Assess Skin Blood Flow Research Articles

Assessing skin blood flow function in people with spinal cord injury using the time domain, time–frequency domain and deep learning approaches

Skin blood flow (SBF) has been assessed using the time domain and time–frequency domain methods. However, these methods require prior knowledge of selecting appropriate parameters for characterizing SBF responses. Deep learning has been successful on classification of medical images, and could be a promising tool for assessing SBF in various pathophysiological conditions. In this study, we proposed a deep learning-based framework for converting 1-dimensional time-series SBF into 2-dimensional time–frequency SBF for convolutional neural networks (CNNs). Thirty-seven participants were recruited into this study, including 21 people with spinal cord injury (SCI) and 16 healthy able-bodied controls. Laser Doppler flowmetry was used to measure sacral SBF. Continuous wavelet transform was used to obtain time–frequency representations of SBF. The whole frequency (WF, 0.0095–2 Hz), high frequency (HF, 0.138–2 Hz), and low frequency (LF, 0.0095–0.138 Hz) regions of the wavelet amplitudes were partitioned into the nonoverlapping patches. Four CNNs including AlexNet, Vgg-19, GoogLeNet, and ResNet-18 were employed to classify the patches. The results showed that the time-domain biphasic thermal index could not differentiate SBF in all groups. Time-frequency wavelet analysis showed differences in myogenic and cardiac controls between people with SCI who were active and sedentary (p < 0.01). CNNs results showed that all participants could be correctly classified based on the WF patches (100% of accuracy) compared to the HF (50–100%) and LF (66.7–100%) patches and five individual oscillation components (50–57.1%). Our study demonstrated that the classifiers could detect subtle changes in SBF function that cannot be revealed by the traditional methods.

Comparison of Antera 3D® and TcPO2 for Evaluation of Blood Flow in Skin.

There is a need for quick skin blood flow tests that can be performed in the wound healing field. Antera 3D® is a compact scanner using multispectral imaging. It can perform quick assessment of skin conditions. The purpose of the present study was to investigate the ability of the Antera 3D® to assess skin blood flow in comparison with transcutaneous partial pressure of oxygen (TcPO2) measurements. This study was conducted on 13 patients with a history of lower extremity ulcers. Measurements of hemoglobin average level (hereafter, Hb score) measured by Antera 3D® and TcPO2 measured by a transcutaneous blood gas monitor were obtained at the same sites on the dorsal foot and lower leg. Differences in Hb score and TcPO2 were analyzed by t-test for each measurement site and for the presence of peripheral arterial disease (PAD). The correlation between TcPO2 and Hb score was analyzed by Pearson's correlation coefficient. Twenty-four limbs were tested. Hb score was higher (P < 0.001) and TcPO2 was lower (P = 0.056) in the dorsal foot compared to the lower leg. In the dorsal foot, Hb score was higher (P = 0.023) and TcPO2 was lower (P = 0.046) in patients with PAD compared to those without PAD. A significant negative correlation (r = -0.68; 95% confidence interval -0.85 to -0.38, P < 0.001) between TcPO2 and Hb score was observed in the dorsal foot. The negative correlation between TcPO2 and Hb score may reflect compensatory peripheral vasodilation due to occlusion or stenosis of central arteries. This study showed that Hb score measured by Antera 3D® may be related to skin blood flow.

Exploring the relationship between capillary refill time, skin blood flow and microcirculatory reactivity during early resuscitation of patients with septic shock: a pilot study.

Capillary refill time (CRT), a costless and widely available tool, has emerged as a promising target to guide septic shock resuscitation. However, it has yet to gain universal acceptance due to its potential inter-observer variability. Standardization of CRT assessment may minimize this problem, but few studies have compared this approach with techniques that directly assess skin blood flow (SBF). Our objective was to determine if an abnormal CRT is associated with impaired SBF and microvascular reactivity in early septic shock patients. Twelve septic shock patients were subjected to multimodal perfusion and hemodynamic monitoring for 24h. Three time-points (0, 1, and 24h) were registered for each patient. SBF was measured by laser doppler. We performed a baseline SBF measurement and two microvascular reactivity tests: one with a thermal challenge at 44°C and other with a vascular occlusion test. Ten healthy volunteers were evaluated to obtain reference values. The patients (median age 70years) exhibited a 28-day mortality of 50%. Baseline CRT was 3.3 [2.7-7.3] seconds. In pooled data analysis, abnormal CRT presented a significantly lower SBF when compared to normal CRT [44 (13.3-80.3) vs 193.2 (99.4-285) APU, p = 0.0001]. CRT was strongly associated with SBF (R2 0.76, p < 0.0001). An abnormal CRT also was associated with impaired thermal challenge and vascular occlusion tests. Abnormal CRT values observed during early septic shock resuscitation are associated with impaired skin blood flow, and abnormal skin microvascular reactivity. Future studies should confirm these results.

Using laser Doppler flowmetry with wavelet analysis to study skin blood flow regulations after cupping therapy.

The purpose of this study was to use laser Doppler flowmetry (LDF) with wavelet analysis to investigate skin blood flow control mechanisms in response to various intensities of cupping therapy. To the best of our knowledge, this is the first study to assess skin blood flow control mechanism in response to cupping therapy using wavelet analysis of laser Doppler blood flow oscillations. Twelve healthy participants were recruited for this repeated-measures study. Three different intensities of cupping therapy were applied using 3 cup sizes at 35, 40, and 45mm (in diameter) with 300mmHg negative pressure for 5minutes. LDF was used to measure skin blood flow (SBF) on the triceps before and after cupping therapy. Wavelet analysis was used to analyze the blood flow oscillations (BFO) to assess blood flow control mechanisms. The wavelet amplitudes of metabolic and cardiac controls after cupping therapy were higher than those before cupping therapy. For the metabolic control, the 45-mm cupping protocol (1.65±0.09) was significantly higher than the 40-mm cupping protocol (1.40±0.10, P<.05) and the 35-mm cupping protocol (1.35±0.12, P<.05). No differences were showed in the cardiac control among the 35-mm (1.61±0.20), 40-mm (1.64±0.24), and 45-mm (1.27±0.25) cupping protocols. The metabolic and cardiac controls significantly contributed to the increase in SBF after cupping therapy. Different intensities of cupping therapy caused different responses within the metabolic control and not the cardiac control.

Assessing Skin Blood Flow and Interface Pressure in Patients With Spinal Cord Injury Provided an Alternating Pressure Overlay: A Cross-sectional Study

This study was conducted among persons with spinal cord injury (SCI) to examine skin blood flow (SBF) and interface pressure (IP) during and after AP overlay use. In this cross-sectional, repeated measures study, persons eligible for participation were clinic outpatients from a large metropolitan area in the midwest United States who were 18 to 65 years old with a SCI with a neurologic level of injury at T10 or above for more than 1 year and used a wheelchair for primary mobility. Persons with a current pressure injury, diabetes mellitus, and/or hypertension or other vascular or pulmonary diseases were excluded. Data regarding age, gender, body mass index (BMI), duration of SCI, and American Spinal Injury Association Impairment Scale scores were collected. The experimental study involved 3 protocols: the AP protocol (participants lay supine for 40 minutes on an operating room [OR] pad with a low-profile AP that used a 10-minute inflation-deflation cycle); the post-AP protocol (participants lay on the 2-inch foam OR pad for 40 minutes), with 30 minutes of rest in between; and the control protocol, comprised of 40-minutes of laying supine on the OR pad. Each participant served as his/her own control. Outcome variables included 1) peak IP (the highest value among adjoining sensors located at the highest pressure point); 2) averaged IP (the averaged value of the sensors), calculated from pressure mapping system data from the sacrum and left heel; and SBF, measured using a laser Doppler flowmetry system. Descriptive analyses were performed for all variables to determine need for parametric or nonparametric analyses. The mean value of peak IP, averaged IP among inflation and deflation cycles of AP, and post-AP and control protocols were compared using repeated measures analysis of variance (ANOVA). Mean SBF among inflation and deflation cycles of AP and post-AP and control protocols were compared using the nonparametric Friedman test, and Wilcoxon signed rank tests were used to compare the SBF responses during the post-loading period. If the results of repeated measures ANOVA or Friedman tests were statistically significant, paired t tests and Wilcoxon signed rank tests were used for pairwise comparison with Bonferroni correction at alpha level 0.0125, respectively. Among the 15 participants (11 men, 4 women; age 41.77 ± 14.49 [range 20-62] years; BMI 26.81 ± 4.13 [range 22-37]; injury duration 17 ± 14.62 [range 1-48] years; mostly (11) African American), peak IP decreased during the AP deflation at sacrum (51.47 ± 30.18 mm Hg vs. 114.13 ± 60.97 mm Hg; P = .002) and heel (26.79 ± 12.91 mm Hg vs. 53.05 ± 18.22 mm Hg; P = 0 .001), and SBF increased at the heel (27.92 ± 32.15 vs. 10.43 ± 11.16 au; P = .006) but was not significant at the sacrum (15.54 ± 15.33 au vs. 11.96 ± 10.26 au, P = .023). Peak IP decreased during post-AP at the sacrum (104.62 ± 58.17 mm Hg; P = .002) but not at the heel (47.69 ± 16.21 mm Hg; P = .097). SBF increased during post-AP at the sacrum (15.78 ± 15.82 au; P = .012) but not at the heel (16.31 ± 29.18 au, P = .427). An AP overlay redistributed IP and increased SBF at the sacrum and heel during use, and its effect 40 minutes after removal was observed only at the sacrum. Studies, including evaluating the lasting effect of AP on weight-bearing tissue protection at different anatomical locations, are needed.

Feasibility of using thermal response to Ka band millimeter wave heating to assess skin blood flow

Objective: Implementation of clinical guidelines for diagnosing peripheral artery disease will demand screening many millions of patients who are considered at-risk. This will require faster, easier screening technologies to identify patients with compromised blood flow to the extremities. Approach: The feasibility of using surface temperature response to Ka band (26.5–40 GHz) near-field irradiation to assess skin blood flow was explored using an animal model. Ears of domestic rabbits were subjected to low-power continuous wave radio frequency heating from an open-ended waveguide (WR-28) at f = 35 GHz. Three flow conditions were evaluated: (1) a baseline flow condition, (2) occluded flow and (3) reactive hyperemia. Surface temperatures were monitored continuously by means of an infrared thermography camera during each 2 min exposure. Main results: Ensemble average results showed significant differences (p < .05) at exposure times 30, 60, 90 and 120 s between baseline and occluded conditions, and between baseline and reactive hyperemia conditions. The occluded condition (N = 12) resulted in an average temperature increase of 21.4 °C ± 3.9 after 2 min, compared with an average increase of 12.1 °C ± 1.6 for baseline conditions (N = 9) and 4.7 °C ± 3.6 for post-occlusion/hyperemic conditions (N = 8). Significance: Results are compared with the results of a simple two parameter mathematical model. These results suggest a method for non-invasive skin blood flow assessment to screen for peripheral artery disease and associated risk of cardiovascular events.

Assessing skin blood flow dynamics in older adults using a modified sample entropy approach.

The aging process may result in attenuated microvascular reactivity in response to environmental stimuli, which can be evaluated by analyzing skin blood flow (SBF) signals. Among various methods for analyzing physiological signals, sample entropy (SE) is commonly used to quantify the degree of regularity of time series. However, we found that for temporally correlated data, SE value depends on the sampling rate. When data are oversampled, SE may give misleading results. To address this problem, we propose to modify the definition of SE by using time-lagged vectors in the calculation of the conditional probability that any two vectors of successive data points are within a tolerance r for m points remain within the tolerance at the next point. The lag could be chosen as the first minimum of the auto mutual information function. We tested the performance of modified SE using simulated signals and SBF data. The results showed that modified SE is able to quantify the degree of regularity of the signals regardless of sampling rate. Using this approach, we observed a more regular behavior of blood flow oscillations (BFO) during local heating-induced maximal vasodilation period compared to the baseline in young and older adults and a more regular behavior of BFO in older adults compared to young adults. These results suggest that modified SE may be useful in the study of SBF dynamics.

Assessment of Skin Microvascular Function and Dysfunction With Laser Speckle Contrast Imaging

In recent years, skin microcirculation has been considered an easily accessible and potentially representative vascular bed to evaluate and understand the mechanisms of microvascular function and dysfunction.1–3 Vascular dysfunction (including impaired endothelium-dependent vasodilation) induced by different pathologies is evident in the cutaneous circulation.4–7 It has been suggested that the skin microcirculation may mirror generalized systemic vascular dysfunction in magnitude and underlying mechanisms.1 Furthermore, minimally invasive skin-specific methodologies using laser systems make the cutaneous circulation a useful translational model for investigating mechanisms of skin physiology and skin pathophysiology induced either by skin disease itself or by other diseases such as vascular, rheumatologic, and pneumologic. To date, the skin has been used as a circulation model to investigate vascular mechanisms in a variety of diseased states, including hypercholesterolemia,8 Alzheimer disease,9 carpal tunnel syndrome,10 schizophrenia,11 hypertension,6 renal disease,12 type 2 diabetes,13 peripheral vascular disease,14 atherosclerotic coronary artery disease,2 heart failure,15 systemic sclerosis,16 obesity,17 primary aging,18,19 and sleep apnea.20 Assessment of skin microvascular function can be done by both invasive and noninvasive techniques. Among noninvasive techniques, laser systems are mainly used.21 The recent development of the laser speckle contrast imaging (LSCI) technique for monitoring skin microvascular function enables its use as a surrogate end point in clinical trials. LSCI allows for noncontact, real-time, and noninvasive monitoring of cutaneous blood flow changes.22,23 Recent evidence has shown that the LSCI technique dramatically reduces the variability of clinical measurements compared with laser Doppler flowmetry (LDF), making the technique a fascinating tool to facilitate microvascular studies in clinical routine.23,24 In this review, we describe …

Comparison between laser speckle contrast imaging and laser Doppler imaging to assess skin blood flow in humans

Objective We tested the linearity between skin blood flux recorded with laser speckle contrast imaging (LSCI) and laser Doppler imaging (LDI), comparing different ways of expressing data. A secondary objective was to test within-subject variability of baseline flux with the two techniques. Methods We performed local heating at 36, 39, 42, and 44 °C on the forearm of healthy volunteers, and measured cutaneous blood flux with LDI and LSCI. Biological zero (BZ) was obtained by occluding the brachial artery. We expressed data as raw arbitrary perfusion units (APUs) and as a percentage increase from baseline (%BL), with and without subtracting BZ. Inter-site variability was expressed as a within subject coefficient of variation (CV). Results Twelve participants were enrolled. Inter-site variability at baseline was lower with LSCI (CV = 9.2%) than with LDI (CV = 20.7%). We observed an excellent correlation between both techniques when data were expressed as raw APUs or APU − BZ (R = 0.90; p < 0.001). The correlation remained correct for %BL ( R = 0.77, p < 0.001), but decreased for %BL − BZ ( R = 0.44, p = 0.003). Bland–Altman plots revealed a major proportional bias between the two techniques. Conclusion This study suggests that skin blood flux measured with LSCI is linearly related to the LDI signal over a wide range of perfusion. Subtracting BZ does not affect this linearity but introduces variability in baseline flux, thus decreasing the correlation when data are expressed as a function of baseline. Finally, systematic bias makes it impossible to assimilate arbitrary perfusion units provided by the two systems.

Evaluation of the Usefulness of Skin Blood Flow Measurements by Laser Speckle Flowgraphy in Pressure-Induced Ischemic Wounds in Rats

Assessment of blood circulation in pressure ulcers can be beneficial for predicting the severity of tissue damage and making the prognosis. Here, we evaluated the usefulness of laser speckle flowgraphy (LSFG) for assessing skin blood flow in pressure-induced ischemic wounds in rats in comparison with skin temperature measurements by thermography, which is commonly used in clinical settings. The blood flow was assessed in 3 groups (control, 1 kg loading, and 10 kg loading for 3 hours), before, immediately after, and on days 1, 2, and 3 after loading. The 10 kg loading induced more severe tissue damage but did not show any distinguishable gross manifestations immediately after releasing the indenter. LSFG detected a significantly reduced blood flow velocity after 10 kg loading compared with 1 kg loading, whereas thermography did not. These results indicate the usefulness of LSFG measurements for assessing tissue circulation in an early phase after tissue damage onset.

Reproducibility and methodological issues of skin post-occlusive and thermal hyperemia assessed by single-point laser Doppler flowmetry

Objective The primary objective of this study was to evaluate 1-week reproducibility of post-occlusive reactive hyperemia (PORH) and local thermal hyperemia (LTH) assessed by single-point laser-Doppler flowmetry (LDF) on different skin sites. We also evaluated spatial reproducibility of both tests on the forearm. Finally, we assessed the influence of mental stress and room temperature variations on PORH and LTH. Methods We performed PORH and LTH assessing skin blood flow on the forearm and on the finger pad with LDF. We repeated the sequence 1 week later. We also performed PORH and LTH during mental stress (Stroop test) and at room temperatures of 21 °C and 27 °C. Data were expressed as cutaneous vascular conductance (CVC), as a function of baseline and as a function of 44 °C vasodilation (%CVC 44). Reproducibility was expressed as within subject coefficients of variation (CV) and intra-class correlation coefficients (ICC). Results Fourteen Caucasian healthy volunteers were recruited. Median age was 25 (2.7) and 50% were female. Median body mass index was 21.2 (5). PORH was reproducible on the finger, whether expressed as raw CVC (CV = 25%; ICC = 0.56) or as %CVC 44 (CV = 24%; ICC = 0.60). However, PORH showed poor reproducibility on the forearm. In the same way, LTH was reproducible on the finger pad when expressed as CVC (CV = 17%; ICC = 0.81) but not on the forearm. Spatial reproducibility was poor on the forearm. Elevated room temperature (27 °C) affected PORH and LTH on the finger pad ( p < 0.05) but not on the forearm. Conclusion Single-point LDF is a reproducible technique to assess PORH and LTH on the finger pad when data are expressed as raw CVC or %CVC 44. On the forearm, however, it shows great inter-day variability, probably due to spatial variability of capillary density. These results highlight the need for alternative techniques on the forearm.

The Effects of Aging on the Skin Blood Response to Warm, Cold, and Contrast Warm and Cold Baths

Objectives: To examine the effects of aging on the ability of contrast baths to increase the circulation in the skin of the foot compared with immersion in a continuous warm water bath of the same temperature as the warm component of the contrast bath.Methods: A laser Doppler flow meter was used to assess skin blood flow on the dorsal and plantar aspects of the foot during immersion in a warm bath (100°F (37.8°C)) compared with contrast baths with a ratio of 3 minutes of warm (100°F (37.8°C)) and 1 minute of cold (60°F (15.6°C)); the cycle was repeated for 16 minutes. Fourteen participants whose average age was 55.1 ± 9.1 years were examined and compared with 12 younger participants whose average age was 23.9 ± 5.8 years.Results: For both groups of participants, the use of alternating hot and cold bath temperatures elicited an increase in skin blood flow above that which was found with warm water immersion alone. The greatest response was in the younger participants. For the older participants, skin blood...

The Effects of Aging on the Skin Blood Response to Warm, Cold, and Contrast Warm and Cold Baths

Objectives: To examine the effects of aging on the ability of contrast baths to increase the circulation in the skin of the foot compared with immersion in a continuous warm water bath of the same temperature as the warm component of the contrast bath.Methods: A laser Doppler flow meter was used to assess skin blood flow on the dorsal and plantar aspects of the foot during immersion in a warm bath (100°F (37.8°C)) compared with contrast baths with a ratio of 3 minutes of warm (100°F (37.8°C)) and 1 minute of cold (60°F (15.6°C)); the cycle was repeated for 16 minutes. Fourteen participants whose average age was 55.1 ± 9.1 years were examined and compared with 12 younger participants whose average age was 23.9 ± 5.8 years.Results: For both groups of participants, the use of alternating hot and cold bath temperatures elicited an increase in skin blood flow above that which was found with warm water immersion alone. The greatest response was in the younger participants. For the older participants, skin blood flow was approximately one-third less than that seen in the younger participants with either continuous warm water immersion or contrast baths. These same results were seen on the dorsal and plantar aspects of the foot, indicating diminished circulation in both areas with aging.Conclusion: We conclude that contrast baths do increase circulation in the skin in the foot of older individuals but the response was less than that of younger people.

Quantification of inspiratory‐induced vasoconstrictive episodes: a comparison of laser Doppler fluxmetry and photoplethysmography

Laser Doppler fluxmetry (LDF) or photoplethysmography (PPG) are frequently used as non-invasive tools to assess skin blood flow. They are both thought to be suitable and interchangeable methods for the detection of sympathetically activated vasoconstrictive episodes that can be provoked by a voluntary deep inspiration (DI), the so-called inspiratory gasp response (IGR). However, a rigorous comparison of the two methods has not been reported in the literature. The aim of this study was to compare the detection of IGR with LDF and PPG. We investigated 14 healthy volunteers (five female, nine male, 25.4 +/- 2.7 years). A PPG probe was applied to the tip of the thumb of the dominant hand, a LDF sensor to the tip of the adjacent index finger. After adaptation and baseline measurements the subjects were asked to perform a DI with time intervals of 90, 60, 30 and 15 s. We found that both methods are useful to detect individual IGR. Overall correlation of IGR amplitude detected with LDF and PPG was significant (r=0.433). Surprisingly, there was a continuous increase of the correlation coefficient from the first (r=0.105) or second (r=-0.184) IGR to the fifth (r=0.727) IGR. This implies that experimental data obtained with PPG and LDF are not equivalent and that one has to be cautious regarding the comparison and interpretation of results obtained with these two different methods.

Altered cutaneous microvascular responses to reactive hyperaemia in coronary artery disease: a comparative study with conduit vessel responses.

Cutaneous microvascular responses to physiological stimuli are currently being investigated as indices of vascular function and to monitor responses to therapy. We attempted to systematically assess various microvascular cutaneous flow indices in response to reactive hyperaemia in control subjects and in patients with coronary artery disease (CAD), and to correlate these with brachial artery flow-mediated dilation (FMD). Groups of 24 healthy controls and 24 subjects with CAD underwent sequential brachial FMD determination in the dominant arm, and laser Doppler imaging to assess skin blood flow in the contralateral arm in response to reactive hyperaemia induced by cuff inflation and release. Laser Doppler values were expressed as: (a) AUC(5 min) (area under the curve over 5 min of release), (b) time to peak response, (c) % reactive hyperaemia, and (d) peak perfusion ratio. As expected, FMD was attenuated in CAD patients compared with controls (1.85+/-4.29% compared with 4.30+/-4.00%; P=0.05). Percentage reactive hyperaemia (CAD, 294+/-290%; controls, 501+/-344%; P=0.04) and the time to peak response as measured by laser Doppler imaging (CAD, 16.84+/-9.61 s; controls, 9.13+/-4.43 s; P=0.001) were significantly different between the CAD and control groups, while AUC(5 min) and the peak perfusion ratio did not show significant differences. Receiver operator curves for sensitivity/specificity analysis suggested that the time to peak response derived by laser Doppler imaging was superior to FMD for the diagnosis of CAD, with an overall specificity of 91.3% (positive predictive value of 89.4%) and a sensitivity of 73.7% (negative predictive value of 77.6%). In conclusion, laser Doppler-derived indices of microvascular flow do not correlate with conduit vessel responses. However, a time to peak response of >10 s as measured by laser Doppler imaging offers superior specificity for the diagnosis of CAD compared with brachial FMD.

Transcutaneous H2 clearance--a new least-invasive method for assessing skin blood flow.

Although there is a wide variety of methods available for measuring or, more precisely, assessing skin blood flow (for a review see Swain and Grant, 1989), the only current method available for measuring skin blood volume flow at a local level, i.e. within areas of a few mm2 and in terms of m1/100g/min, is by use of radioactively labelled freely diffusible indicators (see for example Spence et al., 1985b). Such techniques have proved to be particularly reliable in predicting the outcome of below (versus above) knee amputation in patients with critical lower limb ischaemia (McCollum et al., 1988). However, the technique is invasive (albeit minimally) in that an intracutaneous injection is necessary, it requires the application of a radioactive substance, and above all it is necessary for the patient to remain quite still during the period of recording the clearance, a task which - because of pain - is often difficult for such patients to fulfil.KeywordsSkin Blood FlowRadioactive SubstanceCapillary Blood FlowCuff OcclusionClearance TechniqueThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Cutaneous Blood Flow in Gestational Hypertension and Normal Pregnancy

A laser Doppler flowmeter was used to assess skin blood flow changes in three groups of young subjects: women with gestational hypertension, healthy pregnant women, and healthy non-pregnant women. Responses to four vasoactive stimuli were studied: isometric and cognitive activities, cutaneous post ischemic reactive hyperemia, and local heating. The first two stimuli are vasoconstrictive and were performed on the fingertip, whereas the latter two are vasodilative and were performed on the forearm. The most prominent differences were observed in the isometric test, where the expected decrease, which was indeed registered in non-pregnant women, was almost absent in the healthy pregnant group. The gestational hypertension group had a greater decrease in blood flow than normal pregnancy, but lesser than non-pregnant control subjects. We conclude that although normal pregnancy modifies the response of the skin microvasculature to some vasoactive stimuli, gestational hypertension pushes that response back toward the non-pregnancy state.

Laser Doppler velocimetry vs heater power as indicators of skin perfusion during transcutaneous O2 monitoring.

Laser Doppler velocimetry (LDV) and heater power (HP) were compared as indicators of skin perfusion during transcutaneous oxygen tension (ptcO2) monitoring in adults. The LDV probe was fitted to a Radiometer ptcO2 attachment ring, which was fixed to the forearm. ptcO2, electrode temperature, HP, and LDV measurements were recorded continuously and simultaneously. LDV was more specific and sensitive to changes in cutaneous perfusion. Moreover, changes in perfusion were signalled four to 24 times faster by LDV than by HP. Changes in ptcO2 corresponded to changes in LDV more closely than to changes in HP in all experiments. HP was more specific and sensitive to changes in electrode and air temperatures. Once hyperemia was established at 44 degrees C and the electrode heater was turned off (HP = 0), LDV measurements frequently showed persistence of hyperemia (up to 25 min). Under these circumstances ptcO2 decreased linearly with decreasing electrode temperature in the range of 44-32 degrees C. LDV performance was referenced by monitoring velocity measurements taken on a cylinder revolving at known velocities. We conclude that LDV is a useful adjunct to ptcO2 monitoring and better than HP in assessing skin blood flow. It should enhance quality control of transcutaneous O2 monitoring.