstruction is performed using successive measurements to determine the depth and the off-axis position of the vessel from each laser Doppler probe. The off-axis position from each Doppler probe is then used to generate a ‘detection circle’ per probe, and vessel orientation is predicted using tangent lines between the two. The vessel reconstruction has a depth root mean square error (RMSE) of 0.3 mm and an RMSE of 15° in the angular prediction, showing real promise for a future clinical application of this detection system.

Optical Measurements during Deep Brain Stimulation Lead Implantation: Safety Aspects

Background: Intracerebral hemorrhage (ICH) is the most feared complication in deep brain stimulation (DBS) surgery. The aim of the study was to evaluate patient safety and outcome using laser Doppler flowmetry (LDF) as guidance tool during DBS implantations. Methods: An LDF probe adapted for the stereotactic system was used as guide for creation of the trajectory. The microcirculation along 83 preplanned trajectories was measured with the guide during DBS surgery for movement disorders. The microvascular blood flow levels were investigated for all measurement positions. Medical record and postoperative radiology were retrospectively reviewed. Results: Of 2,963 measurement positions, 234 (7.9%) showed at least a doubled blood flow compared to the surrounding tissue. Of these 2.2% had a more than 5 times higher blood flow in front of the probe tip. Along 1 trajectory, a small ICH was detected during surgery. Increased blood flow was more common close to sulci and verticals. Conclusion: Real-time LDF measurement of the microcirculation using a forward-looking probe during DBS surgery can detect blood flow peaks and further minimize the risk of developing ICH. No separate guide tube is necessary as the probe also creates the trajectory for the DBS lead.

LOCAL AND SYSTEMIC EFFECTS OF REPETITIVE SEIZURES

LOCAL AND SYSTEMIC EFFECTS OF REPETITIVE SEIZURES

Time-Frequency Analysis of Increases in Vaginal Blood Perfusion Elicited by Long-Duration Pudendal Neuromodulation in Anesthetized Rats

Female sexual dysfunction (FSD) affects a significant portion of the population. Although treatment options for FSD are limited, neuromodulation for bladder dysfunction has improved sexual function in some women. A few studies have investigated peripheral neuromodulation for eliciting changes in vaginal blood flow, as a proxy for modulating genital sexual arousal, however results are generally transient. Our central hypothesis is that repeated or extended-duration pudendal nerve stimulation can elicit maintained vaginal blood flow increases. Under ketamine anesthesia, the pudendal nerve of 14 female rats was stimulated at varying frequencies (1-100 Hz) and durations (0.15-60 min). Vaginal blood perfusion was measured with a laser Doppler flowmetry probe. Changes in blood perfusion were determined through raw signal analysis and increases in the energy of neurogenic (0.076-0.200 Hz) and myogenic (0.200-0.740 Hz) frequency bands through wavelet analysis. Additionally, a convolution model was developed for a carry-over stimulation effect. Each experiment had significant increases in vaginal blood perfusion due to pudendal nerve stimulation. In addition, there were large concurrent increases in neurogenic and myogenic frequency-band energy in 11/14 experiments, with an average maximal response at 31.3 min after stimulation initiation. An effective stimulation model with a 30-min carry-over effect had a stronger correlation to blood perfusion than the stimulation period itself. Repeated or extended-duration pudendal nerve stimulation can elicit maintained increases in vaginal blood perfusion. This work indicates the potential for pudendal neuromodulation as a method for increasing genital arousal as a potential treatment for FSD.

Optical coherence tomography in the assessment of acute changes in cutaneous vascular diameter induced by heat stress.

There are limited imaging technologies available that can accurately assess or provide surrogate markers of the in vivo cutaneous microvessel network in humans. In this study, we establish the use of optical coherence tomography (OCT) as a novel imaging technique to assess acute changes in cutaneous microvessel area density and diameter in humans. OCT speckle decorrelation images of the skin on the ventral side of the forearm up to a depth of 500 μm were obtained prior to and following 20-25 min of lower limb heating in eight healthy men [30.3 ± 7.6 (SD) yr]. Skin red blood cell flux was also collected using laser Doppler flowmetry probes immediately adjacent to the OCT skin sites, along with skin temperature. OCT speckle decorrelation images were obtained at both baseline and heating time points. Forearm skin flux increased significantly (0.20 ± 0.15 to 1.75 ± 0.38 cutaneous vascular conductance, P < 0.01), along with forearm skin temperature (32.0 ± 1.2 to 34.3 ± 1.0°C, P < 0.01). Quantitative differences in the automated calculation of vascular area densities (26 ± 9 to 49 ± 19%, P < 0.01) and individual microvessel diameters (68 ± 17 to 105 ± 25 μm, P < 0.01) were evident following the heating session. This is the first in vivo within-subject assessment of acute changes in the cutaneous microvasculature in response to heating in humans and highlights the use of OCT as an exciting new imaging approach for skin physiology and clinical research.

Non-invasive spinal cord oxygenation monitoring: validating collateral network near-infrared spectroscopy for thoracoabdominal aortic aneurysm repair.

Near-infrared spectroscopy of the collateral network (cnNIRS) has recently been trialled to monitor real-time tissue oxygenation of the paraspinous vasculature as a surrogate for spinal cord tissue oxygenation. This large animal study was designed to investigate the correlation between cnNIRS and spinal cord oxygenation by comparing it to laser Doppler flowmetry (LDF), a proven method for direct oxygenation and flow assessment. Measurements were performed in seven animals. Four paravertebral cnNIRS optodes were positioned bilaterally at thoracic and lumbar levels to assess tissue oxygenation of the paraspinous vasculature. Paravertebral muscle and spinal cord oxygenation and microcirculatory flow were measured directly using LDF probes. LDF and cnNIRS were compared during consecutive repeated periods of descending aortic cross-clamping for 8 min and recovery by clamp release. Following aortic cross-clamping, lumbar cnNIRS signals instantaneously responded with a decrease to 85 ± 4% within 30 s, and to a minimum of 69 ± 6% after 8 min, returning to baseline values after clamp release within 40 s. Direct lumbar muscle and spinal cord oxygenation assessed by LDF responded analogously to cnNIRS (muscle and spinal cord oxygenation after cross-clamping 11.3 ± 6 and 37.6 ± 22% after 5 and 8 min, respectively). Comparison between lumbar cnNIRS and LDF muscle and spinal cord measurements showed a significant positive correlation (r = 0.51-0.52, P < 0.001). Thoracic cnNIRS signals remained relatively stable throughout the procedure. Lumbar paraspinous muscle oxygenation corresponded to direct spinal cord oxygenation (no significant difference, P = 0.296). These experiments confirm that the paraspinous vasculature in the presented large animal model is directly linked to spinal cord microcirculation and that the regional paraspinous muscle oxygenation status reflects spinal cord tissue oxygenation. As lumbar cnNIRS reproducibly depicts tissue oxygenation of the paraspinous vasculature, it can be used for non-invasive spinal cord oxygenation monitoring in real-time.

Reliability of Skin Blood Flow Measures by Laser‐Doppler Flowmetry

Laser‐Doppler flowmetry (LDF) is a non‐invasive technique often used in combination with local heaters to examine changes in skin blood flow (SkBF). Though customary to normalize cutaneous vascular conductance (CVC) to maximum, CVC normalized to baseline is less common. Accordingly, we sought to evaluate between site measures of SkBF to test the reliability of such practices. Nineteen participants (12 males, 7 females, age 23 ± 3 yr) completed two trials (T1 and T2). Participants rested supine as the dorsal aspect of their dominant forearm was instrumented with two LDF probes and local heaters. Baseline SkBF (in arbitrary units; au) and blood pressure were monitored during which local skin temperature was clamped at 34 °C. Each site was then heated to 42 °C at a rate of 0.2 °C·10 s‐1 for 30 min to attain a maximal SkBF response (i.e., plateau). Blood pressure was measured by automated oscillometry at 10 min intervals. Mean arterial pressure (MAP) was used to calculate CVC (au/MAP). The same procedures were conducted during the second visit. Data were averaged from the two sites and analyzed in raw au's and CVC at baseline and max. Intraclass correlations (ICC) of raw au's at baseline and max were moderately reliable, 0.68 and 0.62, respectively. Additionally, baseline and max CVC were moderately reliable, 0.65 and 0.52, respectively. However, when CVC was expressed as percent change (%Δ) from baseline to max ICC was lower (0.39). These data suggest that indices of SkBF normalized to baseline offer moderate reliability.