Skin Blood Flux Research Articles

BRACHIAL, FEMORAL, AND SKIN HAEMODYNAMIC RESPONSES TO WALKING IN HOT CONDITIONS: COMPARISON BETWEEN MALES AND FEMALES

INTRODUCTION & AIMS Heat exposure induces acute changes in arterial function, but sex differences have not been fully addressed. METHODS Participants walked (5km/h; 2% incline) in a climate chamber (42°C;50%RH) for 120mins. Cutaneous microvascular function (laser doppler flowmetry), conduit artery haemodynamics (Doppler ultrasound) and core temperature were measured at baseline, and every 30min. RESULTS 14♂ and 15♀ completed 120min. At baseline, differences in core temperature (Tc) between males and females were not significant (37.2±0.1 vs 37.0±0.1°C; P=0.06). Across all 5 timepoints, females exhibited larger Tc than males (P=0.019). At baseline, males had larger brachial (3.89±0.11 vs 3.13±0.09mm, P<0.001) and femoral (6.22±0.16 vs 5.29±0.14mm, P=0.001) diameters than females. A significant interaction (P=0.047) indicated that brachial diameter increased more in response to heat exertion than in males, whereas no sex difference was apparent in femoral diameter change. Males and females had similar baseline brachial flows (♂80.1±11.2 vs ♀57.0±7.09ml/min, P=0.087), but males had larger baseline femoral flows (♂263.0±23.9 vs ♀151.5±18.6 ml/min, P=0.010). No sex differences were apparent in the terms of the increases in brachial or femoral flows. Finally, at baseline males and females had similar skin blood flux (♂22.6±2.7 vs ♀18.3±2.9PU), but males demonstrated larger increases during heat exertion (P=0.029). CONCLUSIONS Males exhibit larger baseline artery diameters and flows in vessel beds feeding active (femoral) and inactive (brachial) limbs. In response to heat exertion, men and women exhibit similar increases in conduit diameter and flow to active muscle beds (femoral responses). In the inactive forearms, which reflect thermoregulatory responses, females had larger brachial artery diameter changes, but blood flow responses were similar between the sexes and men demonstrated larger increases in skin perfusion. These data indicate that responses to heat exertion differ in the upper and lower limbs, with sex-differences apparent in each of these territories, and at distinct levels of the arterial hierarchy.

How do the skin barrier and microbiome adapt to the extra-uterine environment after birth? Implications for the clinical practice.

The multiple protective functions of the skin derive from the interactions between epithelial skin and immune cells as well as the commensal microbiota. Developed in the last trimester of intra-uterine life, the skin barrier adapts dynamically after birth. Specific differences in the structure and physiology have been disclosed between infant and adult skin. The stratum corneum of infants is thinner and structured by thicker corneocytes with a more anisotropic surface in comparison to adult skin. Lower levels of the natural moisturizing factor and its constituents, together with the increased protease activity in the epidermis result in dry baby skin and ongoing adaptation of the desquamation to the extra-uterine environment. Infant epidermis is characterized by an accelerated proliferation rate and clinically competent permeability barrier in term neonates, despite the higher baseline values of transepidermal water loss in infants. The skin surface of newborns is less acidic, which could increase susceptibility to diaper and atopic dermatitis. Immediately after birth, skin is colonized by commensal bacteria-a process dependent on the mode of delivery and of major importance for the maturation of the immune system. Skin bacterial diversity and dysbiosis have been related to different pathology such as atopic and seborrheic dermatitis. This paper focuses on the ongoing structural, functional and biochemical adaptation of the human skin barrier after birth. We discuss the interactions on the 'skin barrier/ microbiota/ immune system' axis and their role in the development of competent functional integrity of the epidermal barrier.

Laterality of blood perfusion in the lower extremities after drinking saline at different temperatures

Skin blood flux (SkBF) changes caused by drinking cold water are generally associated with vagal tone and osmotic factors in the digestive system. However, there is still a lack of relevant research on whether there are left and right differences in these SkBF change. In the current study, a total of 60 subjects were recruited. Skin blood perfusion of the bilateral lower extremities was recorded simultaneously before and after drinking saline of different temperatures saline by using Laser Doppler flowmetry (LDF). The electrogastrogram (EGG) was also monitored, and the dominant frequency of the EGG and heart rate variability were analyzed. The results indicated that after drinking saline, the laterality index of SkBF at the lower extremities was different and the laterality index changes of SkBF were mainly reflected in the frequency interval V (0.4–1.6 Hz). There was a weak negative correlation between the laterality index of endothelial NO-dependent component and change rate of root mean square of successive differences (RMSSD) after drinking 4 °C saline. However, after drinking 30 °C saline, there was a weak positive correlation between neurogenic component and RMSSD The distribution and regulation of bilateral blood flow are not symmetrical but exhibit a certain laterality.

Effect of reflex and mechanical decreases in skin perfusion on thermal- and agonist-induced eccrine sweating in humans.

In humans, skin blood flux (SkBF) and eccrine sweating are tightly coupled, suggesting common neural control and regulation. This study was designed to separate these two sympathetic nervous system end-organ responses via nonadrenergic SkBF-decreasing mechanical perturbations during heightened sudomotor drive. We induced sweating physiologically via whole body heat stress using a high-density tube-lined suit (protocol 1; 2 women, 4 men), and pharmacologically via forearm intradermal microdialysis of two steady-state doses of a cholinergic agonist, pilocarpine (protocol 2; 4 women, 3 men). During sweating induction, we decreased SkBF via three mechanical perturbations: arm and leg dependency to engage the cutaneous venoarteriolar response (CVAR), limb venous occlusion to engage the CVAR and decrease perfusion pressure, and limb arterial occlusion to cause ischemia. In protocol 1, heat stress increased arm cutaneous vascular conductance and forearm sweat rate (capacitance hygrometry). During heat stress, despite decreases in SkBF during each of the acute (3 min) mechanical perturbations, eccrine sweat rate was unaffected. During heat stress with extended (10 min) ischemia, sweat rate decreased. In protocol 2, both pilocarpine doses (ED50 and EMAX) increased SkBF and sweat rate. Each mechanical perturbation resulted in decreased SkBF but minimal changes in eccrine sweat rate. Taken together, these data indicate that a wide range of acute decreases in SkBF do not appear to proportionally decrease either physiologically- or pharmacologically induced eccrine sweating in peripheral skin. This preservation of evaporative cooling despite acutely decreased SkBF could have consequential impacts for heat storage and balance during changes in body posture, limb position, or blood flow restrictive conditions.

Comparison of laser speckle contrast imaging with laser Doppler perfusion imaging for tissue perfusion measurement.

Laser-based tissue perfusion monitoring techniques have been increasingly used in animal and human research to assess blood flow. However, these techniques use arbitrary units, and knowledge about their comparability is scarce. This study aimed to model the relationship between laser speckle contrast imaging (LSCI) and laser Doppler perfusion imaging (LDPI), for measuring tissue perfusion over a wide range of blood flux values. Fifteen healthy volunteers (53% female, median age 29 [IQR 22-40] years) were enrolled in this study. We performed iontophoresis with sodium nitroprusside on the forearm to induce regional vasodilation to increase skin blood flux. Besides, a stepwise vascular occlusion was applied on the contralateral upper arm to reduce blood flux. Both techniques were compared using a linear mixed model analysis. Baseline blood flux values measured by LSCI were 33 ± 6.5 arbitrary unit (AU) (Coefficient of variation [CV]=20%) and by LDPI 60 ± 11.5AU (CV=19%). At the end of the iontophoresis protocol, the regional blood flux increased to 724 ± 412% and 259 ± 87% of baseline measured by LDPI and LSCI, respectively. On the other hand, during the stepwise vascular occlusion test, the blood flux reduced to 212 ± 40% and 412 ± 177% of its baseline at LDPI and LSCI, respectively. A strong correlation was found between the LSCI and LDPI instruments at increased blood flux with respect to baseline skin blood flux; however, the correlation was weak at reduced blood flux with respect to baseline. LSCI and LDPI instruments are highly linear for blood flux higher than baseline skin blood flux; however, the correlation decreased for blood flux lower than baseline. This study's findings could be a basis for using LSCI in specific patient populations, such as burn care.

Effects of sensory nerve blockade on cutaneous microvascular responses to ischemia-reperfusion injury.

Examine the effects of sensory nerve blockade on cutaneous post-occlusive reactive hyperemia (PORH) and local thermal hyperemia (LTH) following prolonged upper limb ischemia. In nine males [28years (standard deviation:6)], volar forearm skin blood flux normalized to maximum vasodilation (%SkBFmax) was assessed at control (CTRL) and sensory nerve blockade (EMLA) treated sites during the PORH response following 20-min of complete arm ischemia and during rapid LTH (33-42°C, 1°C·20s-1, held for ~30-min+20-min at 44°C) before and after ischemia-reperfusion (IR) injury. EMLA increased mean [95% confidence-interval] PORH amplitude by 21%SkBFmax ([9,33]; p=0.003), delayed time to peak by 111s ([40,182]; p=0.007) and increased area under the curve by 19,462%SkBFmax·s ([11,346,27,579]; p<0.001) compared to CTRL. For LTH, EMLA delayed onset time by 76s ([46,106]; p<0.001) Pre-IR and by 46s ([27,65]; p<0.001) Post-IR compared to CTRL. Post-IR onset time was delayed for CTRL by 26s ([8,43]; p=0.007), but was not different for EMLA (p>0.050) compared to Pre-IR. EMLA delayed time to initial peak by 24s ([4,43]; p=0.022, Main time effect) and it attenuated the initial peak by 27%SkBFmax ([12,43]; p=0.002) Pre-IR and by 16%SkBFmax ([3,29]; p=0.020) post-IR compared to CTRL. Post-IR, the initial peak was not different for CTRL (p>0.050), but it was increased by 16%SkBFmax ([5,26]; p=0.005) for EMLA compared to Pre-IR. Neither EMLA nor IR altered the steady-state heating plateau (all p>0.050). For the current model of IR injury, sensory nerves appear to have a negligible influence on the LTH response in non-glabrous forearm skin once vasodilation has been initiated.

The Relationship Between Blood Perfusion in the Lower Extremities and Heart Rate Variability at Different Positions.

Previous studies have explored the relationship between the complexity of local blood flow signals and heart rate variability (HRV) under different thermal stimulations. However, the relationship between the complexity of local blood flow signals and HRV in different positions is not clear. In this study, healthy participants were placed in different body positions. The bilateral blood flux and ECG were monitored, and refined composite multiscale entropy (RC MSE) and refined composite multiscale fuzzy entropy (RC MFE) were used to measure the complexity of the local blood flux. The sample entropy was calculated to evaluate the HRV complexity. The change of body position did not affect the time domain or frequency domain of HRV, but did reverse the blood flux laterality of the lower extremities. Furthermore, there was a negative correlation between the complexity of right-side blood flux and sample entropy of HRV when the participant was in the -10 degrees position. These results provide a new perspective of the relationship between skin blood flux signals and cardiac function.

Treprostinil iontophoresis in systemic sclerosis-related digital skin ulcers: A single ascending dose safety study

Digital skin ulcers are a severe complication of systemic sclerosis(SSc). The first-line treatment is intravenous iloprost, but it induces dose-limiting adverse effects. Local administration of treprostinil through skin iontophoresis may be a safe alternative. We conducted a two-stage, randomized, placebo-controlled single ascending dose study in healthy volunteers and patients with SSc-related digital ulcer (SSc-DU). We further explored the effect of the procedure on skin blood flux. The objectives were to assess the safety of an iontophoresis of treprostinil hydrogel administered on healthy volunteers finger pad, leg and foot and asses the safety of ascending doses in patients with SSc-DU. In a first group of healthy subjects, treprostinil and placebo iontophoresis were performed at 3 different locations (i.e. 6 skin sites): the sole of the foot, the leg, and the fingers. We used a 1 mg/mL hydrogel of treprostinil. We then randomly treated SSc-DUs in a 3/1 ratio treprostinil or placebo respectively. We used concentrations from 0.1 to 1 mg/mL. All adverse events were recorded and rated (according to the CTCAE), while skin microvascular blood flux was recorded with laser speckle contrast imaging. Among the 12 healthy volunteers, we observed 60 local adverse effects: burns, skin pain, erythema and pruritus, graded 1 or 2 on the 5-point CTCAE scale. Treprostinil iontophoresis significantly increased skin blood flux on the leg (AUC0-4 h at 88460 ± 6436 versus 12730 ± 3397%BL.min respectively, P < 0.001) and on the sole of the foot (AUC0-3 h at 20124 ± 6119 versus 3142 ± 3036% BL.min respectively, P = 0.018) with a trend on the finger (AUC0-3 h was 10773 ± 4888). Among five patients with SSc-UD, 2 resolutive local adverse effects were reported. Iontophoresis of treprostinil was safe in SSc patients with digital ulcers. Treprostinil at 1 mg/mL will be used in the next study, i.e. repeated iontophoresis in SSc-related ulcer.

Alterations in cutaneous microvascular function at high altitude in lowlanders and highlanders

Microvascular function is impaired in lowlanders at high altitude; however, this impairment was gauged using post‐occlusive reactive hyperemia and the contribution of nitric oxide (NO) to cutaneous vasodilation at high altitude remains unknown. Low molecular O2 at high altitude leads to production of reactive oxygen species (ROS) and reduced NO bioavailability. We therefore tested the hypothesis that vasodilation during a standard local heating protocol, and thus cutaneous microvascular function, is impaired in lowlanders at high altitude by ROS. We further tested whether lifelong residence at high altitude alters microvascular function compared to lowlanders. Four intradermal microdialysis membranes were inserted in the forearms of 11 male lowlanders [age: 30 (8) years; BMI: 24 (2) kg·m−2] at sea level and after two weeks at 4340 m in Cerro de Pasco, Peru. Andean highlanders [n=11; age: 26 (5) years; BMI: 24 (2) kg·m−2] residing permanently in Cerro de Pasco were also tested. The four sites were randomized and pre‐treated with infusions of 1) lactated Ringer's solution (control), 2) 100 μM Apocynin (NADPH oxidase inhibitor), 3) 10 μM Tempol (superoxide scavenger), and 4) 10 μM Allopurinol (xanthine oxidase inhibitor). Skin blood flux was measured continuously at each site via laser‐Doppler flowmetry during the 39°C local heating (NO‐dependent plateau phase), 20 mM L‐NAME (NO synthase inhibitor), and 44°C local heating combined with 28 mM sodium nitroprusside infusion to achieve maximal vasodilation. Data are presented as cutaneous vascular conductance (CVC; flux/mean arterial pressure) as a percentage of maximum.There was a main group effect (P&lt;0.001) on CVC during 39°C heating with impaired vasodilation in both lowlanders at high altitude and in Andeans [control site: 54 (14) vs. 50 (24)%, respectively] compared to lowlanders at sea level [control site: 73 (19)%]. Similarly, the NO contribution to vasodilation during the 39°C plateau portion (i.e. effect of L‐NAME) was impaired (main group effect P&lt;0.001) in lowlanders after 2 weeks at high altitude compared to sea level [control site: 41 (11) vs 49 (10)%, respectively], and this impairment was more pronounced in Andeans [control site: 32 (21)%]. There was no influence of ROS pathways, assessed via antioxidant infusions, on cutaneous vasodilation throughout the protocol in any group (all main drug effects P&gt;0.05). When values were pooled from both groups and altitudes, local heating plateau CVC (r2=0.18, P=0.02) and the NO contribution to vasodilation (r2=0.13, P=0.04) were both positively correlated with oxygen‐hemoglobin saturation.These results indicate that high altitude impairs NO‐mediated vasodilation independent of a ROS mechanism but is associated with oxygen‐hemoglobin desaturation. The extent of microvascular impairment is greater in lifelong high altitude residents.Support or Funding InformationCanada Research Chairs ProgramThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Multi‐domain analysis of microvascular flow motion dynamics in NAFLD

To determine whether analysis of microvascular network perfusion using complexity-based methods can discriminate between groups of individuals at an increased risk of developing CVD. Data were obtained from laser Doppler recordings of skin blood flux at the forearm in 50 participants with non-alcoholic fatty liver disease grouped for absence (n=28) or presence (n=14) of type 2 diabetes and use of calcium channel blocker medication (n=8). Power spectral density was evaluated and Lempel-Ziv complexity determined to quantify signal information content at single and multiple time-scales to account for the different processes modulating network perfusion. Complexity was associated with dilatory capacity and respiration and negatively with baseline blood flux and cardiac band power. The relationship between the modulators of flowmotion and complexity of blood flux is shown to change with time-scale improving discrimination between groups. Multiscale Lempel-Ziv achieved best classification accuracy of 86.1%. Time and frequency domain measures alone are insufficient to discriminate between groups. As cardiovascular disease risk increases, the degree of complexity of the blood flux signal reduces, indicative of a reduced temporal activity and heterogeneous distribution of blood flow within the microvascular network sampled. Complexity-based methods, particularly multiscale variants, are shown to have good discriminatory capabilities.

Sustained vasomotor control of skin microcirculation in Sherpas versus altitude-naive lowlanders: Experimental evidence from Xtreme Everest 2.

What is the central question of this study? Do Sherpa highlanders, when exposed to graded hypobaric hypoxia, exhibit enhanced vasomotor and neurovascular control to maintain microcirculatory flux, and thus tissue oxygenation, when compared with altitude-naive lowlanders? What is the main finding and its importance? Sherpas, when exposed to hypobaric hypoxia at high altitude, demonstrated superior preservation of their peripheral microcirculatory perfusion, a greater oxygen unloading rate and sustained microvascular reactivity with enhanced vasomotion, when compared with altitude-naive lowlanders. These differences have not been reported previously and may improve our understanding of the multifactorial responses to sustained environmental hypoxia. Enhanced oxygen delivery, consequent to an increased microvascular perfusion, has been postulated to play a key role in the physiological adaptation of Tibetan highlanders to the hypobaric hypoxia encountered at high altitude. We tested the hypothesis that Sherpas, when exposed to graded hypobaric hypoxia, demonstrate enhanced vasomotor and neurovascular control to maintain microcirculatory flux, and thus tissue oxygenation, when compared with altitude-naive lowlanders. Eighty-three lowlanders [39 men and 44 women, 38.8(13.1)years old; mean(SD)] and 61 Sherpas [28 men and 33 women, 27.9(6.9)years old] were studied on ascent to Everest Base Camp over 11 days. Skin blood flux and tissue oxygen saturation were measured simultaneously using combined laser Doppler fluximetry and white light spectroscopy at baseline, 3500 and 5300m. In both cohorts, ascent resulted in a decline in the sympathetically mediated microvascular constrictor response (P<0.001), which was more marked in lowlanders than in Sherpas (P<0.001). The microvascular dilator response evaluated by postocclusive reactive hyperaemia was significantly greater in Sherpas than in lowlanders at all sites (P<0.002). Spectral analysis of the blood flux signals revealed enhanced myogenic (vasomotion) activity in Sherpas, which was unaffected by ascent to 5300m. Although skin tissue oxygenation was lower in Sherpas than in lowlanders, the oxygen unloading rate was faster, and deoxyhaemoglobin levels higher, at all altitudes.Together, these data suggest that Sherpas, when exposed to hypobaric hypoxia, demonstrated superior preservation of peripheral microcirculatory perfusion compared with altitude-naive lowlanders. The physiological differences in local microvasculature vasomotor and neurovascular control may play a key role in Sherpa adaptation to high-altitude hypobaric hypoxia by sustaining local perfusion and tissue oxygenation.

Exploring the Relationship between Blood Flux Signals and HRV following Different Thermal Stimulations using Complexity Analysis

To investigate the relationship between local blood flux and heart rate variability following different thermal stimulations, healthy subjects were recruited and subject to different thermal stimulations on the right forearm. Multiscale entropy and multiscale fuzzy entropy were used to measure the complexity of the local blood flux, and the approximate entropy was calculated to evaluate the HRV complexity. The results indicated that thermal stimulation significantly increased local blood flux and that different temperature stimulations resulted in different complexities in local blood flux. A 42 °C or 44 °C thermal stimulation, other than stimulations below 42 °C, resulted in a moderate correlation between local blood flux and heart rate variability complexity. The results provide a new perspective in terms of complexity to explore the relationship between skin blood flux signals and cardiac function.

In Shackleton's trails: Central and local thermoadaptive modifications to cold and hypoxia after a man-hauling expedition on the Antarctic Plateau

Cold and hypoxia constitute the main environmental stressors encountered on the Antarctic Plateau. Hence, we examined whether central and/or peripheral acclimatisation to the combined stressors of cold and hypoxia would be developed in four men following an 11-day man-hauling expedition on this polar region. Before and after the journey, participants performed a static whole-body immersion in 21 °C water, during which they were breathing a hypoxic gas (partial pressure of inspired O2: ~97 mmHg). To evaluate their local responses to cold, participants also immersed the hand into 8 °C water for 30 min, while they were whole-body immersed and mildly hypothermic [i.e. 0.5 °C fall in rectal temperature (Trec) from individual pre-immersion values]. Trec and skin temperature (Tsk), skin blood flux, and oxygen uptake (reflecting shivering thermogenesis) were monitored throughout. The polar expedition accelerated by ~14 min the drop in Trec [final mean (95% confidence interval) changes in Trec: Before = −0.94 (0.15) °C, After: − 1.17 (0.23) °C]. The shivering onset threshold [Before: 19 (22) min, After: 25 (19) min] and gain [Before: − 4.19 (3.95) mL min−1 kg−1, After: − 1.70 (1.21) mL min−1 kg−1] were suppressed by the expedition. Tsk did not differ between trials. The development of a greater post-expedition hypothermic state did not compromise finger circulation during the hand-cooling phase. Present findings indicate therefore that a hypothermic pattern of cold acclimatisation, as investigated in hypoxia, was developed following a short-term expedition on the South Polar Plateau; an adaptive response that is characterised mainly by suppressed shivering thermogenesis, and partly by blunted cutaneous vasoconstriction.

Response of Blood Perfusion at ST 36 Acupoint after Drinking Cold Glucose or Saline Injection.

Skin blood flux (SkBF) changes caused by drinking cold water are generally associated with vagal tone and osmotic factors in digestive system. According to acupuncture theory, change of SkBF at ST 36 might reflect the functional changes of digestive system. The aim of this study is to analyze the changes of SkBF after drinking 3°C 0.9% saline or 5% glucose injection by monitor blood flux at bilateral ST 36. The results indicated that, after drinking different cold water, the change ratio of SkBF at right side ST 36 has been different. Because all solutions have the same temperature (3°C) and both saline and glucose solution have the same osmolality, suggesting that the SkBF changes resulting from drinking cold water are not regulated just by the vagal tone and osmolality, there must have been other factors. These results have not been consistent with the frequency domain results of heart rate variability (HRV) analysis. Coherence analysis of blood flux signals at bilateral ST 36 indicated that there have been different coherence-frequency curves among different groups in special frequency bands, which suggested that coherence analysis might provide a potential tool to evaluate different status.

Cutaneous exposure to hypoxia does not affect skin perfusion in humans.

Experiments have indicated that skin perfusion in mice is sensitive to reductions in environmental O2 availability. Specifically, a reduction in skin-surface PO2 attenuates transcutaneous O2 diffusion, and hence epidermal O2 supply. In response, epidermal HIF-1α expression increases and facilitates initial cutaneous vasoconstriction and subsequent nitric oxide-dependent vasodilation. Here, we investigated whether the same mechanism exists in humans. In a first experiment, eight males rested twice for 8h in a hypobaric chamber. Once, barometric pressure was reduced by 50%, while systemic oxygenation was preserved by O2 -enriched (42%) breathing gas (HypoxiaSkin ), and once barometric pressure and inspired O2 fraction were normal (Control1 ). In a second experiment, nine males rested for 8h with both forearms wrapped in plastic bags. O2 was expelled from one bag by nitrogen flushing (AnoxiaSkin ), whereas the other bag was flushed with air (Control2 ). In both experiments, skin blood flux was assessed by laser Doppler on the dorsal forearm, and HIF-1α expression was determined by immunohistochemical staining in forearm skin biopsies. Skin blood flux during HypoxiaSkin and AnoxiaSkin remained similar to the corresponding Control trial (P=0.67 and P=0.81). Immunohistochemically stained epidermal HIF-1α was detected on 8.2±6.1 and 5.3±5.7% of the analysed area during HypoxiaSkin and Control1 (P=0.30) and on 2.3±1.8 and 2.4±1.8% during AnoxiaSkin and Control2 (P=0.90) respectively. Reductions in skin-surface PO2 do not affect skin perfusion in humans. The unchanged epidermal HIF-1α expression suggests that epidermal O2 homoeostasis was not disturbed by HypoxiaSkin /AnoxiaSkin , potentially due to compensatory increases in arterial O2 extraction.

Effects of mild hypohydration on cooling during cold-water immersion following exertional hyperthermia.

We investigated the effects of mild hypohydration compared to euhydration on the cooling efficacy of cold-water immersion (CWI). Fourteen participants (eight male, six female; age 26 ± 5 years; ht 1.77 ± 0.08 m; wt 72.2 ± 8.8 kg; 20.6 ± 7.4 % body fat) completed one euhydrated (EU) trial followed by one hypohydrated trial (HY; via 24 h fluid restriction) in an environmental chamber (33.6 ± 0.9 °C, 55.8 ± 1.7 % RH). Volitional exercise was performed in a manner that matched end-exercise rectal temperature (T re) through repeating exercise mode and intensity. Participants were then immersed in ice water (2.0 ± 0.8 °C) until T re reached 38.1 °C or for a maximum of 15 min. T re, heart rate (HR), skin blood flux (SBF) and mean skin temperature (T sk) were monitored continuously during cooling. Pre-cooling body mass was decreased in the HY trial (-2.66 ± 1.23 % body mass) and maintained in the EU trial (-0.66 ± 0.44 %) compared to baseline mass (P < 0.001). Cooling rates were faster when EU (0.14 ± 0.05 °C/min) compared to HY (0.11 ± 0.05 °C/min, P = 0.046). HR, SBF, and T sk were not different between EU and HY trials (P > 0.05), however, all variables significantly decreased with immersion independent of hydration status (P < 0.001). The primary finding was that hypohydration modestly attenuates the rate of cooling in exertionally hyperthermic individuals. Regardless of hydration status, the cooling efficacy of CWI was preserved and should continue to be utilized in the treatment of exertional hyperthermia.

The contribution of sensory nerves to the onset threshold for cutaneous vasodilatation during gradual local skin heating of the forearm and leg

During local skin heating, the temporal onset of vasodilatation is delayed in the leg compared to the forearm, and sensory nerve blockade abolishes these differences. However, previous work using rapid skin heating did not allow for determination of sensory nerve influences on temperature thresholds for vasodilatation. Two sites were examined on both the forearm and leg, one control (CTRL), and one treated for sensory nerve blockade (EMLA). Skin blood flux was monitored using laser-Doppler probes, with heaters controlling local skin temperature (Tloc). Tloc was increased from 32–44°C (+1°C·10min−1). Stimulus–response curves were constructed by fitting a four-parameter logistic function. EMLA significantly increased Tloc onset in the forearm (CTRL=35.3±0.4°C; EMLA=36.8±0.7°C) and leg (CTRL=36.5±0.4°C; EMLA=38.4±0.5°C; both P<0.05). At both CTRL and EMLA, Tloc onset was higher in the leg compared to the forearm (both P<0.05). In the forearm, median effective temperature to elicit 50% vasodilatation (ET50) was similar between sites (CTRL=39.7±0.3°C; EMLA=40.2±0.4°C; P=0.09); however, in the leg, EMLA significantly increased ET50 (CTRL=40.2±0.3°C; EMLA=41.0±0.3°C)(P<0.05). At CTRL sites, no limb difference was observed for ET50 (P=0.06); however, with EMLA, ET50 was significantly higher in the leg (P<0.05). EMLA significantly increased the gain of the slope at the forearm, (CTRL=0.31±0.01%CVCmax·°C−1; EMLA=0.45±0.07%CVCmax·°C−1), and leg (CTRL=0.37±0.05%CVCmax·°C−1; EMLA=0.54±0.04%CVCmax·°C−1)(both P<0.05). At CTRL sites, the gain was significantly higher in the leg (P<0.05); however, for EMLA, no significant limb difference existed (P=0.10). These data indicate that the onset of vasodilatation occurs at a lower temperature in the forearm than the legs, and sensory nerves play an important role in both limbs.

Combined facial heating and inhalation of hot air do not alter thermoeffector responses in humans.

The influence of thermoreceptors in human facial skin on thermoeffector responses is equivocal; furthermore, the presence of thermoreceptors in the respiratory tract and their involvement in thermal homeostasis has not been elucidated. This study tested the hypothesis that hot air directed on the face and inhaled during whole body passive heat stress elicits an earlier onset and greater sensitivity of cutaneous vasodilation and sweating than that directed on an equal skin surface area away from the face. Six men and two women completed two trials separated by ∼1 wk. Participants were passively heated (water-perfused suit; core temperature increase ∼0.9°C) while hot air was directed on either the face or on the lower leg (counterbalanced). Skin blood flux (laser-Doppler flowmetry) and local sweat rate (capacitance hygrometry) were measured at the chest and one forearm. During hot-air heating, local temperatures of the cheek and leg were 38.4 ± 0.8°C and 38.8 ± 0.6°C, respectively (P = 0.18). Breathing hot air combined with facial heating did not affect mean body temperature onsets (P = 0.97 and 0.27 for arm and chest sites, respectively) or slopes of cutaneous vasodilation (P = 0.49 and 0.43 for arm and chest sites, respectively), or the onsets (P = 0.89 and 0.94 for arm and chest sites, respectively), or slopes of sweating (P = 0.48 and 0.65 for arm and chest sites, respectively). Based on these findings, respiratory tract thermoreceptors, if present in humans, and selective facial skin heating do not modulate thermoeffector responses during passive heat stress.

Laser-Doppler microvascular measurements in the peri-implant areas of different osseointegrated bone conductor implant systems.

The objective of this study was to evaluate the impact of hydroxyapatite coating of newly designed osseointegrated fixtures' abutments on the postoperative complication rates. The integrity of peri-implant microcirculation was used as a marker to compare tissue viability after different surgical techniques. Laser-Doppler Flowmetry (LDF) measures alone, and coupled with heat provocation tests were applied to test the different microcircular patterns. Measures for 17 consecutively implanted patients (8 women, 9 men, ages ranged from 18 to 77 years) were recruited; seven with soft tissue reduction (STR); and 10 with soft tissue preservation (STP).Thirteen non-operated retro-auricular areas were examined as naive controls. In isotherm conditions the baseline blood flow remained stable in all groups. The naive control patients demonstrated significant changes of blood flux in the intact skin. The non-implanted yet previously operated contralateral sides of the patients demonstrated marginally lower (p = 0.09) blood flux index. The STR sides however, showed significantly lower (average 217 %) provoked blood flux compared to controls (p < 0.001). At the STP sides a maladaptation could be observed (average 316 %) compared to the contralateral sides (p = 0.53). STP sides demonstrated a significantly better blood flow improvement compared to the STR sides (p = 0.02). These results suggest a favorable postoperative condition of vascular microcirculation after STP, than after STR surgery. The possibly faster wound healing and lower potential complication rate may widen the inclusion criteria and maybe beneficial for the patient compliance with a better quality-of-life.

To reheat, or to not reheat: that is the question: The efficacy of a local reheating protocol on mechanisms of cutaneous vasodilatation

The aim of this study is to determine the effect of repeated bouts of local skin heating on the roles of nitric oxide synthase (NOS) and sympathetic nerves in cutaneous vasodilatation. In 3 repeated-heating protocols skin blood flux of the forearm and leg was measured using laser-Doppler flowmetry and data are presented as cutaneous vascular conductance (CVC; flux/blood pressure). Local heating was performed from 33°C (thermoneutral) to 42°C at 0.5°C·10s−1, allowed to cool passively for ~60-min, then reheated at the same rate. In protocol 1, CVC was measured in response to repeated heating. In protocol 2, NOS was inhibited with NG-nitro-l-arginine methyl ester (L-NAME) and in protocol 3, sympathetic nerve blockade was achieved with bretylium tosylate (BT), both infused via intradermal microdialysis. In protocol 1, there were no differences (P>0.05) in CVC at either the forearm (88±4 vs. 86±4%max) or the leg (97±4 vs. 96±6%max) between heating bouts. In protocol 2, no differences (P>0.05) in CVC were observed between heating bouts at L-NAME treated sites at either the forearm (55±3 vs. 51±4%max) or the leg (71±3 vs. 70±4%max) . In protocol 3, there were differences (P<0.001) between BT treated sites when comparing the first and second bouts of heating for both the forearm (75±3 vs. 88±4%max) and the leg (79±3 vs. 97±4%max). The effect of sympathetic blockade on CVC responses to local heating was abolished following repeated bouts of heating. Consequently, it is our suggestion that when examining mechanisms of skin blood flow control, investigators use single bouts of local heating.