scholarly journals Sustained increases in skin blood flow are not a prerequisite to initiate sweating during passive heat exposure

2017 ◽  
Vol 313 (2) ◽  
pp. R140-R148 ◽  
Author(s):  
Nicholas Ravanelli ◽  
Ollie Jay ◽  
Daniel Gagnon
Keyword(s):  
Blood Flow ◽  
Vapor Pressure ◽  
Skin Blood Flow ◽  
Sweat Rate ◽  
Heat Exposure ◽  
Mean Body Temperature ◽  
Local Skin ◽  
Sweat Production ◽  
Sweating Efficiency ◽  
Change In Mean

Some studies have observed a functional relationship between sweating and skin blood flow. However, the implications of this relationship during physiologically relevant conditions remain unclear. We manipulated sudomotor activity through changes in sweating efficiency to determine if parallel changes in vasomotor activity are observed. Eight young men completed two trials at 36°C and two trials at 42°C. During these trials, air temperature remained constant while ambient vapor pressure increased from 1.6 to 5.6 kPa over 2 h. Forced airflow across the skin was used to create conditions of high (HiSeff) or low (LoSeff) sweating efficiency. Local sweat rate (LSR), local skin blood flow (SkBF), as well as mean skin and esophageal temperatures were measured continuously. It took longer for LSR to increase during HiSeff at 36°C (HiSeff: 99 ± 11 vs. LoSeff: 77 ± 11 min, P < 0.01) and 42°C (HiSeff: 72 ± 16 vs. LoSeff: 51 ± 15 min, P < 0.01). In general, an increase in LSR preceded the increase in SkBF when expressed as ambient vapor pressure and time for all conditions ( P < 0.05). However, both responses were activated at a similar change in mean body temperature (average across all trials, LSR: 0.26 ± 0.15 vs. SkBF: 0.30 ± 0.18°C, P = 0.26). These results demonstrate that altering the point at which LSR is initiated during heat exposure is paralleled by similar shifts for the increase in SkBF. However, local sweat production occurs before an increase in SkBF, suggesting that SkBF is not necessarily a prerequisite for sweating.

scholarly journals Skin blood flow and local temperature independently modify sweat rate during passive heat stress in humans

2010 ◽  
Vol 109 (5) ◽  
pp. 1301-1306 ◽  
Author(s):  
Jonathan E. Wingo ◽  
David A. Low ◽  
David M. Keller ◽  
R. Matthew Brothers ◽  
Manabu Shibasaki ◽  
...  
Keyword(s):  
Blood Flow ◽  
Body Temperature ◽  
Skin Blood Flow ◽  
Sweat Rate ◽  
Local Temperature ◽  
Whole Body ◽  
Local Cooling ◽  
Mean Body Temperature ◽  
Local Skin ◽  
Doppler Flowmetry

Sweat rate (SR) is reduced in locally cooled skin, which may result from decreased temperature and/or parallel reductions in skin blood flow. The purpose of this study was to test the hypotheses that decreased skin blood flow and decreased local temperature each independently attenuate sweating. In protocols I and II, eight subjects rested supine while wearing a water-perfused suit for the control of whole body skin and internal temperatures. While 34°C water perfused the suit, four microdialysis membranes were placed in posterior forearm skin not covered by the suit to manipulate skin blood flow using vasoactive agents. Each site was instrumented for control of local temperature and measurement of local SR (capacitance hygrometry) and skin blood flow (laser-Doppler flowmetry). In protocol I, two sites received norepinephrine to reduce skin blood flow, while two sites received Ringer solution (control). All sites were maintained at 34°C. In protocol II, all sites received 28 mM sodium nitroprusside to equalize skin blood flow between sites before local cooling to 20°C (2 sites) or maintenance at 34°C (2 sites). In both protocols, individuals were then passively heated to increase core temperature ∼1°C. Both decreased skin blood flow and decreased local temperature attenuated the slope of the SR to mean body temperature relationship (2.0 ± 1.2 vs. 1.0 ± 0.7 mg·cm−2·min−1·°C−1 for the effect of decreased skin blood flow, P = 0.01; 1.2 ± 0.9 vs. 0.07 ± 0.05 mg·cm−2·min−1·°C−1 for the effect of decreased local temperature, P = 0.02). Furthermore, local cooling delayed the onset of sweating (mean body temperature of 37.5 ± 0.4 vs. 37.6 ± 0.4°C, P = 0.03). These data demonstrate that local cooling attenuates sweating by independent effects of decreased skin blood flow and decreased local skin temperature.

Active cutaneous vasodilation in resting humans during mild heat stress

2005 ◽  
Vol 98 (3) ◽  
pp. 829-837 ◽  
Author(s):  
Yoshi-Ichiro Kamijo ◽  
Kichang Lee ◽  
Gary W. Mack
Keyword(s):  
Blood Flow ◽  
Heat Stress ◽  
Skin Temperature ◽  
Skin Blood Flow ◽  
Sweat Rate ◽  
Mean Skin Temperature ◽  
Local Skin ◽  
Mild Heat ◽  
Normal Core ◽  
Local Sweat Rate

The role of skin temperature in reflex control of the active cutaneous vasodilator system was examined in six subjects during mild graded heat stress imposed by perfusing water at 34, 36, 38, and 40°C through a tube-lined garment. Skin sympathetic nerve activity (SSNA) was recorded from the peroneal nerve with microneurography. While monitoring esophageal, mean skin, and local skin temperatures, we recorded skin blood flow at bretylium-treated and untreated skin sites by using laser-Doppler velocimetry and local sweat rate by using capacitance hygrometry on the dorsal foot. Cutaneous vascular conductance (CVC) was calculated by dividing skin blood flow by mean arterial pressure. Mild heat stress increased mean skin temperature by 0.2 or 0.3°C every stage, but esophageal and local skin temperature did not change during the first three stages. CVC at the bretylium tosylate-treated site (CVCBT) and sweat expulsion number increased at 38 and 40°C compared with 34°C ( P < 0.05); however, CVC at the untreated site did not change. SSNA increased at 40°C ( P < 0.05, different from 34°C). However, SSNA burst amplitude increased ( P < 0.05), whereas SSNA burst duration decreased ( P < 0.05), at the same time as we observed the increase in CVCBT and sweat expulsion number. These data support the hypothesis that the active vasodilator system is activated by changes in mean skin temperature, even at normal core temperature, and illustrate the intricate competition between active vasodilator and the vasoconstrictor system for control of skin blood flow during mild heat stress.

scholarly journals Does attenuated skin blood flow lower sweat rate and the critical environmental limit for heat balance during severe heat exposure?

2016 ◽  
Vol 102 (2) ◽  
pp. 202-213 ◽  
Author(s):  
Matthew N. Cramer ◽  
Daniel Gagnon ◽  
Craig G. Crandall ◽  
Ollie Jay
Keyword(s):  
Blood Flow ◽  
Skin Blood Flow ◽  
Heat Balance ◽  
Sweat Rate ◽  
Heat Exposure

scholarly journals Effects of mode of exercise recovery on thermoregulatory and cardiovascular responses

2002 ◽  
Vol 93 (6) ◽  
pp. 1918-1924 ◽  
Author(s):  
Robert Carter ◽  
Thad E. Wilson ◽  
Donald E. Watenpaugh ◽  
Michael L. Smith ◽  
Craig G. Crandall
Keyword(s):  
Blood Flow ◽  
Skin Blood Flow ◽  
Heat Dissipation ◽  
Sweat Rate ◽  
Local Heating ◽  
Cardiovascular Responses ◽  
Maximal Heart Rate ◽  
Exercise Recovery ◽  
Active Recovery ◽  
Arterial Blood

To identify the effects of exercise recovery mode on cutaneous vascular conductance (CVC) and sweat rate, eight healthy adults performed two 15-min bouts of upright cycle ergometry at 60% of maximal heart rate followed by either inactive or active (loadless pedaling) recovery. An index of CVC was calculated from the ratio of laser-Doppler flux to mean arterial pressure. CVC was then expressed as a percentage of maximum (%max) as determined from local heating. At 3 min postexercise, CVC was greater during active recovery (chest: 40 ± 3, forearm: 48 ± 3%max) compared with during inactive recovery (chest: 21 ± 2, forearm: 25 ± 4%max); all P < 0.05. Moreover, at the same time point sweat rate was greater during active recovery (chest: 0.47 ± 0.10, forearm: 0.46 ± 0.10 mg · cm−2 · min−1) compared with during inactive recovery (chest: 0.28 ± 0.10, forearm: 0.14 ± 0.20 mg · cm−2 · min−1); all P < 0.05. Mean arterial blood pressure, esophageal temperature, and skin temperature were not different between recovery modes. These data suggest that skin blood flow and sweat rate during recovery from exercise may be modulated by nonthermoregulatory mechanisms and that sustained elevations in skin blood flow and sweat rate during mild active recovery may be important for postexertional heat dissipation.

scholarly journals Effect of local skin blood flow during light and medium activities on local skin temperature predictions

2019 ◽  
Vol 84 ◽  
pp. 439-450
Author(s):  
Stephanie Veselá ◽  
Boris R.M. Kingma ◽  
Arjan J.H. Frijns ◽  
Wouter D. van Marken Lichtenbelt
Keyword(s):  
Blood Flow ◽  
Skin Temperature ◽  
Skin Blood Flow ◽  
Local Skin ◽  
Local Skin Temperature

A synthetic undergarment increases physiological strain

2019 ◽  
Vol 28 (4) ◽  
pp. 275 ◽  
Author(s):  
Matthew C. Dorton ◽  
Brent C. Ruby ◽  
Charles L. Dumke
Keyword(s):  
Blood Flow ◽  
Skin Blood Flow ◽  
Perceived Exertion ◽  
Sweat Rate ◽  
Rest Period ◽  
Time Trial ◽  
Rating Of Perceived Exertion ◽  
Physiological Strain ◽  
Physiological Factors ◽  
Increased Risk

Our aim was to examine the effect of a synthetic material undergarment on heat stress during exercise in a hot environment. Ten active males completed two trials of intermittent (50min walking, 10min sitting) treadmill walking over 3h in 35°C and 30% relative humidity. Subjects wore wildland firefighter flame-resistant meta-aramid blend pants and shirt with either a 100% cotton (C) or flame-retardant modacrylic undergarment (S), while carrying a 16-kg pack, helmet and leather gloves. Exercise was followed by a 30-min rest period without pack, helmet, gloves, and outerwear shirt. Rectal temperature and physiological strain were greater in S than C (P=0.04). No significant differences were found for heart rate, rating of perceived exertion, energy expenditure or skin temperature between C and S. Skin blood flow increased significantly in S following the second hour of exercise, resulting in a time×trial interaction (P=0.001). No significant differences for skin blood flow were found post exercise. Sweat rate and percent dehydration were not different between C and S. These data indicate that, of the two undergarments investigated, the synthetic undergarment negatively affected physiological factors that have been shown to indicate an increased risk of heat-related injuries.

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

2010 ◽  
Vol 109 (4) ◽  
pp. 1221-1228 ◽  
Author(s):  
Nisha Charkoudian
Keyword(s):  
Blood Flow ◽  
Human Skin ◽  
Skin Blood Flow ◽  
Cold Exposure ◽  
Heat Dissipation ◽  
Sympathetic Innervation ◽  
Heat Exposure ◽  
Reproductive Hormones ◽  
Excessive Heat ◽  
Cutaneous Vasodilation

Human skin blood flow responses to body heating and cooling are essential to the normal processes of physiological thermoregulation. Large increases in skin blood flow provide the necessary augmentation of convective heat loss during environmental heat exposure and/or exercise, just as reflex cutaneous vasoconstriction is key to preventing excessive heat dissipation during cold exposure. In humans, reflex sympathetic innervation of the cutaneous circulation has two branches: a sympathetic noradrenergic vasoconstrictor system, and a non-noradrenergic active vasodilator system. Noradrenergic vasoconstrictor nerves are tonically active in normothermic environments and increase their activity during cold exposure, releasing both norepinephrine and cotransmitters (including neuropeptide Y) to decrease skin blood flow. The active vasodilator system in human skin does not exhibit resting tone and is only activated during increases in body temperature, such as those brought about by heat exposure or exercise. Active cutaneous vasodilation occurs via cholinergic nerve cotransmission and has been shown to include potential roles for nitric oxide, vasoactive intestinal peptide, prostaglandins, and substance P (and/or neurokinin-1 receptors). It has proven both interesting and challenging that no one substance has been identified as the sole mediator of active cutaneous vasodilation. The processes of reflex cutaneous vasodilation and vasoconstriction are both modified by acute factors, such as exercise and hydration, and more long-term factors, such as aging, reproductive hormones, and disease. This review will highlight some of the recent findings in these areas, as well as interesting areas of ongoing and future work.

Control of skin blood flow by whole body and local skin cooling in exercising humans

1996 ◽  
Vol 270 (1) ◽  
pp. H208-H215 ◽  
Author(s):  
P. E. Pergola ◽  
J. M. Johnson ◽  
D. L. Kellogg ◽  
W. A. Kosiba
Keyword(s):  
Blood Flow ◽  
Skin Blood Flow ◽  
Threshold Level ◽  
Tissue Temperature ◽  
Whole Body ◽  
Internal Temperature ◽  
Local Cooling ◽  
Local Skin ◽  
Doppler Flowmetry ◽  
Rate Of Increase

We examined the independent roles of whole body skin temperature (Tsk) and tissue temperature (local temperature, Tloc) in the control of skin blood flow (SBF) during cooling and the roles of the vasoconstrictor (VC) and active vasodilator (AVD) systems in mediating these effects. SBF was monitored by laser-Doppler flowmetry (LDF) at untreated sites and sites with local VC blockade by pretreatment with bretylium (BT). Seven subjects underwent four sessions of moderate bicycle exercise (20-30 min duration) at neutral Tsk and Tloc (34 degrees C), neutral Tsk and cool Tloc (27 degrees C), low Tsk (28 degrees C) and neutral Tloc, and low Tsk and Tloc. Cutaneous vascular conductance (CVC; LDF/mean arterial pressure) was expressed relative to the maximum. Cool Tsk increased the threshold level of internal temperature at which CVC began to rise equally at BT-treated and untreated sites (P < 0.05). The rate of increase in CVC relative to internal temperature was reduced by local cooling. BT pretreatment partially reversed this effect (P < 0.05). Thus a cool environment results in reflex inhibition of the onset of AVD activity by cool Tsk and a reduced rate of increase in CVC due, in part, to norepinephrine release stimulated by cool Tloc.

Mechanisms of control of skin blood flow during prolonged exercise in humans

1993 ◽  
Vol 265 (2) ◽  
pp. H562-H568 ◽  
Author(s):  
D. L. Kellogg ◽  
J. M. Johnson ◽  
W. L. Kenney ◽  
P. E. Pergola ◽  
W. A. Kosiba
Keyword(s):  
Blood Flow ◽  
Skin Blood Flow ◽  
Sweat Rate ◽  
Bicycle Ergometer ◽  
Dew Point ◽  
Whole Body ◽  
Internal Temperature ◽  
Vasodilator Activity ◽  
Forearm Skin ◽  
Reduced Rate

Exercise in a warm environment raises internal temperature and leads to a rapid increase in skin blood flow (SkBF). As exercise continues, and internal temperature approaches 38 degrees C, the rate of rise of SkBF is markedly attenuated despite further significant increases in internal temperature. To find whether this attenuation is mediated by increased cutaneous active vasoconstrictor activity or by a reduced rate of rise of active vasodilator activity, each of 12 male subjects had 0.64 cm2 forearm skin sites iontophoretically treated with bretylium tosylate for selective local blockade of noradrenergic vasoconstrictor nerves. SkBF was monitored there and at adjacent untreated control sites by laser-Doppler blood flowmetry (LDF). Whole body skin temperature (Tsk) was controlled by water-perfused suits, and esophageal temperature (Tes) was monitored as an index of internal temperature. Mean arterial pressure (MAP) was monitored and cutaneous vascular conductance was calculated as LDF/MAP. Sweat rate was also monitored by dew point hygrometry in 11 subjects. Tsk was raised to 38 degrees C, after which subjects began 20-30 min of exercise on a bicycle ergometer. The rate of the initial rapid increase in SkBF with increasing Tes was not altered by bretylium treatment (P > 0.05 between sites). The attenuation of the rate of rise during the latter phase of exercise was not abolished by bretylium treatment (P > 0.05 between sites); instead, there was a trend for the attenuation to be enhanced at those sites. We conclude that the attenuated rate of rise of SkBF is due to limitation of active vasodilator activity and not due to increased vasoconstrictor tone.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Temperature of water ingested before exercise alters the onset of physiological heat loss responses

2019 ◽  
Vol 316 (1) ◽  
pp. R13-R20 ◽  
Author(s):  
Nathan B. Morris ◽  
Georgia K. Chaseling ◽  
Anthony R. Bain ◽  
Ollie Jay
Keyword(s):  
Blood Pressure ◽  
Blood Flow ◽  
Body Temperature ◽  
Relative Humidity ◽  
Body Mass ◽  
Sweat Rate ◽  
Vascular Conductance ◽  
Mean Body Temperature ◽  
Local Sweat Rate ◽  
Cutaneous Vascular Conductance

This study sought to determine whether the temperature of water ingested before exercise alters the onset threshold and subsequent thermosensitivity of local vasomotor and sudomotor responses after exercise begins. Twenty men [24 (SD 4) yr of age, 75.8 (SD 8.1) kg body mass, 52.3 (SD 7.7) ml·min−1·kg−1peak O2consumption (V̇o2peak)] ingested 1.5°C, 37°C, or 50°C water (3.2 ml/kg), rested for 5 min, and then cycled at 50% V̇o2peakfor 15 min at 23.0 (SD 0.9) °C and 32 (SD 10) % relative humidity. Mean body temperature (Tb), local sweat rate (LSR), and skin blood flow (SBF) were measured. In a subset of eight men [25 (SD 5) yr of age, 78.6 (SD 8.3) kg body mass, 48.9 (SD 11.1) ml·min−1·kg−1V̇o2peak], blood pressure was measured and cutaneous vascular conductance (CVC) was determined. The change in Tbwas greater at the onset of LSR measurement with ingestion of 1.5°C than 50°C water [ΔTb= 0.19 (SD 0.15) vs. 0.11 (SD 0.12) °C, P = 0.04], but not 37°C water [ΔTb= 0.14 (SD 0.14) °C, P = 0.23], but did not differ between trials for SBF measurement [ΔTb= 0.18 (SD 0.15) °C, 0.11 (SD 0.13) °C, and 0.09 (SD 0.09) °C with 1.5°C, 37°C, and 50°C water, respectively, P = 0.07]. Conversely, the thermosensitivity of LSR and SBF was not different [LSR = 1.11 (SD 0.75), 1.11 (SD 0.75), and 1.34 (SD 1.11) mg·min−1·cm−2·°C−1with 1.5°C, 37°C, and 50°C ingested water, respectively ( P = 0.46); SBF = 717 (SD 882), 517 (SD 606), and 857 (SD 904) %baseline arbitrary units (AU)/°C with 1.5°C, 37°C, and 50°C ingested water, respectively ( P = 0.95)]. After 15 min of exercise, LSR and SBF were greater with ingestion of 50°C than 1.5°C water [LSR = 0.40 (SD 0.17) vs. 0.31 (SD 0.19) mg·min−1·cm−2( P = 0.02); SBF = 407 (SD 149) vs. 279 (SD 117) %baseline AU ( P < 0.001)], but not 37°C water [LSR = 0.50 (SD 0.22) mg·min−1·cm−2; SBF = 324 (SD 169) %baseline AU]. CVC was statistically unaffected [275 (SD 81), 340 (SD 114), and 384 (SD 160) %baseline CVC with 1.5°C, 37°C, and 50°C ingested water, respectively, P = 0.30]. Collectively, these results support the concept that visceral thermoreceptors modify the central drive for thermoeffector responses.

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