Mechanisms and modifiers of reflex induced cutaneous vasodilation and vasoconstriction in humans

The role of C-afferents in mediating neurogenic vasodilatation in plantar skin after acute sciatic nerve injury in rats

Background

Vasomotor regulation of dermal blood vessels, which are critical in the function of the skin in thermoregulatory control, involves both neural and non-neural mechanisms. Whereas the role of sympathetic nerves in regulating vasomotor activities is comprehensively studied and well recognized, that of sensory nerves is underappreciated. Studies in rodents have shown that severance of the sciatic nerve leads to vasodilatation in the foot, but whether sympathetic or sensory nerve fibers or both are responsible for the neurogenic vasodilatation remains unknown.

Results

In adult Sprague–Dawley rats, vasodilatation after transection of the sciatic nerve gradually diminished to normal within 3–4 days. The neurotmesis-induced neurogenic vasodilatation was not detectable when the sciatic nerve was chronically deafferentated by selective resection of the dorsal root ganglia (DRGs) that supply the nerve. Specific activation of C-afferents by intra-neural injection of capsaicin resulted in neurogenic vasodilatation to a magnitude comparable to that by neurotmesis, and transection of the sciatic nerve pre-injected with capsaicin did not induce further vasodilatation.

Conclusions

Our results collectively indicate that vasodilatation after traumatic nerve injury in rats is predominantly mediated by C-fiber afferents.

Current Knowledge on the Vascular Effects of Menthol

Menthol is a monoterpene alcohol, widely used in several food and healthcare products for its particular odor and flavor. For some decades, menthol has been known to act on the vasculature directly in the endothelium and vascular smooth muscle, with recent studies showing that it also evokes an indirect vascular response via sensory fibers. The mechanisms underlying menthol's vascular action are complex due to the diversity of cellular targets, to the interplay between signaling pathways and to the variability in terms of response. Menthol can evoke either a perfusion increase or decrease in vivo in different vascular territories, an observation that warrants a critical discussion. Menthol vascular actions in vivo seem to depend on whether the vascular territory under analysis has been directly provoked with menthol or is located deep/distant to the application site. Menthol increases perfusion of directly provoked skin regions due to a complex interplay of increased nitric oxide (NO), endothelium-derived hyperpolarization factors (EDHFs) and sensory nerve responses. In non-provoked vascular beds menthol decreases perfusion which might be attributed to heat-conservation sympathetically-mediated vasoconstriction, although an increase in tissue evaporative heat loss due the formulation ethanol may also play a role. There is increasing evidence that several of menthol's cellular targets are involved in cardiovascular diseases, such as hypertension. Thus menthol and pharmacologically-similar drugs can play important preventive and therapeutic roles, which merits further investigation.

The immediate effects of kinesiology taping on cutaneous blood flow in healthy humans under resting conditions: A randomised controlled repeated-measures laboratory study

BACKGROUND

Kinesiology taping (KT) is used in musculoskeletal practice for preventive and rehabilitative purposes. It is claimed that KT improves blood flow in the microcirculation by creating skin convolutions and that this reduces swelling and facilitates healing of musculoskeletal injuries. There is a paucity of physiological studies evaluating the effect of KT on cutaneous blood microcirculation.

OBJECTIVES

The purpose of this parallel-group controlled laboratory repeated measures design study was to evaluate the effects of KT on cutaneous blood microcirculation in healthy human adults using a dual wavelength (infrared and visible-red) laser Doppler Imaging (LDI) system. KT was compared with rigid taping and no taping controls to isolate the effects associated with the elasticity of KT.

METHODS

Forty-five healthy male and female human adults were allocated to one of the three interventions using constrained randomisation following the pre-intervention measurement: (i) KT (ii) ST (standard taping) (iii) NT (no taping). Cutaneous blood perfusion was measured using LDI in the ventral surface of forearm at pre-intervention, during-intervention and post-intervention in a normothermic environment at resting conditions.

RESULTS

Mixed ANOVA of both infrared and visible-red datasets revealed no statistically significant interaction between Intervention and Time. There was statistically significant main effect for Time but not Intervention.

CONCLUSION

KT does not increase cutaneous blood microcirculation in healthy human adults under resting physiological conditions in a normothermic environment. On the contrary, evidence suggests that taping, regardless of the elasticity in the tape, is associated with immediate reductions in cutaneous blood flow.

Historical reviews of the assessment of human cardiovascular function: interrogation and understanding of the control of skin blood flow

Several techniques exist for the determination of skin blood flow that have historically been used in the investigation of thermoregulatory control of skin blood flow, and more recently, in clinical assessments or as an index of global vascular function. Skin blood flow measurement techniques differ in their methodology and their strengths and limitations. To examine the historical development of techniques for assessing skin blood flow by describing the origin, basic principles, and important aspects of each procedure and to provide recommendations for best practise. Venous occlusion plethysmography was one of the earliest techniques to intermittently index a limb’s skin blood flow under conditions in which local muscle blood flow does not change. The introduction of laser Doppler flowmetry provided a method that continuously records an index of skin blood flow (red cell flux) (albeit from a relatively small skin area) that requires normalisation due to high site-to-site variability. The subsequent development of laser Doppler and laser speckle imaging techniques allows the mapping of skin blood flow from larger surface areas and the visualisation of capillary filling from the dermal plexus in two dimensions. The use of iontophoresis or intradermal microdialysis in conjunction with laser Doppler methods allows for the local delivery of pharmacological agents to interrogate the local and neural control of skin blood flow. The recent development of optical coherence tomography promises further advances in assessment of the skin circulation via three-dimensional imaging of the skin microvasculature for quantification of vessel diameter and vessel recruitment.

Thermoregulation in the Aging Population and Practical Strategies to Overcome a Warmer Tomorrow

As global temperatures continue to rise, improving thermal tolerance in the aged population is crucial to counteract age-associated impairments in thermoregulatory function. Impairments in reflex cutaneous vasodilation and sweating response can augment the vulnerability of older adults to heat-related injuries following exposure to heat stress. Mechanisms underlying a compromised cutaneous vasodilation are suggested to include reduced sympathetic neural drive, diminished cholinergic co-transmitter contribution, and altered second messenger signaling events. On the other hand, impairments in sweating response are ascribed to reduced sweat gland cholinergic sensitivity and altered cyclooxygenase and nitric oxide signaling. Several practical mitigation strategies such as exercise, passive heating, and behavioral adaptations are proposed as means to overcome heat stress and improve thermal tolerance in the aged. Aerobic exercise training is shown to be amongst the most effective ways to enhance thermoregulatory function. However, in elderly with limited exercise capability due to chronic diseases and mobility issues, passive heating can serve as a functional alternative as it has been shown to confer similar benefits to that of exercise training. Supplementary to exercise training and passive heating, behavioral adaptations can be applied to further enhance the heat-preparedness of the aged.

Influences of hypobaric hypoxia on skin blood flow and sweating responses during exercise in neutral and hot environments

Exposure to hot environments augments cutaneous vasodilation and sweating during exercise compared with these responses in cooler environments. The effects of hypobaric hypoxia on these responses are less clear, as are the effects of heat and simulated altitude combined. We evaluated the individual and potential additive effects of environmental heat and hypobaric hypoxia on skin blood flow and sweating responses during exercise. Thirteen volunteers (11 M, 2 F; age 25.3 ± 6.1 yr; height 177 ± 9 cm; weight 81.2 ± 16.8 kg) completed 30 min of steady-state (SS) exercise on a cycle ergometer at 50% V̇o_2peak during four separate conditions: 1) sea level thermoneutral (SLTN; 250 m, 20°C, 30-50% RH), 2) sea level hot (SLH; 250 m, 35°C, 30% RH), 3) simulated altitude thermoneutral (ATN; 3,000 m, 20°C, 30-50% RH), and 4) simulated altitude hot (AH; 3,000 m, 35°C, 30% RH). Skin blood flow and local sweating rate (LSR) were recorded on the ventral forearm. During exercise, SS cutaneous vascular conductance in AH (63 ± 31% peak) and SLH (52 ± 19% peak) were significantly higher than both SLTN (20 ± 9% peak, P < 0.001) and ATN (25 ± 12% peak, P < 0.05) but were not different from each other (P > 0.05). SS LSR was similarly increased in the hot environments but unaffected by simulated altitude. We propose that multiple antagonistic mechanisms during exposure to 3,000-m simulated altitude result in no net effect on skin blood flow or sweating responses during exercise in thermoneutral or hot environments.

Mechanisms of Blood Flow Regulation in the Skin during Stimulation of the Spinal Cord in Humans

Changes in the blood flow in the shin skin were observed by laser Doppler flowmetry after transcutaneous electrical spinal cord stimulation (TSCS) by subthreshold bipolar pulses with a frequency of 30 Hz in 12 healthy subjects. It was found that TSCS in the area of the T₁₁ and L₁ vertebrae led to a significant increase in skin blood flow. The microcirculation rate increased by more than 85% relative to the baseline at a stimulus intensity of 90% of the motor threshold. Cutaneous blood flow activization by TSCS is implemented mainly through the antidromic stimulation of sensory nerve fibers. Nitric oxide (NO) is an important mediator that contributes to vasodilation and increase in cutaneous blood flow upon TSCS. NO is predominantly of endothelial origin.

Thermal and cardiovascular responses and thermal sensation during hot-water bathing and the influence of room temperature

The aim of the present study was to clarify physical risks during hot-water bathing by measuring thermal and cardiovascular responses and thermal sensation. Young men and women (n = 7 and 5, respectively) participated in the present study, which consisted of two trials mimicking bathing behavior at room temperature of 25 °C and 15 °C. Participants bathed in 41 °C water for 20 min to the subclavian level. Before bathing, participants rested fully clothed for 15 min and then rested for 15 min without clothes. After bathing, they rested without clothes for 15 min and afterwards rested fully clothed for another 15 min. Tympanic temperature (T_ty), heart rates (HR), mean skin temperature (T_sk), mean arterial pressure (MAP), and laser-Doppler flow at the chest and forehead (LDF_head and LDF_chest) were evaluated. Thermal perception was assessed with a visual analogue scale. Mean T_sk in the 15 °C trial decreased during the period without clothing while MAP increased. The value remained unchanged in the 25 °C trial. During bathing, T_ty, mean T_sk, HR, LDF_head, and LDF_chest increased in both trials, and MAP decreased to similar levels. Relative change in LDF_chest was greater in the 15 °C trial than in the 25 °C trial. Participants felt cold when they were without clothes at 15 °C; however, the thermal perception during bathing was similar between the two trials. Greater changes in cardiovascular and thermal responses were observed during the bathing behavior. In addition, bathing in cold room augmented the changes, which may induce some physical risks during bathing.

Oligonucleotide Microarrays Identified Potential Regulatory Genes Related to Early Outward Arterial Remodeling Induced by Tissue Plasminogen Activator

Constrictive vascular remodeling limiting blood flow, as well as compensatory outward remodeling, has been observed in many cardiovascular diseases; however, the underlying mechanisms regulating the remodeling response of the vessels remain unclear. Plasminogen activators (PA) are involved in many of the processes of vascular remodeling. We have shown previously that increased levels of tissue-type PA (tPA) contributes to outward vascular remodeling. To elucidate the mechanisms involved in the induction of outward remodeling we characterized changes in the expression profiles of 8799 genes in injured rat carotid arteries 1 and 4 days after recombinant tPA treatment compared to vehicle. Periadventitial tPA significantly increased lumen size and vessel area, encompassed by the external elastic lamina, at both one and 4 days after treatment. Among 41 differentially expressed known genes 1 day after tPA application, five genes were involved in gene transcription, five genes were related to the regulation of vascular tone [for example, thromboxane A2 receptor (D32080) or non-selective-type endothelin receptor (S65355)], and eight genes were identified as participating in vascular innervation [for example, calpain (D14478) or neural cell adhesion molecule L1 (X59149)]. Four days after injury in tPA-treated arteries, four genes, regulating vascular tone, were differentially expressed. Thus, tPA promotes outward arterial remodeling after injury, at least in part, by regulating expression of genes in the vessel wall related to function of the nervous system and vascular tone.

Evaluation of the temperature of posterior lower limbs skin during the whole body vibration measured by infrared thermography: Cross-sectional study analysis using linear mixed effect model

BACKGROUND

Whole body vibration exercise (WBVE) has been shown to improve muscular strength and power, and increase peripheral blood flow. The aim of this study was to evaluate the behavior of the skin temperature (Tsk) on regions of the lower limbs from an acute bout of WBVE.

METHODS AND FINDINGS

Cross-sectional study approved by local ethics committee (Certificado de Apresentação para Apreciação Ética-CAAE-19826413.8.0000.5259) and Trial registration (Registro Brasileiro de Ensaios Clínicos-REBEC-RBR-738wng). Using Infrared thermography (IRT), Tsk and thermal symmetry of the posterior lower extremities (thigh, knee, calf and heel) were examined in 19 healthy participants. IRT was assessed during 60-second WBVE exposures of 0, 30 and 50 Hz. From the adjusted linear mixed effects model, vibration frequency, time and regions of the lower extremity were significant (p<0.001). However, the variable laterality was not significant (p = 0.067) and was excluded from the adjusted statistical model. The adjusted model was significant (p<0.00001) and all variables in the model were significant (p<0.01) indicating that Tsk decreases with time, independently of the vibration frequency. The value of the Pseudo-R-Squared for the model was 0.8376. The presented mathematical model of the current study may be useful to justify the patterns observed for all vibration frequencies between and 0 and 50 Hz. The main limitations of the study were the reduced time of the intervention and not having evaluated other regions of the body.

CONCLUSIONS

The acute exposure of 60-second mechanical vibration has effect on the behavior of Tsk of the posterior region of the lower limbs, which is likely to be associated with a decrease on the blood flow due to WBVE. It is speculated that during WBVE a greater supply of blood is required where the body responds by shunting blood flow from the skin to working muscle in the first seconds of exercise. Further investigative work is required to verify this hypothesis.

Effect of heat stress on vascular outcomes in humans

In addition to its role as an environmental stressor, scientists have recently demonstrated the potential for heat to be a therapy for improving or mitigating declines in arterial health. Many studies at both ends of the scientific controls spectrum (tightly controlled, experimental vs. practical) have demonstrated the beneficial effects of heating on microvascular function (e.g., reactive hyperemia, cutaneous vascular conductance); endothelial function (e.g., flow-mediated dilation); and arterial stiffness (e.g., pulse-wave velocity, compliance, β-stiffness index). It is important to note that findings of beneficial effects are not unanimous, likely owing to the varied methodology in both heating protocols and assessments of outcome measures. Mechanisms of action for the effects of both acute and chronic heating are also understudied. Heat science is a very promising area of human physiology research, as it has the potential to contribute to approaches addressing the global cardiovascular disease burden, particularly in aging and at risk populations, and those for whom exercise is not feasible or recommended.

Relationship between climate and hemodynamics according to echocardiography

Studies performed in controlled laboratory conditions have shown that environmental thermal application may induce various circulatory changes. We aimed to demonstrate the effect of local climate on hemodynamics according to echocardiography. Echocardiographic studies conducted in ambulatory patients, 18 yr of age or older, between January 2012 and July 2016, at our medical center, for whom climate data on the day of the echocardiogram study were available, were retrospectively included in case climate data. Discomfort index, apparent temperature, temperature-humidity index, and thermal index were computed. Echocardiograms conducted in hotter months (June-November) were compared with those done in colder months (December-May). The cohort consisted of 11,348 individuals, 46.2% women, and mean age of 57.9 ± 18.1 yr. Climate indexes correlated directly with stroke volume ( r = 0.039) and e' (lateral r = 0.047; septal r = 0.038), and inversely with systolic pulmonary artery pressure (SPAP; r = -0.038) (all P values < 0.05). After adjustment for age and sex, echocardiograms conducted during June-November had a lower chance to show e' septal < 7 cm/s (odds ratio 0.88, 95% confidence interval 0.78-0.98, P = 0.017) and SPAP > 40 mmHg (odds ratio 0.81, 95% confidence interval 0.67-0.99, P = 0.04) compared with those conducted in other months. The authors concluded that climate may affect hemodynamics, according to echocardiographic assessment in ambulatory patients. NEW & NOTEWORTHY In the present study, we examined 11,348 individuals who underwent ambulatory echocardiography. Analyses of the echocardiographic studies demonstrated that environmental thermal stress, i.e., climate, may affect hemodynamics. Most notably were the effects on diastolic function. Higher values of mitral e', stroke volume, as well as ejection fraction, and lower values of systolic pulmonary artery pressure and tricuspid regurgitation were demonstrated on hotter days and seasons.

Cross-Adaptation: Heat and Cold Adaptation to Improve Physiological and Cellular Responses to Hypoxia

To prepare for extremes of heat, cold or low partial pressures of oxygen (O₂), humans can undertake a period of acclimation or acclimatization to induce environment-specific adaptations, e.g. heat acclimation (HA), cold acclimation (CA), or altitude training. While these strategies are effective, they are not always feasible due to logistical impracticalities. Cross-adaptation is a term used to describe the phenomenon whereby alternative environmental interventions, e.g. HA or CA, may be a beneficial alternative to altitude interventions, providing physiological stress and inducing adaptations observable at altitude. HA can attenuate physiological strain at rest and during moderate-intensity exercise at altitude via adaptations allied to improved O₂ delivery to metabolically active tissue, likely following increases in plasma volume and reductions in body temperature. CA appears to improve physiological responses to altitude by attenuating the autonomic response to altitude. While no cross-acclimation-derived exercise performance/capacity data have been measured following CA, post-HA improvements in performance underpinned by aerobic metabolism, and therefore dependent on O₂ delivery at altitude, are likely. At a cellular level, heat shock protein responses to altitude are attenuated by prior HA, suggesting that an attenuation of the cellular stress response and therefore a reduced disruption to homeostasis at altitude has occurred. This process is known as cross-tolerance. The effects of CA on markers of cross-tolerance is an area requiring further investigation. Because much of the evidence relating to cross-adaptation to altitude has examined the benefits at moderate to high altitudes, future research examining responses at lower altitudes should be conducted, given that these environments are more frequently visited by athletes and workers. Mechanistic work to identify the specific physiological and cellular pathways responsible for cross-adaptation between heat and altitude, and between cold and altitude, is warranted, as is exploration of benefits across different populations and physical activity profiles.

Assessment of skin temperature during regional anaesthesia-What the anaesthesiologist should know

Body temperature homeostasis is accurately regulated by complex feedback-driven neuronal mechanisms, which involve a multitude of thermoregulatory pathways. Thus, core temperature is constantly maintained within a narrow range. As one of the most effective regulatory systems skin temperature is dependent on skin blood flow. Skin blood flow in turn is highly dependent on sympathetic activity. Regional anaesthesia leads to blockade not only of somatosensory and motor nerve fibres but also of sympathetic fibres. As a consequence, vasoconstrictor tonic activity is abrogated and a vasodilation leads to an increase in skin blood flow and temperature. The aim of this review was to summarize the general physiology of thermoregulation and skin temperature as well as the alterations during regional anaesthesia. The main focus was the usefulness of measuring skin temperature as an indicator of regional anaesthesia success. According to the available literature, assessment of skin temperature can indeed serve to predict success of regional anaesthesia. Hence, it is important to realize that relevant and reliable temperature increase is only seen in the most distal body parts, ie fingers and toes. More proximally, temperature changes are frequently small and inconsistent, which means that assessment of block levels is not possible by temperature measurement. Furthermore, relevant skin temperature increases will only be observed in patients, which are initially vasoconstricted. In conclusion, measurement of skin temperature represents a reliable and feasible diagnostic tool to assess and predict the success or failure of regional anaesthesia procedures, especially in patients in which sensory testing is impossible.

Temperature-Controllable Hydrogels in Double-Walled Microtube Structure Prepared by Using a Triple Channel Microfluidic System

Hydrogels in the shape of double-walled microtubes possess great potential for development into artificial human blood vessels. In this work, we have prepared temperature-responsive tubular hydrogels with selectively controllable wall diameters, by using alginate templated photopolymerization in a triple channel microfluidic device. These tubular hydrogels mimic human blood vessels because of the separate thermally active inner and passive outer walls. The different behavior of each wall leads to the expansion of the hollow center volume with increasing temperature. This temperature-based control of the hollow center volume cannot be achieved in the case of conventional hydrogel microtubes. Furthermore, through this method, the hydrogels can be modified to achieve a controllable outer diameter while maintaining the hollow center dimensions simply by changing the position of the hydrogel walls. The ability to change the layer properties of the developed system indicates that the preparation of hydrogels with various monomers is possible.

Theoretical analysis of evaporative cooling of classic heat stroke patients

Heat stroke is a serious health concern globally, which is associated with high mortality. Newer treatments must be designed to improve outcomes. The aim of this study is to evaluate the effect of variations in ambient temperature and wind speed on the rate of cooling in a simulated heat stroke subject using the dynamic model of Wissler. We assume that a 60-year-old 70-kg female suffers classic heat stroke after walking fully exposed to the sun for 4 h while the ambient temperature is 40 °C, relative humidity is 20%, and wind speed is 2.5 m/s^-1. Her esophageal and skin temperatures are 41.9 and 40.7 °C at the time of collapse. Cooling is accomplished by misting with lukewarm water while exposed to forced airflow at a temperature of 20 to 40 °C and a velocity of 0.5 or 1 m/s^-1. Skin blood flow is assumed to be either normal, one-half of normal, or twice normal. At wind speed of 0.5 m/s^-1 and normal skin blood flow, the air temperature decreased from 40 to 20 °C, increased cooling, and reduced time required to reach to a desired temperature of 38 °C. This relationship was also maintained in reduced blood flow states. Increasing wind speed to 1 m/s^-1 increased cooling and reduced the time to reach optimal temperature both in normal and reduced skin blood flow states. In conclusion, evaporative cooling methods provide an effective method for cooling classic heat stroke patients. The maximum heat dissipation from the simulated model of Wissler was recorded when the entire body was misted with lukewarm water and applied forced air at 1 m/s at temperature of 20 °C.

Aging and Thermoregulatory Control: The Clinical Implications of Exercising under Heat Stress in Older Individuals

Climate change is predicted to bring about a greater variability in weather patterns with an increase in extreme weather events such as sustained heat waves. This change may have a direct impact on population health since heat waves can exceed the physiological limit of compensability of vulnerable individuals. Indeed, many clinical reports suggest that individuals over the age of 60 years are consistently the most vulnerable, experiencing significantly greater adverse heat-related health outcomes than any other age cohort during environmental heat exposure. There is now evidence that aging is associated with an attenuated physiological ability to dissipate heat and that the risk of heat-related illness in these individuals is elevated, particularly when performing physical activity in the heat. The purpose of this review is to discuss mechanisms of thermoregulatory control and the factors that may increase the risk of heat-related illness in older individuals. An understanding of the mechanisms responsible for impaired thermoregulation in this population is of particular importance, given the current and projected increase in frequency and intensity of heat waves, as well as the promotion of regular exercise as a means of improving health-related quality of life and morbidity and mortality. As such, the clinical implications of this work in this population will be discussed.

Climate change and temperature extremes: A review of heat- and cold-related morbidity and mortality concerns of municipalities

Cold and hot weather are associated with mortality and morbidity. Although the burden of temperature-associated mortality may shift towards high temperatures in the future, cold temperatures may represent a greater current-day problem in temperate cities. Hot and cold temperature vulnerabilities may coincide across several personal and neighborhood characteristics, suggesting opportunities for increasing present and future resilience to extreme temperatures. We present a narrative literature review encompassing the epidemiology of cold- and heat-related mortality and morbidity, related physiologic and environmental mechanisms, and municipal responses to hot and cold weather, illustrated by Detroit, Michigan, USA, a financially burdened city in an economically diverse metropolitan area. The Detroit area experiences sharp increases in mortality and hospitalizations with extreme heat, while cold temperatures are associated with more gradual increases in mortality, with no clear threshold. Interventions such as heating and cooling centers may reduce but not eliminate temperature-associated health problems. Furthermore, direct hemodynamic responses to cold, sudden exertion, poor indoor air quality and respiratory epidemics likely contribute to cold-related mortality. Short- and long-term interventions to enhance energy and housing security and housing quality may reduce temperature-related health problems. Extreme temperatures can increase morbidity and mortality in municipalities like Detroit that experience both extreme heat and prolonged cold seasons amidst large socioeconomic disparities. The similarities in physiologic and built-environment vulnerabilities to both hot and cold weather suggest prioritization of strategies that address both present-day cold and near-future heat concerns.

Differential contribution of calcium channels to α1-adrenoceptor-mediated contraction is responsible for diverse responses to cooling between rat tail and iliac arteries

Our previous studies have shown that α₁-adrenoceptors, in addition to α₂-adrenoceptors, are involved in enhanced contraction of cutaneous blood vessels during cooling. The present study aimed to elucidate the mechanism underlying it. In tail and iliac arteries isolated from rats, isometric contraction was measured using a myograph and the phosphorylation level of myosin phosphatase target subunit 1 (MYPT1) was quantified by western blotting. The phenylephrine-induced contraction was enhanced by cooling to 24 °C in tail arteries, but was suppressed in iliac arteries. Endothelium denudation or treatment with iberiotoxin enhanced the phenylephrine-induced contraction in tail arteries at 37 °C; however, neither affected the contraction at 24 °C. The phenylephrine-induced contraction at 37 °C was largely suppressed by nifedipine in iliac arteries, but only slightly in tail arteries. The Rho kinase inhibitor H-1152 largely suppressed the phenylephrine-induced contraction at 24 °C, but only slightly at 37 °C, in both arteries. The phosphorylation level of MYPT1 at Thr855 in tail arteries was increased by the cooling. Taken together, these results suggest the following mechanism in regard to cooling-induced enhancement of α₁-adrenoceptor-mediated contraction in tail arteries: Cooling enhances the contraction of tail arteries via α₁-adrenoceptor stimulation by reducing endothelium-dependent, large-conductance Ca²⁺-activated K⁺ channel-mediated relaxation and by inducing Rho kinase-mediated Ca²⁺ sensitization, although the latter occurs even in iliac arteries. A smaller contribution of voltage-dependent Ca²⁺ channels, which are largely suppressed by cooling, to α₁-adrenoceptor-mediated contraction in tail arteries seems to be more crucially involved in the appearance of the enhanced contractile response to cooling.

Infrared thermal imaging: Positive and negative emotions modify the skin temperatures of monkey and ape faces

Facial thermography has enabled researchers to noninvasively and continuously measure the changes of a range of emotional states in humans. The present work used this novel technology to study the effect of positive and negative emotions in nonhuman primates by focusing on four facial areas (the peri-orbital area, the nose bridge, the nose tip, and the upper lip). Monkeys and apes were examined for positive emotions (during interactions with toys and during tickling) and for negative emotions (during food delay and teasing). For the combined toy and tickling condition, the results indicated a drop in the nose tip temperature and a tendency of an increase in the peri-orbital temperature. For the combined food delay and teasing condition, the results also revealed a rise in the upper lip temperature of the subjects. These different effects on the facial temperatures in monkeys and apes most likely reflect distinctive physiological reactions of a primordial primate emotion system. We conclude that facial thermal imaging represents a promising physiologically grounded technology to noninvasively and continuously obtain reliable data on emotional states in nonhuman primates, which may help modernize research on emotions in nonhuman primates and enhance our understanding of the evolution of human emotions.

Measurement of peripheral blood flow in patients with peripheral artery disease: Methods and considerations

Peripheral artery disease (PAD) is a manifestation of generalized atherosclerosis which results in hemodynamic compromise of oxygen and substrate delivery to the lower extremity skeletal muscles. Hemodynamic assessments are vital in PAD diagnosis and in the evaluation of strategies aimed at treating claudication (i.e. exercise training, revascularization, and pharmacological agents). Venous occlusion plethysmography (VOP) is a century-old, non-invasive technique used to quantify limb blood flow and has been used to evaluate hemodynamic compromise in patients with PAD. However, the literature suggests a wide array of methodological variability in the measurement and analysis of limb blood flow using VOP. In this manuscript, we overview the clinical application of VOP measurement, and secondly we review the methodological variation that occurs during the measurement and analysis of VOP in healthy individuals and in patients with claudication.

Cardiovascular diseases, cold exposure and exercise

Both acute and prolonged cold exposure affect cardiovascular responses, which may be modified by an underlying cardiovascular disease. In addition, exercise in a cold environment increases cardiovascular strain further, but its effects among persons with cardiovascular diseases are not well known. Controlled studies employing whole-body or local cold exposure demonstrate comparable or augmented increase in cardiac workload, but aggravated cutaneous vasoconstriction in persons with mild hypertension. A strong sympathetic stimulation of a cold pressor test, increases cardiac workload in persons with coronary artery disease (CAD), but does not markedly differ from those with less severe disease or healthy. However, cold exposure reduces myocardial oxygen supply in CAD, which may lead to ischemia. Exercise in cold often augments cardiac workload in persons with CAD more than when performed in thermoneutral conditions. At the same time, reduced myocardial perfusion may lead to earlier ischemia, angina and impaired performance. Also having a heart failure deteriorates submaximal and maximal performance in the cold. Antianginal medication is beneficial in the cold in lowering blood pressure, but does not affect the magnitude of cold-related cardiovascular responses in hypertension. Similarly, the use of blood pressure lowering medication improves exercise performance in cold both among persons with CAD and heart failure. Both the acute and seasonal effects of cold and added with exercise may contribute to the higher morbidity and mortality of those with cardiovascular diseases. Yet, more controlled studies for understanding the pathophysiological mechanisms behind the adverse cold-related health effects are warranted.

The cold effect of ambient temperature on ischemic and hemorrhagic stroke hospital admissions: A large database study in Beijing, China between years 2013 and 2014-Utilizing a distributed lag non-linear analysis

The effects of ambient temperature on stroke death in China have been well addressed. However, few studies are focused on the attributable burden for the incident of different types of stroke due to ambient temperature, especially in Beijing, China. We purpose to assess the influence of ambient temperature on hospital stroke admissions in Beijing, China. Data on daily temperature, air pollution, and relative humidity measurements and stroke admissions in Beijing were obtained between 2013 and 2014. Distributed lag non-linear model was employed to determine the association between daily ambient temperature and stroke admissions. Relative risk (RR) with 95% confidence interval (CI) and Attribution fraction (AF) with 95% CI were calculated based on stroke subtype, gender and age group. A total number of 147, 624 stroke admitted cases (including hemorrhagic and ischemic types of stroke) were documented. A non-linear acute effect of cold temperature on ischemic and hemorrhagic stroke hospital admissions was evaluated. Compared with the 25th percentile of temperature (1.2 °C), the cumulative RR of extreme cold temperature (first percentile of temperature, -9.6 °C) was 1.51 (95% CI: 1.08-2.10) over lag 0-14 days for ischemic type and 1.28 (95% CI: 1.03-1.59) for hemorrhagic stroke over lag 0-3 days. Overall, 1.57% (95% CI: 0.06%-2.88%) of ischemic stroke and 1.90% (95% CI: 0.40%-3.41%) of hemorrhagic stroke was attributed to the extreme cold temperature over lag 0-7 days and lag 0-3 days, respectively. The cold temperature's impact on stroke admissions was found to be more obvious in male gender and the youth compared to female gender and the elderly. Exposure to extreme cold temperature is associated with increasing both ischemic and hemorrhagic stroke admissions in Beijing, China.

Skin vasoconstriction as a heat conservation thermoeffector

Cold exposure stimulates heat production and conservation to protect internal temperature. Heat conservation is brought about via reductions in skin blood flow. The focus, here, is an exploration of the mechanisms, particularly in humans, leading to that cutaneous vasoconstriction. Local skin cooling has several effects: (1) reduction of tonic nitric oxide formation by inhibiting nitric oxide synthase and element(s) downstream of the enzyme, which removes tonic vasodilator effects, yielding a relative vasoconstriction; (2) translocation of intracellular alpha-2c adrenoceptors to the vascular smooth-muscle cell membrane, enhancing adrenergic vasoconstriction; (3) increased norepinephrine release from vasoconstrictor nerves; and (4) cold-induced vasodilation, seen more clearly in anastomoses-rich glabrous skin. Cold-induced vasodilation occurs in nonglabrous skin when nitric oxide synthase or sympathetic function is blocked. Reflex responses to general body cooling complement these local effects. Sympathetic excitation leads to the increased release of norepinephrine and its cotransmitter neuropeptide Y, each of which contributes significantly to the vasoconstriction. The contributions of these two transmitters vary with aging, disease and, in women, reproductive hormone status. Interaction between local and reflex mechanisms is in part through effects on baseline and in part through removal of the inhibitory effects of nitric oxide on adrenergic vasoconstriction.

Thermodysregulation in persons with spinal cord injury: case series on use of the autonomic standards

INTRODUCTION

The ability to maintain core body temperature (Tcore) within a narrow range (37 ± 0.6 °C), despite exposure to a wide range of ambient temperatures, is essential in order to provide an optimal environment for vital organs, the central nervous system (CNS), and cellular processes to function. High-level (above T6) spinal cord injury (SCI) interrupts the autonomic nervous system's ability to carry out hypothalamic regulation of thermoregulatory mechanisms for both heat dissipation and conservation. This interruption leaves persons with high-level SCI vulnerable to hyper and hypothermia even during exposure to relatively mild ambient temperatures. The goal of the Autonomic Standards is to enable the clinician to quickly identify those individuals with SCI who may be most at risk for thermoregulatory dysfunction.

CASE PRESENTATION

Case 1: Heat Exhaustion, Case 2: Heat Stroke in absence of CNS symptoms, Case 3: Heat Exhaustion.

DISCUSSION

The three cases demonstrate the signs and symptoms that may accompany hyperthermia in persons with SCI. The onset may be quite rapid and the condition persistent, despite ambient temperatures being much less intense than expected to be necessary to induce similar conditions in able-bodied (AB) persons. The responses of the persons in the case studies to the temperature regulation and autonomic control of sweating sections of the Autonomic Standards would identify them as being vulnerable and warrant providing appropriate exposure guidelines and precautions to them and their caregivers.

Comparison of the effects of 1MHz and 3MHz therapeutic ultrasound on endothelium-dependent vasodilation of humans: a randomised clinical trial

OBJECTIVE

To compare the effects of different waveforms of 1MHz and 3MHz therapeutic ultrasound on endothelial function in healthy subjects.

DESIGN

Randomised placebo-controlled, crossover study with concealed allocation and assessor blinding.

SETTING

Imaging Centre of the University Hospital.

PARTICIPANTS

Thirty volunteers aged between 18 and 35 years were divided into two homogeneous groups (1MHz and 3MHz).

INTERVENTIONS

Continuous (CUT; 0.4W/cm^2SATA), pulsed (PUT; 20% duty cycle, 0.08W/cm^2SATA) and placebo waveforms (equipment off) of ultrasound (1MHz and 3MHz) were randomized and applied over the brachial artery for 5minutes.

MAIN OUTCOME MEASURES

Endothelial function was evaluated using the flow-mediated dilation (FMD) technique.

RESULTS

Both 1MHz [CUT: mean difference 4%, 95% confidence interval (CI) 2 to 6%, P<0.001; PUT: mean difference 4%, 95% CI 2 to 6%, P<0.001] and 3MHz (CUT: mean difference 4%, 95% CI 2 to 6%, P<0.001; PUT: mean difference 4%, 95% CI 2 to 6%, P<0.001) of therapeutic ultrasound increased %FMD by approximately 4% compared with the placebo waveforms. The endothelium-dependent vasodilator responses were the same for both types of waves and frequencies. No differences in baseline diameter, hyperaemic flow, and nitroglycerin-mediated diameter and vasodilation were observed between groups.

CONCLUSION

Both CUT and PUT ultrasound waveforms improved endothelial function. The 1MHz and 3MHz frequencies of therapeutic ultrasound led to similar improvement in endothelial function in healthy volunteers. Clinical trial registration number RBR-4z5z3t.

Working Memory Impairments in Chromosome 22q11.2 Deletion Syndrome: The Roles of Anxiety and Stress Physiology

Stress and anxiety have a negative impact on working memory systems by competing for executive resources and attention. Broad memory deficits, anxiety, and elevated stress have been reported in individuals with chromosome 22q11.2 deletion syndrome (22q11.2DS). We investigated anxiety and physiological stress reactivity in relation to visuospatial working memory impairments in 20 children with 22q11.2DS and 32 typically developing (TD) children ages 7 to 16. Children with 22q11.2DS demonstrated poorer working memory, reduced post-stress respiratory sinus arrhythmia recovery, and overall increased levels of cortisol in comparison to TD children. Anxiety, but not physiological stress responsivity, mediated the relationship between 22q11.2DS diagnosis and visuospatial working memory impairment. Findings indicate that anxiety exacerbates impaired working memory in children with 22q11.2DS.

Cold-Blooded Attention: Finger Temperature Predicts Attentional Performance

Thermal stress has been shown to increase the chances of unsafe behavior during industrial and driving performances due to reductions in mental and attentional resources. Nonetheless, establishing appropriate safety standards regarding environmental temperature has been a major problem, as modulations are also be affected by the task type, complexity, workload, duration, and previous experience with the task. To bypass this attentional and thermoregulatory problem, we focused on the body rather than environmental temperature. Specifically, we measured tympanic, forehead, finger and environmental temperatures accompanied by a battery of attentional tasks. We considered a 10 min baseline period wherein subjects were instructed to sit and relax, followed by three attentional tasks: a continuous performance task (CPT), a flanker task (FT) and a counting task (CT). Using multiple linear regression models, we evaluated which variable(s) were the best predictors of performance. The results showed a decrement in finger temperature due to instruction and task engagement that was absent when the subject was instructed to relax. No changes were observed in tympanic or forehead temperatures, while the environmental temperature remained almost constant for each subject. Specifically, the magnitude of the change in finger temperature was the best predictor of performance in all three attentional tasks. The results presented here suggest that finger temperature can be used as a predictor of alertness, as it predicted performance in attentional tasks better than environmental temperature. These findings strongly support that peripheral temperature can be used as a tool to prevent unsafe behaviors and accidents.

The Significance of Epidermal Lipid Metabolism in Whole-Body Physiology

The skin is the largest sensory organ of the human body. The skin not only prevents loss of water and other components of the body, but also is involved in regulation of body temperature and serves as an essential barrier, protecting mammals from both routine and extreme environments. Given the importance of the skin in temperature regulation, it is surprising that adaptive alterations in skin functions and morphology only vaguely have been associated with systemic physiological responses. Despite that impaired lipid metabolism in the skin often impairs the epidermal permeability barrier and insulation properties of the skin, its role in regulating systemic physiology and metabolism is yet to be recognized.

Effect of Heat Exposure on Cognition in Persons with Tetraplegia

Individuals with cervical spinal cord injury (SCI) have impaired thermoregulatory mechanisms attributed to interruption of motor, sensory, and autonomic neuropathways. To determine the effects of heat exposure on core body temperature (Tcore) and cognitive performance in persons with tetraplegia, 8 individuals with chronic tetraplegia (C3-C7, American Spinal Cord Injury Association Impairment Scale A-B) and 9 able-bodied controls were acclimated to 27°C at baseline (BL) before being exposed to 35°C for up to 120 min (Heat Challenge). Rectal temperature (Tcore), distal skin temperatures (Tsk_avg), sweat rate (QS_avg), microvascular skin perfusion (LDF_avg), and plasma norepinephrine (NE) were measured. Cognitive performance was assessed using Stroop Color and Word and Wechsler Adult Intelligence Scale-Fourth Edition Digit Span tests at BL and at the end of Heat Challenge. After Heat Challenge, Tcore increased 0.78 ± 0.18°C (p < 0.001) in tetraplegics after an average of 118 ± 5 min. Tcore did not change in controls after 120 min. The increase in QS_avg was larger in controls than in tetraplegics (946 ± 672% vs. 51 ± 12%; p = 0.007, respectively). LDF_avg increased only in controls (109 ± 93%; p = 0.008). Tsk_avg appeared to increase less in tetraplegics than in controls. Plasma NE levels remained lower in tetraplegics compared to controls after Heat Challenge (86 ± 64 vs. 297 ± 84 pg/mL, respectively; p < 0.001). Stroop Color, Interference, and WAIS-IV Sequence scores increased only in tetraplegics (19.4 ± 17.2%; p < 0.05, 8.3 ± 5.9%; p < 0.05, 29.1 ± 27.4%; p < 0.05, respectively). Dysfunctional thermoregulatory mechanisms in the tetraplegic group allowed Tcore to rise from subnormal levels to normothermia during heat exposure. Normothermia was associated with improvements in attention, working memory, and executive function.

Long-term management of distinct facial flushing and persistent erythema of rosacea by treatment with carvedilol

BACKGROUND

The treatment of persistent erythema and flushing episodes in patients with rosacea remains a clinical challenge. A possible therapeutic option could be the use of antihypertensive drugs.

OBJECTIVES

We therefore evaluated the effect of the non-selective β-blocker carvedilol in five Caucasian patients.

METHODS

In a monocentric retrospective case study, the patients were treated with carvedilol titrated up to 12.5 mg twice a day over at least six months. Patients self assessment (PSA), clinicians erythema assessment (CEA), and the patients levels of embarrassment and satisfaction were performed by questionaires.

RESULTS

The CEA grade description as well as the PSA grade description decreased remarkably in all five patients. Furthermore, all patients reported to have a major improvement of their level of satisfaction and no feelings of embarrassment anymore.

CONCLUSIONS

These findings demonstrate that facial flushing and persistent erythema can be effectively treated by carvedilol long-term with a fast onset of improvement in a dose well tolerated.

Divergent temperaments are associated with beef tenderness and the inhibitory activity of calpastatin

Ninety-six feedlot-finished Nellore steers were used to verify the relationship between temperament indicators and meat tenderization. Temperament index (TI), chute score (CS), and average of exit velocity (EV) with CS (AT) presented low positive correlations (P≤0.05) with shear force, either at 2 or 16days postmortem (WBSF-16). The rectal temperature was consistently correlated with temperament indicators (TI, CS, and AT) and WBSF-16. Two groups (n=12) representing the most tender (39.2±4.9N) and most tough meat (94.1±11.8N), based on WBSF-16, were compared for temperament, and calpastatin activity (CASTa) was determined 48h postmortem. The tender group presented lower EV, TI, and AT (P≤0.05). The tender group exhibited lower (P≤0.05) CASTa in the triceps brachii muscle, but there was no difference in CASTa in the longissimus lumborum muscle between WBSF groups. Meat tenderness and inhibitory activity of calpastatin may be associated with divergent temperament indices in zebu cattle.

Postsynaptic α1-Adrenergic Vasoconstriction Is Impaired in Young Patients With Vasovagal Syncope and Is Corrected by Nitric Oxide Synthase Inhibition

BACKGROUND

Syncope is a sudden transient loss of consciousness and postural tone with spontaneous recovery; the most common form is vasovagal syncope (VVS). During VVS, gravitational pooling excessively reduces central blood volume and cardiac output. In VVS, as in hemorrhage, impaired adrenergic vasoconstriction and venoconstriction result in hypotension. We hypothesized that impaired adrenergic responsiveness because of excess nitric oxide can be reversed by reducing nitric oxide.

METHODS AND RESULTS

We recorded cardiopulmonary dynamics in supine syncope patients and healthy volunteers (aged 15-27 years) challenged with a dose-response using the α1-agonist phenylephrine (PE), with and without the nitric oxide synthase inhibitor N(G)-monomethyl-L-arginine, monoacetate salt (L-NMMA). Systolic and diastolic pressures among control and VVS were the same, although they increased after L-NMMA and saline+PE (volume and pressor control for L-NMMA). Heart rate was significantly reduced by L-NMMA (P<0.05) for control and VVS compared with baseline, but there was no significant difference in heart rate between L-NMMA and saline+PE. Cardiac output and splanchnic blood flow were reduced by L-NMMA for control and VVS (P<0.05) compared with baseline, while total peripheral resistance increased (P<0.05). PE dose-response for splanchnic flow and resistance were blunted for VVS compared with control after saline+PE, but enhanced after L-NMMA (P<0.001). Postsynaptic α1-adrenergic vasoconstrictive impairment was greatest in the splanchnic vasculature, and splanchnic blood flow was unaffected by PE. Forearm and calf α1-adrenergic vasoconstriction were unimpaired in VVS and unaffected by L-NMMA.

CONCLUSIONS

Impaired postsynaptic α1-adrenergic vasoconstriction in young adults with VVS can be corrected by nitric oxide synthase inhibition, demonstrated with our use of L-NMMA.

Systemic and Local Effects of Warm Oxygen Exposure to the Lower Extremities in Healthy Volunteers

INTRODUCTION

Warmth to the extremity is known to improve the cutaneous blood flow and tissue perfusion. Oxygen is essential for healing of chronic wounds. Topical oxygen therapy has become standard therapy in management of lower extremity wounds. A combination of local heat and oxygen is likely to be beneficial in many clinical scenarios of non-healing wounds without any systemic effects.

AIM

To evaluate the local and systemic effects of the exposure of extremity to warm oxygen in healthy volunteers.

MATERIALS AND METHODS

Thirty one volunteers were included in the study. The index foot was exposed to oxygen 7l/min, 93%-95% concentration at temperature of 43^oC for 90 minutes with the device. The following parameters such as basal and periprocedural blood pressure, body temperature, heart rate, 24 lead ECG, temperatures at foot and plethysmographic waveforms from the index foot were measured. A NRS-11 questionnaire was asked to the patient to rate his or her pain from 0 to 10 and documented by health care worker at the end of the session.

RESULTS

The skin temperature of index foot reached to 34^oC from 32.9^oC, (p=0.011). The average pulse amplitude changed from 39.8 mV to 79.8 mV over the duration of the experiment (p< 0.001). Overall heart rate and core body temperature decreased and not much change in blood pressure.

CONCLUSION

The result of the study can be extrapolated to the healing of chronic non healing wounds using warm oxygen therapy. Further studies are required on patient population to prove benefits in clinical settings.

Response of women using oral contraception to exercise in the heat

PURPOSE

To compare the response of long-term oral contraceptive users (WomenOC; n = 8) to naturally menstruating women (WomenNM; n = 8) at rest and during exercise in temperate (TEMP; 22 °C) and hot (HEAT; 35 °C) conditions.

METHODS

Participants performed a three-stage cycling trial in each condition at 90, 135, and 180% of lactate threshold 1 (total = 52.5 min). Heart rate (HR) and core temperature (T _c) were recorded continuously, whereas blood pressure (BP), ratings of perceived exertion (RPE), blood lactate [La^-], and skin blood flow (BF_sk) were recorded every 7.5 min.

RESULTS

Baseline T _c was higher in WomenOC (37.5 ± 0.2, 37.6 ± 0.3 °C) than WomenNM (37.2 ± 0.2, 37.0 ± 0.4 °C) before the TEMP (p = 0.03) and HEAT (p < 0.01) trials, respectively. This difference remained for 22.5 min into both trials (p ≤ 0.05), after which time no between-group differences were found (p > 0.05). BF_sk measured in WomenNM plateaued from 7.5 min in the HEAT, whereas BF_sk measured in WomenOC increased for 15.0 min (p = 0.02) before plateauing. There were no between-group differences in HR, BP, or blood [La^-] before or throughout either trial (p > 0.05). WomenOC had higher (p ≤ 0.04) RPE values than WomenNM in the HEAT, reporting 8 ± 1 and 6 ± 2 at the end of Stage 3, respectively.

CONCLUSIONS

WomenOC concluded both trials with a comparable T _c to WomenNM, but had a prolonged BF_sk response and elevated RPE in the HEAT. Changes to BF_sk and RPE observed in women using OC may have implications for exercise tolerance in hot conditions.

Novel contactless approach for assessment of venous occlusion plethysmography by video recordings at the green illumination

Occlusion plethysmography is an important method for assessment of the status of the cardiovascular system, which provides valuable information concerning arterial and venous blood flow, including mechanisms of their regulation. All up-to-date systems estimate change of the limb's volume during occlusion by contact-type sensors. The objective of the research is demonstration of feasibility of the novel approach to measuring the blood flow during venous occlusion by using imaging photoplethysmography (PPG). Twenty healthy individuals participated in the experiment. We used four synchronized video cameras to record all-around view of the forearm illuminated by the green light. After the recording, the PPG waveform was calculated in more than 4000 non-overlapping Regions of Interest (ROI). In the most of the ROIs, the waveform shape was typical for classical plethysmography with the distinctive linear growth of the signal. Speed of the signal change was the same along the forearm but it varied along the forearm's circumference. These findings allows us to hypothesize that the PPG waveform is the direct consequence of the forearm blood flow. Therefore, the novel technique could be applied to the same medical examinations as the classical plethysmography, but it is more advantageous because of non-contact nature and easiness in implementation.