Increase In Skin Blood Flow Research Articles

Hyperthermia and Exertional Heatstroke During Running, Cycling, Open Water Swimming, and Triathlon Events.

Few previous epidemiological studies, sports medicine position statements, and expert panel consensus reports have evaluated the similarities and differences of hyperthermia and exertional heatstroke (EHS) during endurance running, cycling, open water swimming, and triathlon competitions. Accordingly, we conducted manual online searches of the PubMed and Google Scholar databases using pre-defined inclusion criteria. The initial manual screenings of 1192 article titles and abstracts, and subsequent reviews of full-length pdf versions identified 80 articles that were acceptable for inclusion. These articles indicated that event medical teams recognized hyperthermia and EHS in the majority of running and triathlon field studies (range, 58.8 to 85.7%), whereas few reports of hyperthermia and EHS appeared in cycling and open water swimming field studies (range, 0 to 20%). Sports medicine position statements and consensus reports also exhibited these event-specific differences. Thus, we proposed mechanisms that involved physiological effector responses (sweating, increased skin blood flow) and biophysical heat transfer to the environment (evaporation, convection, radiation, and conduction). We anticipate that the above information will help race directors to distribute pre-race safety advice to athletes and will assist medical directors to better allocate medical resources (eg, staff number and skill sets, medical equipment) and optimize the management of hyperthermia and EHS.

Observations of cold-induced vasodilation in persons with spinal cord injuries.

Acute experimental study. Cold-induced vasodilation is a local mechanism of protection against frostbite in non-injured persons. We assessed whether an increase in skin blood flow (SkBF) during local cooling (LC) was observed in individuals with spinal cord injuries (SCIs) and if the response patterns differed between region levels or sites. Laboratory of Wakayama Medical University and the affiliated clinics, Japan. A local cooler device (diameter 4 cm) was placed on the chest (sensate) and right thigh (non-sensate) in persons with cervical (SCIC; n = 9) and thoracolumbar SCIs (SCITL; n = 9). After the surface temperature under the device was controlled at 33 °C for 10 min (baseline), LC (-0.045 °C/s) was applied and the skin temperature was maintained at 15 and 8 °C for 15 min of each stage. SkBF (laser Doppler flowmetry) was monitored using a 1-mm needle-type probe inserted into its center. The percent change in SkBF (%ΔSkBF) on the chest remained unchanged until the end of 15 °C stage; thereafter, it increased to a level at least 70% greater than the baseline during the 8 °C stage in both groups. The %ΔSkBF on the thigh in both SCIC and SCITL notably increased from 8 and 6 min respectively, during the 8°C stage, compared to 1 min before the stage; however, it did not exceed the baseline level. An increase in SkBF during LC was observed both in the sensate and non-sensate areas in SCIs, although the magnitude was larger in the sensate area.

(366) Potential Effectiveness of Focused Vibration Treatment for Psychogenic Erectile Dysfunction: A Case Series

Abstract Introduction The current non-pharmacological treatment of psychogenic erectile dysfunction (pED) is based on cognitive-behavioral interventions that often involve the participation of the partner, such as desensitization procedures, sensory focusing, and couples counseling. However, it is important to note that in many cases, patients may not have a stable partner or their partner cannot participate in the treatment. The application of local mechanical vibration has shown promising results in increasing skin blood flow and nitric oxide production in healthy young adults. The relaxation of smooth muscle in the penis initiates and maintains an erection. The local release of nitric oxide from autonomic dilator nerves and vascular endothelium is crucial in initiating and sustaining this process. Technological advances have allowed the design of vibrating devices that men can use during sexual encounters. Objective To determine if the on-demand use of a focused vibration device can increase blood flow and promote relaxation of erectile tissue to improve erectile function in patients with pED. Methods Seven sexually active men diagnosed with pED based on criteria for Erectile Disorder from the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) and without a stable partner, were instructed to use a vibrating device called TENUTO II during their sexual encounters for duration of 8 weeks. This device generates focal vibrations on the penis and the perineal area in intervals of 10 seconds of vibration followed by 10 seconds of pause, with a frequency of 50Hz and an amplitude of 2mm. The five-item Spanish version of the International Index of Erectile Function (IIEF-5) questionnaire was used to assess symptoms before and after the procedure and the Erectile Dysfunction Inventory of Treatment Satisfaction (EDITS) questionnaire was used for evaluating satisfaction with treatment. Results After the using the device, all patients enrolled with a mean age of 36.1 years (range 28-45) experienced an improvement in erectile function, mean IIEF-5 score pretreatment was 11(range 5–13) mean posttreatment IIEF score was 20 (range 18-27). No adverse effects were reported during the treatment. Conclusions This case series suggests that use of an on-demand focused vibration device could be a potentially effective and safe therapeutic option for men with pED. However, further studies with a larger number of participants and a more rigorous research design are needed to confirm these preliminary findings. Disclosure Yes, this is sponsored by industry/sponsor: MysteryVibe. Clarification: Industry funding only - investigator initiated and executed study. Any of the authors act as a consultant, employee or shareholder of an industry for: Mysteryvibe.

Effects of alternating pressure patterns on sacral skin blood flow responses in people with spinal cord injury.

Alternating pressure support surface (APSS) is a common support surface for treating pressure injury in individuals with spinal cord injury (SCI). However, conflicting results on the effectiveness of APSS have been reported and may be associated with inappropriate configurations of APSS. The objectives of this study were to compare the different pressure amplitudes (75/5 mmHg [alternating between 75 and 5 mmHg] vs. 65/15 mmHg) and cycle periods (5 min [4 cycles] vs. 2.5 min [8 cycles]) of alternating pressure on sacral skin blood flow responses in 10 individuals with SCI. Sacral skin blood flow during and after loading of four alternating pressure protocols was assessed using laser Doppler flowmetry and was normalised to the value before loading (10-min baseline, 20-min loading and 10-min recovery). The results demonstrated that during the high-pressure phase, there was a significant difference between the 75/5 and 65/15 mmHg protocols (0.3658 ± 0.0688 for 75/5 mmHg and 0.1702 ± 0.0389 for 65/15 mmHg, p < 0.05); and during the low-pressure phase, there was a significant difference between the 75/5 and 65/15 mmHg protocols (1.7184 ± 0.262 for 75/5 mmHg and 0.5916 ± 0.1378 for 65/15 mmHg, p < 0.05). There were no differences between cycle periods in skin blood flow responses. No adverse events were reported. Our finding indicates that the pressure amplitude of alternating pressure is a significant factor affecting sacral skin blood flow responses. An appropriate configuration of alternating pressure is needed to effectively increase skin blood flow and tissue viability in individuals with SCI.

Impact of Topical Capsaicin Cream on Thermoregulation and Perception While Walking in the Cold.

Capsaicin, a chili pepper extract, can stimulate increased skin blood flow (SkBF) with a perceived warming sensation on application areas. Larger surface area application may exert a more systemic thermoregulatory response. Capsaicin could assist with maintaining heat transport to the distal extremities, minimizing cold weather injury risk. However, the thermoregulatory and perceptual impact of topical capsaicin cream application prior to exercise in the cold is unknown. Following application of either a 0.1% capsaicin or control cream to the upper and lower extremities (10 g total, ∼40-50% body surface area), 11 participants in shorts and a t-shirt were exposed to 30 min of cold (0 °C, 40% relative humidity). Exposures comprised of 5 min seated rest, 20 min walking (1.6 m·s-1, 5% grade), and 5 min seated rest. Temperature (skin, core), SkBF, skin conductivity, heart rate, thermal sensation, and thermal comfort were measured throughout. The capsaicin treatment did not differ from the control treatment in skin temperature (treatment mean: 30.0 ± 2.5, 30.1 ± 2.4 °C, respectively, p = 0.655), core temperature (treatment mean: 37.3 ± 0.5, 37.4 ± 0.4 °C, respectively, p = 0.113), SkBF (treatment mean: -8.4 ± 10.0, -11.1 ± 10.7 A.U., respectively, p = 0.492), skin conductivity (treatment mean: -0.7 ± 5.1, 0.4 ± 6.4 µS, respectively, p = 0.651), or heart rate (treatment mean: 83 ± 29, 85 ± 28 beats·minute-1, respectively, p = 0.234). The capsaicin and control treatments also did not differ in thermal sensation (p = 0.521) and thermal comfort (p = 0.982), with perceptual outcomes corresponding with feeling "cool" and "just uncomfortable," respectively. 0.1% topical capsaicin application to exposed limbs prior to walking in a cold environment does not alter whole-body thermoregulation or thermal perception.

Comparing thermoregulatory responses between short and long moderate intensity intermittent exercise protocols with the same duty cycle

To date, the thermoregulatory response between continuous and intermittent exercises has been investigated whilst limited studies are available to examine the thermoregulatory responses between different modes of intermittent exercises. We sought to determine the effect of two patterns of short duration intermittent exercises (180:180 (3-min) and 30:30 s (30-s) work: rest) on thermoregulatory responses in a temperate environment (25 °C, 50% RH, vapor pressure: 1.6 kPa) with low airflow (0.2 m/s). Twelve male participants (Age:24.0(5.0) year; VO2max: 53(8) mL.kg−1.min−1; BSA:1.7(0.1) m2) cycled at 50% VO2max for 60 min in 3-min and 30-s intervals to result in the same 30-min net exercise duration. Core and skin temperatures, the percent increase of skin blood flow (forearm and chest) from baseline and local sweat rate (forearm and chest) were not different between 3-min and 30-s (all P > 0.35) from the onset of exercise to the end of the exercise. Similarly, the mean body temperature onsets of skin blood flow (forearm and chest) and local sweat rates (forearm and chest) were not different between different mode of intermittent exercises (all P > 0.1). Furthermore, thermal sensitivities of skin blood flow (forearm and chest) and local sweat rate (forearm and chest) with increasing mean body temperature were not different between different mode of intermittent exercises (all P > 0.1). We conclude that intermittent exercises with different work periods at moderate exercise intensity did not alter core temperature and thermoeffector responses in a temperate environment. (241/250)

Transfusion increased skin blood flow when initially low in volume-resuscitated patients without acute bleeding.

Alterations in skin blood flow is a marker of inadequate tissue perfusion in critically ill patients after initial resuscitation. The effects of red blood cell transfusions (RBCT) on skin perfusion are not described in this setting. We evaluated the effects of red blood cell transfusions on skin tissue perfusion in critically ill patients without acute bleeding after initial resuscitation. A prospective observational study included 175 non-bleeding adult patients after fluid resuscitation requiring red blood cell transfusions. Using laser Doppler, we measured finger skin blood flow (SBF) at skin basal temperature (SBFBT), together with mean arterial pressure (MAP), heart rate (HR), hemoglobin (Hb), central venous pressure (CVP), lactate, and central or mixed venous oxygen saturation before and 1 h after RBCT. SBF responders were those with a 20% increase in SBFBT after RBCT. Overall, SBFBT did not significantly change after RBCT [from 79.8 (4.3-479.4) to 83.4 (4.9-561.6); p = 0.67]. A relative increase equal to or more than 20% in SBFBT after RBCT (SBF responders) was observed in 77/175 of RBCT (44%). SBF responders had significantly lower SBFBT [41.3 (4.3-279.3) vs. 136.3 (6.5-479.4) perfusion units; p < 0.01], mixed or central venous oxygen saturation (62.5 ± 9.2 vs. 67.3% ± 12.0%; p < 0.01) and CVP (8.3 ± 5.1 vs. 10.3 ± 5.6 mmHg; p = 0.03) at baseline than non-responders. SBFBT increased in responders [from 41.3 (4.3-279.3) to 93.1 (9.8-561.6) perfusion units; p < 0.01], and decreased in the non-responders [from 136.3 (6.5-479.4) to 80.0 (4.9-540.8) perfusion units; p < 0.01] after RBCT. Pre-transfusion SBFBT was independently associated with a 20% increase in SBFBT after RBCT. Baseline SBFBT had an area under receiver operator characteristic of 0.73 (95% CI, 0.68-0.83) to predict SBFBT increase; A SBFBT of 73.0 perfusion units (PU) had a sensitivity of 71.4% and a specificity of 70.4% to predict SBFBT increase after RBCT. No significant differences in SBFBT were observed after RBCT in different subgroup analyses. The skin blood flow is globally unaltered by red blood cell transfusions in non-bleeding critically ill patients after initial resuscitation. However, a lower SBFBT at baseline was associated with a relative increase in skin tissue perfusion after RBCT.

Effects of Catecholamines on Blood Flow in Preterm Infants: A Subanalysis of PICC-MBF Trial

Introduction: This study evaluated the correlation between skin blood flow and systemic blood flow and whether skin blood flow can determine the circulatory effects of dopamine and dobutamine on blood flow in very low birth weight (VLBW) infants. Methods: This study was a subanalysis of the PICC-MBF randomized controlled trial. The correlation between skin blood flow and echocardiographic findings was examined. Changes in skin blood flow and blood pressure before and after initiation or dose increase of dopamine and dobutamine were also evaluated. Results: Two hundred and thirty-four participants underwent echocardiography. Skin blood flow was significantly correlated with supra vena cava (SVC) flow (r = 0.31, p < 0.001). Receiver operator characteristic analysis revealed that skin blood flow <17 mL/min effectively detected SVC flow <41 mL/min (area under the curve = 0.83, p < 0.001). Dobutamine significantly increased skin blood flow after initiation or dose increase (p = 0.033) without increasing blood pressure. However, dopamine significantly increased both skin blood flow (p = 0.010) and blood pressure (p < 0.001). Conclusions: Our findings indicated that skin blood flow could be used as a surrogate marker of systemic blood flow in VLBW infants and revealed differences in the effects of dopamine and dobutamine on circulation.

The effect of heat on lung diffusing capacity for carbon monoxide (DLCO) during cycling exercise.

This study aimed to quantify the combined effects of heat exposure and exercise of increasing intensity on pulmonary blood flow using lung diffusing capacity for carbon monoxide (DLCO) as an indirect measure. We hypothesized that, during exercise in the heat, the well-documented increase in skin blood flow for thermoregulation would lead to alterations in pulmonary blood flow and a subsequent fall in DLCO versus a thermoneutral condition. Nine healthy subjects (4 F/5M, 20-45years, VO2max 46.7 ± 5.8mL/kg/min) completed three 15-min stages including rest and during cycling at 20 and 40% of maximum workload (Wmax) in either thermoneutral (TN; 22.2 ± 0.6°C) or heat (HT; 39.4 ± 0.4°C) conditions. DLCO, minute ventilation (VE), oxygen consumption ([Formula: see text]), heart rate (HR), and core (TC) and skin temperature (Tsk) were measured. DLCO showed a significant interaction between exercise intensity and heat (P = 0.019); post hoc testing revealed that DLCO was higher at 40% of Wmax in HT vs. TN (53.2 ± 10.6 vs 50.0 ± 10.3mL/min/mmHg, P = 0.003) only. VE and [Formula: see text] showed no difference in HT vs. TN. HR was higher in HT vs. TN (P < 0.001). TC and Tsk showed a significant interaction between temperature and intensity (P < 0.05). The unexpected increase in DLCO during exercise in HT vs. TN conditions suggests a larger lung surface area for gas exchange, perhaps due to increased pulmonary capillary recruitment and/or distension secondary to a higher cardiac output (Q) in the heat. This study furthers our understanding of how heat exposure might impact pulmonary blood flow, specifically as assessed via DLCO.

Effects of Medications on Heat Loss Capacity in Chronic Disease Patients: Health Implications Amidst Global Warming.

Pharmacological agents used to treat or manage diseases can modify the level of heat strain experienced by chronically ill and elderly patients via different mechanistic pathways. Human thermoregulation is a crucial homeostatic process that maintains body temperature within a narrow range during heat stress through dry (i.e., increasing skin blood flow) and evaporative (i.e., sweating) heat loss, as well as active inhibition of thermogenesis, which is crucial to avoid overheating. Medications can independently and synergistically interact with aging and chronic disease to alter homeostatic responses to rising body temperature during heat stress. This review focuses on the physiologic changes, with specific emphasis on thermolytic processes, associated with medication use during heat stress. The review begins by providing readers with a background of the global chronic disease burden. Human thermoregulation and aging effects are then summarized to give an understanding of the unique physiologic changes faced by older adults. The effects of common chronic diseases on temperature regulation are outlined in the main sections. Physiologic impacts of common medications used to treat these diseases are reviewed in detail, with emphasis on the mechanisms by which these medications alter thermolysis during heat stress. The review concludes by providing perspectives on the need to understand the effects of medication use in hot environments, as well as a summary table of all clinical considerations and research needs of the medications included in this review. SIGNIFICANCE STATEMENT: Long-term medications modulate thermoregulatory function, resulting in excess physiological strain and predisposing patients to adverse health outcomes during prolonged exposures to extreme heat during rest and physical work (e.g., exercise). Understanding the medication-specific mechanisms of altered thermoregulation has importance in both clinical and research settings, paving the way for work toward refining current medication prescription recommendations and formulating mitigation strategies for adverse drug effects in the heat in chronically ill patients.

Mechanisms of Cardiovascular Changes of Phototherapy in Newborns with Hyperbilirubinemia.

During phototherapy of jaundiced newborns, vasodilation occurs in the skin circulation compensated by vasoconstriction in the renal and mesenteric circulation. Furthermore, there is a slight decrease in cardiac systolic volume, and blood pressure, as well as an increase in heart rate and discrete changes in the heart rate variability (HRV). The primary change during phototherapy is the skin vasodilation mediated by multiple mechanisms: 1) Passive vasodilation induced by direct skin heating effect of the body surface and subcutaneous blood vessels, modified by myogenic autoregulation. 2) Active vasodilation mediated via the mechanism provided by axon reflexes through nerve C-fibers and humoral mechanism via nitric oxide (NO) and endothelin 1 (ET-1). During and after phototherapy is a rise in the NO:ET-1 ratio. 3) Regulation of the skin circulation through the sympathetic nerves is unique, but their role in skin vasodilation during phototherapy was not studied. 4) Special mechanism is a photorelaxation independent of the skin heating. Melanopsin (opsin 4) - is thought to play a major role in systemic vascular photorelaxation. Signalling cascade of the photorelaxation is specific, independent of endothelium and NO. The increased skin blood flow during phototherapy is enabled by the restriction of blood flow in the renal and mesenteric circulation. An increase in heart rate indicates activation of the sympathetic system as is seen in the measures of the HRV. High-pressure, as well as low-pressure baroreflexes, may play important role in these adaptation responses. The integrated complex and specific mechanism responsible for the hemodynamic changes during phototherapy confirm adequate and functioning regulation of the neonatal cardiovascular system, including baroreflexes.

A preliminary investigation of the impact of artificially carbonated water bathing on canine skin physiological and barrier function.

The effect of carbon dioxide (CO2 )-rich water bathing on the skin has been studied extensively in humans. However, there have been few studies evaluating the impact of CO2 -rich water bathing on canine skin physiology and barrier functions. To evaluate the impact of artificially carbonated water (ACW) bathing on skin parameters in healthy beagles. Six healthy beagles with no history of skin disease. Body temperature, skin temperature, transepidermal water loss (TEWL), skin hydration and skin blood flow were evaluated before and after single ACW bathing (37°C, 20 min) with a CO2 concentration of >1000 ppm. After ACW bathing, skin blood flow significantly increased (p < 0.0001), yet there were no significant changes in body temperature (p=0.3124), skin temperature (p=0.4911), TEWL (p=0.5167) or skin hydration (p=0.3084). There were no adverse events during the trials. Artificially carbonated water water bathing could potentially increase skin blood flow without affecting skin temperature, body temperature and skin barrier function in dogs, similar to its effects in humans.

Autonomic thermoregulatory responses and subjective thermal perceptions upon the initiation of thermal behavior among resting humans in hot and humid environment

BackgroundWhile thermoregulatory behavior is critical for maintaining homeostasis, our knowledge of behavioral thermoeffectors in humid heat is limited compared to the control of autonomic thermoeffectors. The predictions that the frequency and duration of intensified humid heat events are expected to increase in the coming years underline this shortcoming. Therefore, this study aims to elucidate the activation of autonomic thermoregulatory responses and subjective thermal perceptions upon deciding to initiate thermal behavior in a hot and humid environment.MethodsTen young male adults participated in an experimental trial where local cooling was permitted at any time during the behavioral assessment during passive exposure to humid heat. The air temperature and relative humidity were kept at 33^{circ }C and 80%, respectively. Skin temperatures, core body temperature (T_{text {core}}), and skin blood flow (forearm, upper arm, and upper back) were obtained 120 s preceding thermal behavior. Local sweat rate (forearm and upper arm) and subjective thermal perceptions (neck and whole-body) upon thermal behavior initiation were also recorded.ResultsMean skin temperature ({overline{mathrm {T}}}_{text {sk}}) and T_{text {core}} increased prior to thermal behavior initiation (p= 0.002; p= 0.001). An increase in mean body temperature ({overline{mathrm {T}}}_{text {body}}) was also observed (p < 0.001). However, the initiation of thermal behavior is not preceded by an increase in skin blood flow (pge 0.154) and local sweat rate (pge 0.169). An increase in thermal discomfort and skin wetness perception was observed (ple 0.048; ple 0.048), while thermal sensation did not differ from the baseline (pge 0.357).ConclusionThese findings suggest that when given the opportunity to behaviorally thermoregulate in a hot and humid environment, changes in skin blood flow and sweat rate are not required for thermal behavior to be initiated in resting humans. Moreover, an increase in {overline{mathrm {T}}}_{text {sk}} and T_{text {core}}, which appears to cause an increase in thermal discomfort, precedes thermal behavior. In addition, an increase in {overline{mathrm {T}}}_{text {body}} leading up to thermal behavior initiation was observed, suggesting that changes in {overline{mathrm {T}}}_{text {body}} rather than {overline{mathrm {T}}}_{text {sk}} and T_{text {core}} alone mediate thermal behavior in humid heat. Collectively, the results of this study appear to support the hypothesis that the temporal recruitment of autonomic thermoeffectors follows an orderly manner based on their physiological cost.

An increase in skin blood flow induced by fluid challenge is associated with an increase in oxygen consumption in patients with circulatory shock.

To investigate whether an increase in skin blood flow (SBF) after fluid challenge was associated with an increase in oxygen consumption (VO2) in patients with circulatory shock. We studied 62 patients with shock who required fluid challenge. Using laser Doppler, we measured finger SBF at basal temperature (SBFBT) and after a thermal challenge test (SBFTCT), before and after a fluid challenge (500 ml of Plasmalyte®). In fluid responders (i.e., increase in cardiac index ≥15%), VO2 responders (VO2R) were those with a ≥15% increase in VO2. Of the 62 patients, 33 were fluid responders and 16 of these were VO2R. At baseline, VO2R had lower SBFBT (21[14-52] vs 83[24-116] PU, p = 0.03) and SBFTCT (2.1[1.2-3.3] vs 4.4[2.2-5.6] PU/°C, p = 0.02) than VO2 non-responders (VO2NR); hemodynamic variables were not significantly different. The increase in SBFBT (∆SBFBT) after fluid challenge was greater in VO2R than in VO2NR (141[83-174] vs 57[17-150]%, p = 0.03). Areas under the curves for baseline SBFTCT (0.83 ± 0.07 [0.68-0.98]) and ∆SBFBT (0.90 ± 0.05 [0.75-1.0]) to predict ∆VO2 ≥ 15% were higher than for other variables. A lower baseline SBFTCT and a greater ∆SBFBT can identify patients in whom VO2 will increase after fluid challenge, suggesting an improvement in cellular metabolism.

Reallocation of cutaneous and global blood circulation during sauna bathing through a closed-loop model

ObjectiveSauna bathing (SB) is an important strategy in cardiovascular protection, but there is no mathematical explanation for the reallocation of blood circulation during heat-induced superficial vasodilation. We sought to reveal such reallocation via a simulated hemodynamic model. MethodsA closed-loop cardiovascular model with a series of electrical parameters was constructed. The body surface was divided into seven blocks and each block was modeled by a lumped resistance. These resistances were adjusted to increase skin blood flow (SBF), with the aim of reflecting heat-induced vasodilation during SB. Finally, the blood pressure was compared before and after SB, and the blood flow inside the aorta and visceral arteries were also analyzed. ResultsWith increasing SBF in this model, the systolic, diastolic, and mean blood pressure in the arterial trunk decreased by 13–29, 18–36, and 19–37 mmHg, respectively. Despite the increase in the peak and mean blood flow in the arterial trunk, the diastolic blood flow reversal in the thoracic and abdominal aortas increased significantly. Nevertheless, the blood supply to the heart, liver, stomach, spleen, kidney, and intestine decreased by at least 25%. Moreover, the pulmonary blood flow increased significantly. ConclusionSimulated heat-induced cutaneous vasodilation in this model lowers blood pressure, induces visceral ischemia, and promotes pulmonary circulation, suggesting that the present closed-loop model may be able to describe the effect of sauna bathing on blood circulation. However, the increase of retrograde flow in the aortas found in this model deserves further examination.

Pulsatile flow in venous perforators of the lower limb.

Teaching traditionally asserts that the arterial pressure pulse is dampened across the capillary bed to the extent that pulsatility is nonexistent in the venous circulation of the lower limbs. Herein, we present evidence of transmission of arterial pulsations across the capillary network into perforator veins in the lower limbs of healthy, heat-stressed humans. Perforator veins are connections from the superficial veins that drain into the deep veins. When assessed using ultrasound at rest, they infrequently demonstrate flow, and a pulsatile flow waveform is not described. We investigated perforator vein pulsatility in 10 young, healthy volunteers who underwent passive heating by +2°C core body temperature via a hot-water-perfused suit, and 5 who also underwent active heating by +2°C via low-intensity cycling while wearing the hot-water-perfused suit. At +0.5°C increments in temperature, blood velocity in an ankle perforator vein was measured using duplex ultrasound. In all perforators with heating, sustained flow was demonstrated, with a pulsatile waveform that was synchronous with the cardiac cycle. The maximum velocity was 30 ± 13 cm/s with passive heating and approximately half with active heating (P = 0.04). The small veins of the skin at the ankle also demonstrated increased perfusion with pulsatility, seen with low-velocity microvascular imaging technology. We consider explanations for this pulsatility and conclude that it is propagated from the arterial inflow through the skin microcirculation as a result of increased dilatation and flow volume and that this is a normal response to increased skin blood flow.

Skin Blood Flow Responses to Acetylcholine, Local Heating, and to 60% VO2max exercise with and without Nitric Oxide inhibition, in Boys vs. Girls.

To determine sex-related differences in the skin blood flow (SkBF) response to exercise, local heating, and acetylcholine (ACh) in children, and to assess nitric oxide contribution to the SkBF response. Forearm SkBF during local heating (44°C), ACh iontophoresis, and exercise (30-min cycling and 60% of maximum oxygen consumption) was assessed, using laser Doppler fluxmetry, in 12 boys and 12 girls (7-13y old), with and without nitric oxide synthase inhibition, using Nω-nitro-L-arginine methyl ester iontophoresis. Local-heating-induced and ACh-induced SkBF increase were not different between boys and girls (local heating: 1445% [900%] and 1432% [582%] of baseline, P = .57; ACh: 673% [434%] and 558% [405%] of baseline, respectively, P = .18). Exercise-induced increase in SkBF was greater in boys than girls (528% [290%] and 374% [192%] of baseline, respectively, P = .03). Nω-nitro-L-arginine methyl ester blunted the SkBF response to ACh and during exercise (P < .001), with no difference between sexes. SkBF responses to ACh and local heat stimuli were similar in boys and girls, while the increase in SkBF during exercise was greater in boys. The apparent role of nitric oxide was not different between boys and girls. It is suggested that the greater SkBF response in boys during exercise was related to greater relative heat production and dissipation needs at this exercise intensity. The response to body size-related workload should be further examined.

Reactive hyperaemia augments local heat-induced skin hyperaemia.

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

The lower limb perforator veins in normal subjects

ObjectiveWith the developments in vascular ultrasound technology, the opportunity has arisen to examine in greater detail the distribution and behavior of the perforators in normal lower limbs and the implications in understanding their normal role. MethodsThe lower limbs of 20 healthy participants free of any cardiovascular or venous disease were examined. The anatomical characteristics and distribution as well as the functional features of all ultrasound-detectable lower limb venous perforators were evaluated in these normal limbs. Perforator flow was tested at rest, supine, sitting, standing, and with exercise. Comparisons were made between standard augmentation and isometric foot plantar flexion. ResultsTwenty individuals (13 females, 7 males; mean age, 36.9 ± 12 years) participated in the study. On average each limb had 14.2 (range, 8-21) perforators identified by ultrasound examination, with an average size of 1.3 ± 0.56 mm (range, 0.4-3.5 mm), most in the medial calf and those in the lower third were larger. On ultrasound examination, the valves were observed only within these larger direct perforators (17%; 18/105). All maneuvers resulted in flow which was only from superficial to the deep system and no two-way flow was observed. Spontaneous flow at rest occurred in a small proportion, but treadmill walking led to the recruitment of most perforators with spontaneous pulsatile flow at greatly increased velocities. The estimated total perforator volume flow could be increased by up to five-fold and accounting for as much as 80 mL/min in a leg. Isometric foot plantar flexion stopped any spontaneous flow and, on relaxation, resulted in a reproduceable short burst of inflow in the calf perforators. Augmentation by calf or foot cuff compression produced a brief variable inward, flow but this flow did not correlate with the perforator flow, with the more physiological maneuvers of isometric foot plantar flexion and exercise. ConclusionsThis study has shown that normal perforator veins in the leg are unidirectional from superficial to deep veins. Although few perforators have spontaneous flow at rest, most are recruited with exercise to substantially increase spontaneous perforator flow secondary to the increased skin blood flow. The augmentation maneuver is not comparable with more physiological activity. These normal features should be taken into account in the assessment of the abnormal perforator.

Menthol-induced activation of TRPM8 receptors increases cutaneous blood flow across the dermatome.

Topical menthol-based analgesics increase skin blood flow (SkBF) through transient receptor potential melastatin 8 (TRPM8) receptor-dependent activation of sensory nerves and endothelium-derived hyperpolarization factors. It is unclear if menthol-induced TRPM8 activation mediates a reflex change in SkBF across the dermatome in an area not directly treated with menthol. The purpose of this study was to determine the effects of localized topical menthol application on SkBF across a common dermatome. We hypothesized that SkBF would be increased with menthol at the site of application and across the dermatome (contralateral limb) through a spinal reflex mechanism. In a double blind, placebo controlled, cross-over design, 15 healthy participants (7 men; age=22±1yrs) were treated with direct application (3ml over 8×13cm) of 5% menthol gel (Biofreeze™) or placebo gel on the L4 dermatome, separated by 48h. Red blood cell flux was measured using laser Doppler flowmetry over the area of application, on the contralateral leg of the same dermatome, and in a separate dermatome (L5/S1) to serve as control. Cutaneous vascular conductance was calculated for each measurement site (CVC=flux/MAP). At baseline there were no differences in CVC between menthol and placebo gels, or among sites (all p>0.05). After 30±6min, CVC increased at the treated site with menthol (0.12±0.02 vs. 1.36±0.19flux/mmHg, p<0.01) but not the placebo (0.10±0.01 vs. 0.18±0.04flux/mmHg, p=0.91). There was a modest increase in CVC at the contralateral L4 dermatome with menthol gel (0.16±0.04 vs. 0.29±0.06flux/mmHg, p<0.01), but not placebo (0.11±0.02 vs. 0.15±0.03flux/mmHg, p=0.41). There was no effect on SkBF from either treatments at the L5/S1 control dermatome (both, p>0.05), suggesting the lack of a systemic response. In conclusion, menthol containing topical analgesic gels increased SkBF at the treated site, and modestly throughout the dermatome. These data suggest menthol-induced activation of the TRPM8 receptors induces an increase in SkBF across the area of common innervation through a localized spinal reflex mechanism.