Temperature-dependent interaction between vasoconstrictor and vasodilator mechanisms in human skin

The putative influence of the thermoregulatory state on skin blood-flow responses to various stimuli was studied in 17 healthy subjects exposed to different ambient temperatures. Skin blood flow was monitored by laser Doppler flowmeters and photoelectrical pulse plethysmographs. Stimuli included painful intraneural electrical stimulation (INS) in the median nerve at the wrist, mental stress, arousal stimuli and deep breaths. Intraneural electrical stimulation and mental stress were accompanied by virtually identical changes in skin blood flow, warm subjects responding with cutaneous vasoconstriction whereas cold subjects responded with vasodilatation. Similar but less pronounced responses were obtained with arousal stimuli and single deep breaths. The data indicate that the thermoregulatory state profoundly influences the extent and direction of various cutaneous vasomotor reflex responses. Furthermore, there were differences between responses in hands and feet, suggesting a spatial organization of vasomotor control.     

Continuous measurement of tissue blood flow by laser-Doppler spectroscopy

Laser light scattered from tissue in vivo is broadened in line width as a result of the Doppler shift produced by moving red cells in the microcirculation. A feasibility study was carried out to demonstrate use of this effect to measure and monitor tissue blood flow. Light from a helium-neon laser illuminated a 1-mm area of tissue (human skin or rat renal cortex), and the backscattered light was detected with a photomultiplier. The spectrum of the Doppler beat notes was analyzed directly with a digital spectrum analyzer, or processed by analog circuitry to yield a flow parameter based on the root-mean-square Doppler line width. This parameter was compared with 133Xe washout in the skin of volunteers subjected to UV-induced erythema and the skin of volunteers subjected to UV-induced erythema and was found to vary in an approximately linear manner with skin blood flow. The laser instrument provided continuous monitoring of blood flow fluctuations, including the pulsatile component. The instrument was used to monitor flow in the outer cortex of the rat kidney during administration of norepinephrine, angiotensin, hydralazine, dextran, dopamine, nitroprusside, and angiotensin blocked by saralasin. Dynamic and steady-state responses were consistent with known pharmacology and renal physiology, and with the assumption that vasoconstrictor angiotensin II receptors in the kidney are accessible to blood-borne inhibitors. The laser-Doppler method is a promising tool for rapid monitoring of dynamic changes in tissue perfusion.     

Temporal dynamics of the partial pressure of brain tissue oxygen during functional forepaw stimulation in rats

The partial pressure of tissue oxygen (pO2) was measured in rat somatosensory cortex during periodic electrical forepaw stimulation of either 1 min or 4 s in duration, and correlated with simultaneous laser Doppler flowmetry. For both stimulus durations, a transient decrease in tissue pO2 preceded blood flow changes, followed by a peak in blood flow and an overshoot in tissue pO2. With protracted stimulation, tissue pO2 remained only slightly above pre-stimulus baseline, while blood flow was maintained at a reduced plateau phase. A sustained post-stimulus undershoot in tissue pO2 was observed only for the 1 min stimulus. These findings suggest a complex dynamic relationship between oxygen utilization and blood flow.     

The effect of high- and low-frequency transcutaneous electrical nerve stimulation upon cutaneous blood flow and skin temperature in healthy subjects.

The reported non-analgesic effects of transcutaneous electrical nerve stimulation (TENS) include alterations to the local circulation; however, research in this area has produced equivocal findings. In the present study, the effect of low- (4 Hz) and high-frequency (110 Hz) TENS on forearm skin blood perfusion was assessed using laser Doppler flowmetry. The effect on skin temperature was also assessed using a skin thermistor. Thirty healthy human volunteers were recruited and randomly assigned to a control or one of the two treatment groups. TENS was applied to the skin overlying the median nerve under double-blind conditions for 15 min. Blood flow and skin temperature readings were recorded pre-TENS, during TENS application and continued for 15 min post-TENS application. Analysis of results showed significant increases in blood perfusion during the treatment period in the low-frequency group when compared to the other two groups (P = 0.0106; ANOVA). No significant changes in skin temperature were observed. The results of this study demonstrate that low-frequency TENS produces a local increase in cutaneous blood flow.     

不同强度永磁磁场对成纤维细胞的生物学活性影响研究

目的以磁源空间磁场定量计算为依据,研究正常培养条件下与缺氧培养条件下不同强度永磁磁场对人皮肤成纤维细胞的影响。方法选用人皮肤成纤维细胞,以5×104/mL密度每孔100μL种于96孔板。磁源N面中心实测磁感应强度分别为3.4、5.6、13.8、27.8、52.6、107.0、178.9、292.2 mT的8组磁源,前6组(钐钴合金)尺寸分别为Φ8.0 mm×2.0 mm,后两组(钕铁硼)尺寸分别为Φ8.0 mm×1.5 mm、Φ8.0 mm×2.5 mm,均轴向充磁,即为A、B、C、D、E、F、G、H组。将8组磁场分别作用于正常培养条件下与缺氧培养条件下的人皮肤成纤维细胞,并设对照组(加磁组与非加磁组),3 d后用四甲基偶氮唑盐(MTT)法分别检测细胞活力,做统计学分析。结果两种培养条件下8组不同强度的加磁组人皮肤成纤维细胞的MTT数值与非加磁组的对照组相比较均有升高,正常培养中磁场强度为B、C、D、E、F、G、H组与对照组相比较,差异有统计学意义(P<0.05),且随着磁场强度的增加活性值越高;缺氧培养中磁场强度为G、H组与对照组相比较,差异有统计学意义(P<0.05)。结论实验中选取的永磁磁场对于人皮肤成纤维细胞有增殖和降低损伤的作用。     

Functional evidence for the differential control of superficial and deep blood vessels by sympathetic vasoconstrictor and primary afferent vasodilator fibres in rat hairless skin

We quantitatively investigated sympathetic vasoconstriction and antidromic vasodilation mediated by small-diameter primary afferents on the plantar hairless skin of the hindpaws in Wistar rats using laser Doppler (LD) flowmetry and an infrared thermometer. Sympathetic vasoconstriction was elicited by electrical stimulation of the centrally cut ipsilateral lumbar sympathetic trunk (LST) with 50-s trains at 0.1–20 Hz. Antidromic vasodilation was evoked by electrical stimulation of the dorsal root (DR) L5 with 20-s or 50-s trains at 1–4 Hz. Cutting the LST resulted in increases in skin temperature (SKT) by 6.1±1.0° C (mean±SEM) and in LD flow by 128±20%. Stimulation of the LST resulted in a graded decrease in LD flow and SKT that was most pronounced between 0 and 0.1 Hz. However, DR stimulation evoked a large increase in LD flow but only little change in SKT in rats with sectioned LST. When the DR was stimulated either in animals with intact LST or during continuous stimulation of vasoconstrictor fibres in the sectioned LST, i.e. while baseline temperature was relatively low (26.3±1.1° C), DR stimulation still resulted in large increases in LD flow, but only minor changes in SKT. These results suggest that blood flow through both deep and superficial layers of rat hairless skin is regulated by activity in sympathetic postganglionic vasoconstrictor fibres, whereas small-diameter primary afferent fibres appear to influence predominantly the blood flow through superficial layers of rat plantar skin. Received: 22 April 1997/Accepted: 11 July 1997     

Investigation and improved performance of optical fibre probes in laser Doppler blood flow measurement

Laser Doppler flowmetry with optical-fibre beam transmission is a sensitive fast and convenient method of measuring tissue blood flow. However, its sensitivity can also be a problem because of movement artefacts. This study applies some basic considerations of fibre optics and Rayleigh light scattering to the field of laser Doppler blood flow meters. Practical suggestions are given by which movement arterfacts can be reduced by choice of optical fibres, attention to probe geometry, cladding the fibres to reduce their movements and in the method of application. Experiments which test the normalisation circuitry of laser Doppler instruments are described and the effects of movement artefacts on the interpretation of the pulsatile component of laser Doppler records are also discussed. Probe and fibre line movements cause high-frequency intensity fluctuations due to speckle movement. The intensity fluctuations produce an apparent Doppler shift much greater than the Doppler shift produced by the relative movements of probe and tissue. It has been found that it is important to ensure that the fields of view of the illuminating and detecting fibres do not overlap at the skin surface and that probe contact with the skin surface should be maintained.     

Removal of the skin blood flow artifact in functional near-infrared spectroscopic imaging data through independent component analysis

We investigate whether the functional near-infrared spectroscopic (fNIRS) signal includes a signal from the changing skin blood flow. During a locomotor task on a treadmill, changes in the hemodynamic response in the front-parietal area of healthy human subjects are simultaneously recorded using an fNIRS imaging system and a laser Doppler tissue blood flow meter. Independent component analysis (ICA) for fNIRS signals is performed. The skin blood flow changes during locomotor tasks on a treadmill. The activated spatial distribution of one of the components separated by ICA reveals an overall increase in fNIRS channels. To evaluate the uniformity of the activated spatial distribution, we define a new statistical value-the coefficient of spatial uniformity (CSU). The CSU value is a highly discriminating value (e.g., 2.82) compared with values of other components (e.g., 1.41, 1.10, 0.96, 0.61, and 0.58). In addition, the independent component signal corresponding to the activated spatial distribution is similar to changes in skin blood flow measured with the laser Doppler tissue blood flow meter. The coefficient of correlation indicates strong correlation. Localized activation areas around the premotor and medial somatosensory cortices are shown more clearly by eliminating the extracted component.     

Responses of cortical cerebral blood flow produced by stimulation of cervical sympathetic trunks are well maintained in aged rats

Responses of cortical cerebral blood flow (CBF) in the parietal cortex following electrical stimulation of cervical sympathetic trunks (CSTs) were compared in healthy adult (4-6 months old) and healthy aged (28-32 months old) Fischer-344 rats anesthetized with urethane. The cortical CBF was continuously monitored using laser Doppler flowmetry (LDF). The electrical stimulation of CSTs with supramaximum intensity caused the frequency-dependent initial-increase and late-decrease responses of cortical CBF in both adult and aged rats. There were no significant differences in magnitude and time course of the responses of the cortical CBF with the comparable frequencies of the electrical stimulation of the CSTs between the adult and the aged rats. These evidences suggest that the neural control of the cortical CBF by the sympathetic nerves is quite well maintained in aged rats.     

Blood flow changes in the dental pulp of the cat and rat measured simultaneously by laser Doppler flowmetry and local 125I clearance

Blood flow changes in the dental pulp of lower canine teeth of mature cats and incisors of mature rats were investigated with simultaneous laser Doppler flowmetry and local 125I-clearance (wash-out) during electrical sympathetic stimulation, efferent stimulation of n. alveolaris inferior (IAN) (cats) and i.a. infusions of substance P (SP) (cats). Stimulation (1-4 Hz, 4 V., 1.5 ms) of the cervical sympathetic trunk produced frequency-dependent decreases in both laser Doppler output and disappearance rate of iodine tracer from the dental pulp. For the effects of sympathetic stimulation, the correlation (r2) between the results obtained by the two methods was 0.89 (12 observations, six animals). Blood flow measurements by both methods were increased following i.a. infusions of SP (r2 = 0.64, six observations, three animals). However, upon stimulation of IAN (10 Hz 10 V, 5 ms) the laser Doppler flow values showed an increase while the local 125I clearance rate was unaffected or even decreased. The discrepancy between the results obtained following IAN stimulation indicates that the two methods reflect blood flow changes in different parts of the pulpal vascular bed and that the flow is unevenly distributed to these parts during antidromic IAN stimulation. The laser Doppler flowmetry seems to reflect the total blood flow in the coronal pulp and therefore this non-invasive method may be useful for monitoring blood flow changes in the tooth.     

不同强度静磁场对成骨细胞细胞骨架改建的影响

背景：静磁场对成骨细胞增殖活性、细胞因子分泌及碱性磷酸酶表达等功能活性影响的机制尚不清楚。 目的：观察不同强度静磁场加载对成骨细胞骨架改建和细胞骨架蛋白表达的影响。 方法：取新生24 h内SD大鼠颅骨进行成骨细胞的培养和鉴定。采用静磁场加载装置对体外培养的成骨细胞进行0,8,50,160 mT的静磁场加载,分别于静磁场加载24,48,72 h应用BODYPY-Phaloidin进行成骨细胞骨架染色,激光扫描共聚焦显微镜和图像处理软件Image J测定细胞骨架蛋白的荧光强度。 结果与结论：8,50,160 mT静磁场加载24,48,72 h,荧光标记的成骨细胞骨架蛋白向细胞核周围集中,荧光强度增强(P < 0.05),其中经50 mT静磁场加载的成骨细胞骨架蛋白的荧光最强。说明一定强度的静磁场可以影响成骨细胞骨架的改建和重组。     

New system for neonatal hearing screening based on auditory steady state responses

Carbonized rubber electrodes were tested extensively when they were first developed 30 years ago, but modern carbonized rubber electrodes have not received the type of scrutiny that the first electrodes received. Modern electrodes differ from the original electrodes in that they come with a self-adhesive electrode gel called hydrogel as part of their composition. The present study was undertaken to examine the current distribution and impedance characteristics of five brands of carbonized rubber electrodes and to examine the current distribution between electrodes during electrical stimulation in six subjects. Several different electrode sizes were tested between 3 and 10 cm. The current flow between the electrodes was determined by measuring the voltage across the skin on human subjects in 15 discrete locations between the electrodes. Blood flow was also measured between the electrodes with a laser Doppler flow meter to assess the physiological effect of current distribution on the skin at several skin temperatures. The results of these studies showed that at low currents, such as is used in TENS, very little current is actually applied through the skin due to the high impedance of the electrodes. At current levels normally used for electrical stimulation for functional movement, while current flow is better in most electrodes, it is very uneven, resulting in high current density in the centre of the electrodes and a fall off of at least 50% in current intensity at the edges of the electrode. There was very little difference in current density between small and large electrodes due to the high current density in the centre. Skin blood flow altered the movement of current between the electrodes and also may contribute to electrode performance. The implication of these studies is that electrode design needs to be altered for better current distribution, especially at low stimulation currents.     

Current distribution under electrodes in relation to stimulation current and skin blood flow: are modern electrodes really providing the current distribution during stimulation we believe they are?

Carbonized rubber electrodes were tested extensively when they were first developed 30 years ago, but modern carbonized rubber electrodes have not received the type of scrutiny that the first electrodes received. Modern electrodes differ from the original electrodes in that they come with a self-adhesive electrode gel called hydrogel as part of their composition. The present study was undertaken to examine the current distribution and impedance characteristics of five brands of carbonized rubber electrodes and to examine the current distribution between electrodes during electrical stimulation in six subjects. Several different electrode sizes were tested between 3 and 10 cm. The current flow between the electrodes was determined by measuring the voltage across the skin on human subjects in 15 discrete locations between the electrodes. Blood flow was also measured between the electrodes with a laser Doppler flow meter to assess the physiological effect of current distribution on the skin at several skin temperatures. The results of these studies showed that at low currents, such as is used in TENS, very little current is actually applied through the skin due to the high impedance of the electrodes. At current levels normally used for electrical stimulation for functional movement, while current flow is better in most electrodes, it is very uneven, resulting in high current density in the centre of the electrodes and a fall off of at least 50% in current intensity at the edges of the electrode. There was very little difference in current density between small and large electrodes due to the high current density in the centre. Skin blood flow altered the movement of current between the electrodes and also may contribute to electrode performance. The implication of these studies is that electrode design needs to be altered for better current distribution, especially at low stimulation currents.     

Three-electrode method to study event-related responses in skin electrical potential,admittance and blood flow

To investigate a broader spectrum of responses to the activity of efferent sympathetic nerve endings in blood vessels and sweat glands of the human palmar skin, we have developed a method to measure skin potential, skin unipolar electrical admittance (conductance and capacitance), skin blood flow, and skin temperature simultaneously at the same site of human palmar skin. The electrical variables were measured with a specially designed probe and a three electrode lock-in amplifier measuring system. The aim of the paper is to evaluate this method and its potential application in clinical work. The experimental results from five subjects during 5 min of baseline condition and during repeated acoustic stimulation are presented. The skin temperature was displayed digitally. During basal condition the activities in skin electrical variables and in blood vessel vasomotion were largely independent (asynchronous), whereas efferent sympathetic discharges due to stimulation were followed by parallel evoked responses in skin admittance, skin potential and skin blood flow. Habituation to the repeated stimuli occurred differently in the four variables.     

A multi-channel stimulator and electrode array providing a rotating current whirlpool for electrical stimulation of wounds

When electrical stimulation is used on wounds, the electrical current has difficulty penetrating areas where there is necrotic tissue. Further, for an irregularly shaped wound, current distribution is poor in some areas of the wound since conventional two-electrode delivery systems provide the greatest current in a line directly between the electrodes. A new stimulator and electrode system is described which uses three electrodes spaced around a wound to disperse current more evenly. The stimulator senses tissue impedance and then redirects current by altering its Thevenin's output impedance for each electrode; each of the three electrodes becomes the active one in sequence while the remaining are the sink electrodes. Eight subjects were examined to test the stimulator. Electrical stimulation was applied to the skin above the quadriceps muscle at currents of 15 mA in six subjects without wounds and in two subjects with wounds. The relationship between electrode position and current dispersion on the skin was examined with a two-electrode vs. a three-electrode system to set stimulation parameters for the computer. The results showed that the three-electrode system could (1) detect areas of the skin with high impedance; (2) compensate by altering the Thevenin's output impedance at each of the three electrodes to shift current to high impedance areas; (3) provide uniform current across the skin as assessed by skin current and blood flow measurements with a laser Doppler flow imager.     

Axon reflex vasodilatation in human skin measured by a laser Doppler technique.

This study was designed to investigate whether or not an objective method to measure a blood flow value by laser Doppler technique is possible to study the mechanism of an axon reflex vasodilatation elicited by i.d. injection of histamine or substance P into human skin. The probe of laser Doppler flowmeter was placed 10 mm apart from the injection site in the ventral forearm. The blood flow increased after the i.d. injection of histamine, substance P, but not after injection of Ringer solution. Penetration by the hypodermic needle produced an increase in the blood flow, but this increase was masked by the injection of the Ringer solution. The histamine- or substance P-induced blood flow increase was dose-dependent in both duration and intensity. Pretreatment with diphenhydramine ointment or xylocaine jelly 1 h prior to i.d. injection of histamine or substance P significantly attenuated the blood flow increase elicited by either vasoactive substance. Pretreatment of the skin with capsaicin (1% alcoholic solution) for 2 or 3 days markedly reduced the histamine- or substance P-induced blood flow increase. These results show that the measurement of cutaneous blood flow by laser Doppler flowmeter is useful in studying the mechanism of vasoactive substances-induced axon reflex vasodilatation.     

A multi-channel stimulator and electrode array providing a rotating current whirlpool for electrical stimulation of wounds

When electrical stimulation is used on wounds, the electrical current has difficulty penetrating areas where there is necrotic tissue. Further, for an irregularly shaped wound, current distribution is poor in some areas of the wound since conventional two-electrode delivery systems provide the greatest current in a line directly between the electrodes. A new stimulator and electrode system is described which uses three electrodes spaced around a wound to disperse current more evenly. The stimulator senses tissue impedance and then redirects current by altering its Thevenin's output impedance for each electrode; each of the three electrodes becomes the active one in sequence while the remaining are the sink electrodes. Eight subjects were examined to test the stimulator. Electrical stimulation was applied to the skin above the quadriceps muscle at currents of 15 mA in six subjects without wounds and in two subjects with wounds. The relationship between electrode position and current dispersion on the skin was examined with a two-electrode vs. a three-electrode system to set stimulation parameters for the computer. The results showed that the three-electrode system could (1) detect areas of the skin with high impedance; (2) compensate by altering the Thevenin's output impedance at each of the three electrodes to shift current to high impedance areas; (3) provide uniform current across the skin as assessed by skin current and blood flow measurements with a laser Doppler flow imager.     

Measurement of digital blood flow using the laser Doppler,impedance and strain-gauge methods

Digital volume changes and blood flow have been measured with impedance and strain-gauge plethysmography as well as with laser Doppler flowmetry. A good agreement was found between the impedance and strain-gauge flow measurements with a correlation coefficient of 0·905. The laser Doppler method recorded minor changes in finger skin blood flow following changes in posture from 30 cm below heart level to 60 cm above heart level. This result can be explained as a consequence of the limited penetration depth of laser light into the skin or as a sign of autoregulation of skin blood flow. In these experiments the total blood flow to the finger underwent major changes.     

Comparison of laser speckle and laser Doppler perfusion imaging: Measurement in human skin and rabbit articular tissue

Laser Doppler perfusion imaging (LDI) is currently used in a variety of clinical applications, however, LDI instruments produce images of low resolution and have long scan times. A new optical perfusion imager using a laser speckle measurement technique and its use for in vivo blood flow measurements are described. Measurements of human skin and surgically exposed rabbit tissue made using this instrument were compared with a commercial laser Doppler perfusion imaging instrument. Results from blood flow measurements showed that the laser speckle imager measured an 11–67% decrease in blood flow under arterial occlusion. Under similar conditions, the laser Doppler imager measured blood flow decreases of 21–63%. In comparison with LDI, it was observed that the higher temporal resolution of the laser speckle imager was more sensitive to measuring the hyperaemic response immediately following occlusion. This in vivo study demonstrated some of the several advantages laser speckle imaging has over conventional LDI, making the new instrument more versatile in a clinical environment.     

Heterogeneous blood flow response in the foot on dependency,assessed by laser Doppler perfusion imaging

The exact nature of the decrease in foot skin blood flow seen after a change in posture remains unsettled. This mechanism has previously been examined by non-invasive techniques such as the laser Doppler perfusion monitor (laser Doppler flowmetry). Taking into account the shortcomings of laser Doppler perfusion monitoring when applied to the determination of skin blood flow, which normally shows substantial heterogeneity, we have applied an emerging technology, the laser Doppler perfusion imager (LDPI). This technique provides a more comprehensive picture of the blood flow distribution in the skin, as it maps skin blood flow over a surface area (120×120 mm, 4096 measurement sites). It was used to examine if the reduction in tissue perfusion or the alterations in flow distributions seen after a change in posture (supine to dependency) could be fully explained by an increase in venous pressure (venous stasis of 50 mmHg) or if the data suggest a complementary mechanism. Skin blood flow of the forefoot decreased from 0.60 V (volt) (median) during rest to 0.40 and 0.38 V during venous stasis and dependency, respectively. Although almost identical median values were obtained during stasis and dependency, the flow distributions were different, with a loss of high flow values during venous stasis. Biological zero was 0.24 V. As the LDPI technique readily records skin perfusion during variations in venous stasis and posture, as well as information on flow distribution changes, it appears promising for future application in stimuli-response studies of skin blood flow. The difference in flow distribution seen between increased venous pressure and dependency suggests an additive regulatory mechanism to the veni-vasomotor reflex during a change in posture.