Prolonged (9 h) poikilocapnic hypoxia (12% O2) augments cutaneous thermal hyperaemia in healthy humans

Hypoxic Training Ameliorates Skeletal Muscle Microcirculation Vascular Function in a Sirt3-Dependent Manner

Hypoxic training improves the microcirculation function of human skeletal muscle, but its mechanism is still unclear. Silent information regulator 2 homolog 3 (Sirt3) can improve mitochondrial function and oxidative status. We aimed to examine the role of Sirt3 in the process of hypoxic training, which affects skeletal muscle microcirculation. C57BL/6 mice were assigned to control (C), hypoxic training (HT), Sirt3 inhibitor 3-(1H-1,2,3-triazol-4-yl) pyridine (3-TYP), and 3-TYP + hypoxic training (3-TYP + HT) groups (n = 6/group). Sirt3 inhibition was induced by intraperitoneal injection of Sirt3 inhibitor 3-TYP. After 6 weeks of intervention, microcirculatory capillary formation and vasomotor capacity were evaluated using immunofluorescence, Western blot, biochemical tests, and transmission electron microscopy (TEM). Laser Doppler flowmetry was used to evaluate skeletal muscle microcirculation blood flow characteristics. Six weeks of hypoxic training enhanced skeletal muscle microcirculation function and increased microcirculatory vasodilation capacity and capillary formation. After the pharmacological inhibition of Sirt3, the reserve capacity of skeletal muscle microcirculation was reduced to varying degrees. After the inhibition of Sirt3, mice completed the same hypoxic training, and we failed to observe the microcirculation function adaptation like that observed in hypoxic training alone. The microcirculation vasodilation and the capillaries number did not improve. Hypoxic training improved skeletal muscle microcirculation vasodilation capacity and increased skeletal muscle microcirculation capillary density. Sirt3 is involved in the adaptation of skeletal muscle microcirculation induced by hypoxic training.

Reactive hyperemia augments local heat-induced skin hyperemia

NEW FINDINGS

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 noninvasive monitoring of the skin microcirculation and its ability to vasodilate. Does reactive hyperemia augment the increase in skin blood flow elicited by local heating? What is the main finding and its importance? The results of this study show that the addition of reactive hyperemia to local heating results in greater vasodilation than heating alone. Thus, reactive hyperemia can augment local heat-induced hyperemia in the skin.

ABSTRACT

The skin circulation has been proposed as a model of generalized microvascular function which could be monitored noninvasively using laser doppler flowmetry (LDF). The response to heat hyperemia (HH) is commonly used to monitor disease or treatment related changes in microvascular function. We hypothesized that reactive hyperemia would augment the increase in skin blood flow elicited by local heating. Fourteen healthy young adults were subjected to 3 different conditions: reactive hyperemia (RH; skin temperature controlled at 33°C), heat hyperemia (HH; 42°C held for 40 minutes), and HH+RH. Two Peltier-controlled thermomodules with laser LDF probes were placed on the right forearm to continuously monitor skin blood flow. A cuff was placed on the right upper arm to elicit RH by inflation to 220 mmHg for 5 minutes. This procedure was performed with skin temperature at 33°C and again after 40 min 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) above baseline values. LDF and CVC values were significantly higher during HH+RH when compared to RH or HH alone (p<0.0001). In summary, HH+RH resulted in greater vasodilation when compared to HH or RH alone. These results indicate that RH can augment local heat-induced hyperemia in the skin. This article is protected by copyright. All rights reserved.

Na+-K+-ATPase plays a major role in mediating cutaneous thermal hyperemia achieved by local skin heating to 39°C

Na⁺-K⁺-ATPase is integrally involved in mediating cutaneous vasodilation during an exercise-heat stress, which includes an interactive role with nitric oxide synthase (NOS). Here, we assessed if Na⁺-K⁺-ATPase also contributes to cutaneous thermal hyperemia induced by local skin heating, which is commonly used to assess cutaneous endothelium-dependent vasodilation. Furthermore, we assessed the extent to which NOS contributes to this response. Cutaneous vascular conductance (CVC) was measured continuously at four forearm skin sites in 11 young adults (4 women). After baseline measurement, local skin temperature was increased from 33°C to 39°C to induce cutaneous thermal hyperemia. Once a plateau in CVC was achieved, each skin site was continuously perfused via intradermal microdialysis with either: 1) lactated Ringer solution (control), 2) 6 mM ouabain, a Na⁺-K⁺-ATPase inhibitor, 3) 20 mM l-NAME, a NOS inhibitor, or 4) a combination of both. Relative to the control site, CVC during the plateau phase of cutaneous thermal hyperemia (∼50% max) was reduced by the lone inhibition of Na⁺-K⁺-ATPase (-19 ± 8% max, P = 0.038) and NOS (-32 ± 4% max, P < 0.001), as well as the combined inhibition of both (-37 ± 9% max, P < 0.001). The magnitude of reduction was similar between NOS inhibition alone and combined inhibition (P = 1.000). The administration of both Na⁺-K⁺-ATPase and NOS inhibitors fully abolished the plateau of CVC with values returning to preheating baseline values (P = 0.439). We show that Na⁺-K⁺-ATPase contributes to cutaneous thermal hyperemia during local skin heating to 39°C, and this response is partially mediated by NOS.NEW & NOTEWORTHY Cutaneous thermal hyperemia during local skin heating to 39°C, which is highly dependent on nitric oxide synthase (NOS), is frequently used to assess endothelium-dependent cutaneous vasodilation. We showed that Na⁺-K⁺-ATPase mediates the regulation of cutaneous thermal hyperemia partly via NOS-dependent mechanisms although a component of the Na⁺-K⁺-ATPase modulation of cutaneous thermal hyperemia is NOS independent. Thus, as with NOS, Na⁺-K⁺-ATPase may be important in the regulation of cutaneous endothelial vascular function.

Global Reach 2018: Nitric oxide-mediated cutaneous vasodilation is reduced in chronic, but not acute, hypoxia independently of enzymatic superoxide formation

We tested the hypotheses that 1) cutaneous microvascular function is impaired by acute normobaric and chronic hypobaric hypoxia and 2) that the superoxide free radical (via NADPH oxidase or xanthine oxidase) contributes to this impairment via nitric oxide (NO) scavenging. Local heating-induced cutaneous hyperemia (39 °C) was measured in the forearm of 11 male lowlanders at sea level (SL) and following 14-18 days at high altitude (HA; 4340 m in Cerro de Pasco, Peru), and compared to 11 highlanders residing permanently at this elevation. Cutaneous vascular conductance (CVC; laser-Doppler flux/mean arterial pressure) was not different during 39 °C [control site: 73 (19) vs. 71 (18)%max; P = 0.68] between normoxia and acute normobaric hypoxia (F_IO₂ = 0.125; equivalent to HA), respectively. At HA, CVC was reduced during 39 °C in lowlanders compared to SL [control site: 54 (14) vs. 73 (19)%max; P < 0.01] and was lower in Andean highlanders compared to lowlanders at HA [control site: 50 (24) vs. 54 (14)%max; P = 0.02]. The NO contribution to vasodilation during 39 °C (i.e., effect of NO synthase inhibition) was reduced in lowlanders at HA compared to SL [control site: 41 (11) vs 49 (10)%max; P = 0.04] and in Andean highlanders compared to lowlanders at HA [control site: 32 (21) vs. 41 (11)%max; P = 0.01]. Intradermal administration (cutaneous microdialysis) of the superoxide mimetic Tempol, inhibition of xanthine oxidase (via allopurinol), or NADPH oxidase (via apocynin) had no influence on cutaneous endothelium-dependent dilation during any of the conditions (all main effects of drug P > 0.05). These results suggest that time at HA impairs NO-mediated cutaneous vasodilation independent of enzymatic superoxide formation.

The deleterious effects of acute hypoxia on microvascular and large vessel endothelial function

NEW FINDINGS

What is the central question of this study? The aim was primarily to determine the effect of hypoxia on microvascular function and secondarily whether superior cardiorespiratory fitness is protective against hypoxia-induced impairment in vascular function. What is the main finding and its importance? Hypoxia reduced endothelium-dependent but not endothelium-independent microvascular function. The extent of impairment was twofold higher in the microcirculation compared with the large blood vessels. This study suggests that individuals with superior cardiorespiratory fitness might preserve microvascular function in hypoxia. These findings highlight the sensitivity of the microvascular circulation to hypoxia.

ABSTRACT

Hypoxia is associated with diminished bioavailability of the endothelium-derived vasodilator, nitric oxide (NO). Diminished NO bioavailability can have deleterious effects on endothelial function. The endothelium is a heterogeneous tissue; therefore, a comprehensive assessment of endothelial function is crucial to understand the significance of hypoxia-induced endothelial dysfunction. We hypothesized that acute hypoxia would have a deleterious effect on microvascular and large vessel endothelial function. Twenty-nine healthy adults [24 (SD = 4 ) years of age] completed normoxic and hypoxic [inspired O₂  fraction = 0.209] trials in this double-blinded, counterbalanced crossover study. After 30 min, we assessed the laser Doppler imaging-determined perfusion response to iontophoresis of ACh as a measure of endothelium-dependent microvascular function and iontophoresis of sodium nitroprusside as a measure of endothelium-independent microvascular function. After 60 min, we assessed brachial flow-mediated dilatation as a measure of large vessel endothelial function. Thirty minutes of hypoxia reduced endothelium-dependent microvascular function determined by the perfusion response to ACh (median difference (x̃∆) = -109% {interquartile range: 542.7}, P < 0.05), but not endothelium-independent microvascular function determined by the perfusion response to sodium nitroprusside (x̃∆ = 69% {interquartile range: 453.7}, P = 0.6). In addition, 60 min of hypoxia reduced allometrically scaled flow-mediated dilatation compared with normoxia ( x ¯ Δ = - 1.19 [95% CI = -1.80, -0.58 (Confidence Intervals)]%, P < 0.001). The decrease in microvascular endothelial function was associated with cardiorespiratory fitness (r  = 0.45, P = 0.02). In conclusion, acute exposure to normobaric hypoxia significantly reduced endothelium-dependent vasodilatory capacity in small and large vessels. Collectively, these findings highlight the sensitivity of the microvascular circulation to hypoxic insult, particularly in those with poor cardiorespiratory fitness.

Effects of Eight Weeks Altitude Training on the Aerobic Capacity and Microcirculation Function in Trained Rowers

Meng, Zhijun, Huan Gao, Tao Li, Peng Ge, Yixiao Xu, and Binghong Gao. Effects of eight weeks altitude training on the aerobic capacity and microcirculation function in trained rowers. High Alt Med Biol. 22:24-31, 2021. Background: The mechanism of aerobic improvement after altitude training (AT) has not been resolved yet. Few studies have looked at microcirculation changes after AT in athletes. Materials and Methods: Thirty-three male rowers were recruited and divided into either the AT (n = 18, altitude 2,280 m) or the sea level training (ST group, n = 15, altitude 50 m) for 8 weeks training. Microcirculation function was monitored using a laser Doppler flowmeter. VO_2peak and ergometer 5 km time trial (Er5k) were conducted. Results: Within the AT group there was an 8.8% increment in VO_2peak from pre- to post-training (4,708.9 ± 455.2 vs. 5,123.3 ± 391.2 ml/min, p < 0.01), whereas in ST group there was a 3.1% increase of VO_2peak from pre- to post-training (4,975.4 ± 501.1 vs. 5,128.0 ± 499.3 m/min, p = 0.125). Er5k performance in AT group was significantly improved (1,040.3 ± 26.3 vs. 1,033.2 ± 27.5 seconds, p = 0.038), whereas in ST group Er5k performance was not improved (1,059.6 ± 30.9 vs. 1,060.4 ± 33.2 seconds, p = 0.819). Postocclusive reactive hyperemia reserve and heat reserve in the forearm of AT subjects increased significantly after 8 weeks. Meanwhile, the AT group's resting blood flow and cutaneous vascular conductance (CVC) of the thigh were higher after AT. For the ST group, resting blood flow and CVC in the thigh decreased significantly at third week post-training. There was a low correlation between the change of VO_2peak and blood flow of the thigh (r = 0.45, p = 0.01). Conclusions: Trained rowers benefit more from 8 weeks of AT than from 8 weeks ST in terms of aerobic capacity. We have found that 8 weeks of AT increases thigh blood flow and improves endothelial function.

The nitric oxide dependence of cutaneous microvascular function to independent and combined hypoxic cold exposure

When separated from local cooling, whole body cooling elicited cutaneous reflex vasoconstriction via mechanisms independent of nitric oxide removal. Hypoxia elicited cutaneous vasodilatation via mechanisms mediated primarily by nitric oxide synthase, rather than xanthine oxidase-mediated nitrite reduction. Cold-induced vasoconstriction was blunted by the opposing effect of hypoxic vasodilatation, whereas the underpinning mechanisms did not interrelate in the absence of local cooling. Full vasoconstriction was restored with nitric oxide synthase inhibition.

Four weeks of hypoxia training improves cutaneous microcirculation in trained rowers

Hypoxia training can improve endurance performance. However, the specific benefits mechanism of hypoxia training is controversial, and there are just a few studies on the peripheral adaptation to hypoxia training. The main objective of this study was to observe the effects of hypoxia training on cutaneous blood flow (CBF), hypoxia-inducible factor (HIF), nitric oxide (NO), and vascular endothelial growth factor (VEGF). Twenty rowers were divided into two groups for four weeks of training, either hypoxia training (Living High, Exercise High and Training Low, HHL) or normoxia training (NOM). We tested cutaneous microcirculation by laser Doppler flowmeter and blood serum parameters by ELISA. HHL group improved the VO(2peak) and power at blood lactic acid of 4 mmol/l (P(4)) significantly. The CBF and the concentration of moving blood cells (CMBC) in the forearm of individuals in the HHL group increased significantly at the first week. The HIF level of the individuals in the HHL group increased at the fourth week. The NO of HHL group increased significantly at the fourth week. In collusion, four weeks of HHL training resulted in increased forearm cutaneous blood flow and transcutaneous oxygen pressure. HHL increases rowers' NO and VEGF, which may be the mechanism of increased blood flow. The increased of CBF seems to be related with improving performance.

Dietary nitrate supplementation increases acute mountain sickness severity and sense of effort during hypoxic exercise

Dietary nitrate supplementation enhances sea level performance and may ameliorate hypoxemia at high altitude. However, nitrate may exacerbate acute mountain sickness (AMS), specifically headache. This study investigated the effect of nitrate supplementation on AMS symptoms and exercise responses with 6-h hypoxia. Twenty recreationally active men [age, 22 ± 4 yr, maximal oxygen consumption (V̇o2max), 51 ± 6 ml·min−1·kg−1, means ± SD] completed this randomized double-blinded placebo-controlled crossover study. Twelve participants were classified as AMS− on the basis of Environmental Symptoms Questionnaire [Acute Cerebral Mountain Sickness score (AMS-C)] <0.7 in both trials, and five participants were classified as AMS+ on the basis of AMS-C ≥0.7 on placebo. Five days of nitrate supplementation (70-ml beetroot juice containing ~6.4 mmol nitrate daily) increased plasma NO metabolites by 182 µM compared with placebo but did not reduce AMS or improve exercise performance. After 4-h hypoxia [inspired O2 fraction ([Formula: see text]) = 0.124], nitrate increased AMS-C and headache severity (visual analog scale; whole sample ∆10 [1, 20] mm, mean difference [95% confidence interval]; P = 0.03) compared with placebo. In addition, after 5-h hypoxia, nitrate increased sense of effort during submaximal exercise (∆7 [−1, 14]; P = 0.07). In AMS−, nitrate did not alter headache or sense of effort. In contrast, in AMS+, nitrate increased headache severity (∆26 [−3, 56] mm; P = 0.07), sense of effort (∆14 [1, 28]; P = 0.04), oxygen consumption, ventilation, and mean arterial pressure during submaximal exercise. On the next day, in a separate acute hypoxic exercise test ([Formula: see text] = 0.141), nitrate did not improve time to exhaustion at 80% hypoxic V̇o2max. In conclusion, dietary nitrate increases AMS and sense of effort during exercise, particularly in those who experience AMS. Dietary nitrate is therefore not recommended as an AMS prophylactic or ergogenic aid in nonacclimatized individuals at altitude.

NEW & NOTEWORTHY This is the first study to identify that the popular dietary nitrate supplement (beetroot) does not reduce acute mountain sickness (AMS) or improve exercise performance during 6-h hypoxia. The consumption of nitrate in those susceptible to AMS exacerbates AMS symptoms (headache) and sense of effort and raises oxygen cost, ventilation, and blood pressure during walking exercise in 6-h hypoxia. These data question the suitability of nitrate supplementation during altitude travel in nonacclimatized people.

Thermoregulatory responses to exercise at a fixed rate of heat production are not altered by acute hypoxia

This study sought to assess the within-subject influence of acute hypoxia on exercise-induced changes in core temperature and sweating. Eight participants [1.75 (0.06) m, 70.2 (6.8) kg, 25 (4) yr, 54 (8) ml·kg^-1·min^-1] completed 45 min of cycling, once in normoxia (NORM; [Formula: see text] = 0.21) and twice in hypoxia (HYP1/HYP2; [Formula: see text]= 0.13) at 34.4(0.2)°C, 46(3)% RH. These trials were designed to elicit 1) two distinctly different %V̇o_2peak [NORM: 45 (8)% and HYP1: 62 (7)%] at the same heat production (H_prod) [NORM: 6.7 (0.6) W/kg and HYP1: 7.0 (0.5) W/kg]; and 2) the same %V̇o_2peak [NORM: 45 (8)% and HYP2: 48 (5)%] with different H_prod [NORM: 6.7 (0.6) W/kg and HYP2: 5.5 (0.6) W/kg]. At a fixed %V̇o_2peak, changes in rectal temperature (ΔT_re) and changes in esophageal temperature (ΔT_es) were greater at end-exercise in NORM [ΔT_re: 0.76 (0.19)°C; ΔT_es: 0.64 (0.22)°C] compared with HYP2 [ΔT_re: 0.56 (0.22)°C, P < 0.01; ΔT_es: 0.42 (0.21)°C, P < 0.01]. As a result of a greater H_prod (P < 0.01) in normoxia, and therefore evaporative heat balance requirements, to maintain a similar %V̇o_2peak compared with hypoxia, mean local sweat rates (LSR) from the forearm, upper back, and forehead were greater (all P < 0.01) in NORM [1.10 (0.20) mg·cm^-2·min^-1] compared with HYP2 [0.71 (0.19) mg·cm^-2·min^-1]. However, at a fixed H_prod, ΔT_re [0.75 (0.24)°C; P = 0.77] and ΔT_es [0.63 (0.29)°C; P = 0.69] were not different in HYP1, compared with NORM. Likewise, mean LSR [1.11 (0.20) mg·cm^-2·min^-1] was not different (P = 0.84) in HYP1 compared with NORM. These data demonstrate, using a within-subjects design, that hypoxia does not independently influence thermoregulatory responses. Additionally, further evidence is provided to support that metabolic heat production, irrespective of %V̇o_2peak, determines changes in core temperature and sweating during exercise.NEW & NOTEWORTHY Using a within-subject design, hypoxia does not independently alter core temperature and sweating during exercise at a fixed rate of heat production. These findings also further contribute to the development of a methodological framework for assessing differences in thermoregulatory responses to exercise between various populations and individuals. Using the combined environmental stressors of heat and hypoxia we conclusively demonstrate that exercise intensity relative to aerobic capacity (i.e., %V̇o_2max) does not influence changes in thermoregulatory responses.

Thermoregulatory responses to combined moderate heat stress and hypoxia

OBJECTIVE

The aim of this study was to examine the cutaneous vascular and sudomotor responses to combined moderate passive heat stress and normobaric hypoxia.

METHOD

Thirteen healthy young males, dressed in a water-perfused suit, underwent passive heating (Δcore temperature ~0.7°C) twice (Normoxia; 20.9% O₂ and Hypoxia; 13% O₂ ). Chest and forearm skin blood flow (SkBF; laser-Doppler flux) and sweat rate (SR; capacitance hygrometry), core (intestinal pill), and skin temperatures, were recorded.

RESULTS

Hypoxia reduced baseline oxygen saturation (98±1 vs 89±6%, P<.001) and elevated chest (P=.03) and forearm SkBF (P=.03), and HR (64±9 vs 69±8 beats.min^-1 , P<.01). During heating, mean body temperature (T¯BODY) thresholds for SkBF (P=.41) and SR (P=.28) elevations were not different between trials. The SkBF: T¯BODY linear sensitivity during the initial phase of heating was lower at the chest (P=.035) but not different at the forearm (P=.17) during hypoxia. With increasing levels of heating chest SkBF was not different (P=.55) but forearm SkBF was lower (P<.01) during hypoxia. Chest (P=.85) and forearm (P=.79) SR: T¯BODY linear sensitivities were not different between trials.

CONCLUSION

While sudomotor responses and the initiation of cutaneous blood flow elevations are unaffected, hypoxia differentially effects regional SkBF responses during moderate passive heating.

Unexpected reductions in regional cerebral perfusion during prolonged hypoxia

KEY POINTS

Cognitive performance is impaired by hypoxia despite global cerebral oxygen delivery and metabolism being maintained. Using arterial spin labelled (ASL) magnetic resonance imaging, this is the first study to show regional reductions in cerebral blood flow (CBF) in response to decreased oxygen supply (hypoxia) at 2 h that increased in area and became more pronounced at 10 h. Reductions in CBF were seen in brain regions typically associated with the 'default mode' or 'task negative' network. Regional reductions in CBF, and associated vasoconstriction, within the default mode network in hypoxia is supported by increased vasodilatation in these regions to a subsequent hypercapnic (5% CO₂ ) challenge. These results suggest an anatomical mechanism through which hypoxia may cause previously reported deficits in cognitive performance.

ABSTRACT

Hypoxia causes an increase in global cerebral blood flow, which maintains global cerebral oxygen delivery and metabolism. However, neurological deficits are abundant under hypoxic conditions. We investigated regional cerebral microvascular responses to acute (2 h) and prolonged (10 h) poikilocapnic normobaric hypoxia. We found that 2 h of hypoxia caused an expected increase in frontal cortical grey matter perfusion but unexpected perfusion decreases in regions of the brain normally associated with the 'default mode' or 'task negative' network. After 10 h in hypoxia, decreased blood flow to the major nodes of the default mode network became more pronounced and widespread. The use of a hypercapnic challenge (5% CO₂ ) confirmed that these reductions in cerebral blood flow from hypoxia were related to vasoconstriction. Our findings demonstrate steady-state deactivation of the default network under acute hypoxia, which become more pronounced over time. Moreover, these data provide a unique insight into the nuanced localized cerebrovascular response to hypoxia that is not attainable through traditional methods. The observation of reduced perfusion in the posterior cingulate and cuneal cortex, which are regions assumed to play a role in declarative and procedural memory, provides an anatomical mechanism through which hypoxia may cause deficits in working memory.

The contribution of sensory nerves to cutaneous vasodilatation of the forearm and leg to local skin heating

PURPOSE

The initial cutaneous vasodilatory response to local skin heating is larger in the forearm than the leg. While the initial vasodilatation of the forearm to local heating is primarily dependent on sensory nerves, their role in the leg is unknown. We compared the contribution of sensory nerves in driving the cutaneous vasodilatory response of the forearm and leg to local heating using local anaesthetic (EMLA) cream.

METHOD

In seven participants, two skin sites were selected on both the dorsal forearm and anterolateral calf; one site on each region received EMLA, with the other an untreated control. All sites were controlled at 33 °C and then locally heated to 42 °C with integrated laser-Doppler local heating probes.

RESULTS

Cutaneous vascular conductance (CVC) during the initial vasodilatation to local heating was smaller in the leg (47 ± 9% max) compared to the forearm (62 ± 7 % max) (P = 0.012). EMLA reduced the initial vasodilatation at both the leg (27 ± 13 % max) (P = 0.02) and forearm (33 ± 14% max) (P < 0.001). The times to onset of vasodilatation, initial vasodilatory peak, and plateau phase were longer in the leg compared to the forearm (all P < 0.05), and EMLA increased these times in both regions (both P < 0.05). CVC during the plateau phase to sustained local skin heating was higher in the leg compared to the forearm at both the untreated (93 ± 6 vs. 85 ± 4% max) (P = 0.33) and EMLA-treated (94 ± 5 vs. 86 ± 6% max) (P = 0.001) sites; EMLA did not affect CVC (P > 0.05).

CONCLUSION

The differences in the initial vasodilatory peak to local skin heating between the forearm and the leg are due to the contribution of sensory nerves.