scholarly journals Dehydration during whole‐body heat stress contributes to subsequent reductions in lower‐body negative pressure (LBNP) tolerance

2011 ◽  
Vol 25 (S1) ◽  
Author(s):  
Rebekah A. I. Lucas ◽  
Matthew S. Ganio ◽  
James Pearson ◽  
Craig G. Crandall
Keyword(s):  
Heat Stress ◽  
Negative Pressure ◽  
Lower Body Negative Pressure ◽  
Whole Body ◽  
Lower Body ◽  
Whole Body Heat Stress ◽  
Body Heat

scholarly journals Modelflow underestimates cardiac output in heat-stressed individuals

2011 ◽  
Vol 300 (2) ◽  
pp. R486-R491 ◽  
Author(s):  
Manabu Shibasaki ◽  
Thad E. Wilson ◽  
Morten Bundgaard-Nielsen ◽  
Thomas Seifert ◽  
Niels H. Secher ◽  
...  
Keyword(s):  
Cardiac Output ◽  
Heat Stress ◽  
Arterial Pressure ◽  
Lower Body Negative Pressure ◽  
Whole Body ◽  
Arterial Cannulation ◽  
Artery Cannulation ◽  
Whole Body Heat Stress ◽  
Acute Changes ◽  
Body Heat

An estimation of cardiac output can be obtained from arterial pressure waveforms using the Modelflow method. However, whether the assumptions associated with Modelflow calculations are accurate during whole body heating is unknown. This project tested the hypothesis that cardiac output obtained via Modelflow accurately tracks thermodilution-derived cardiac outputs during whole body heat stress. Acute changes of cardiac output were accomplished via lower-body negative pressure (LBNP) during normothermic and heat-stressed conditions. In nine healthy normotensive subjects, arterial pressure was measured via brachial artery cannulation and the volume-clamp method of the Finometer. Cardiac output was estimated from both pressure waveforms using the Modeflow method. In normothermic conditions, cardiac outputs estimated via Modelflow (arterial cannulation: 6.1 ± 1.0 l/min; Finometer 6.3 ± 1.3 l/min) were similar with cardiac outputs measured by thermodilution (6.4 ± 0.8 l/min). The subsequent reduction in cardiac output during LBNP was also similar among these methods. Whole body heat stress elevated internal temperature from 36.6 ± 0.3 to 37.8 ± 0.4°C and increased cardiac output from 6.4 ± 0.8 to 10.9 ± 2.0 l/min when evaluated with thermodilution ( P < 0.001). However, the increase in cardiac output estimated from the Modelflow method for both arterial cannulation (2.3 ± 1.1 l/min) and Finometer (1.5 ± 1.2 l/min) was attenuated compared with thermodilution (4.5 ± 1.4 l/min, both P < 0.01). Finally, the reduction in cardiac output during LBNP while heat stressed was significantly attenuated for both Modelflow methods (cannulation: −1.8 ± 1.2 l/min, Finometer: −1.5 ± 0.9 l/min) compared with thermodilution (−3.8 ± 1.19 l/min). These results demonstrate that the Modelflow method, regardless of Finometer or direct arterial waveforms, underestimates cardiac output during heat stress and during subsequent reductions in cardiac output via LBNP.

Divergent roles of plasma osmolality and the baroreflex on sweating and skin blood flow

2012 ◽  
Vol 302 (5) ◽  
pp. R634-R642 ◽  
Author(s):  
Aaron G. Lynn ◽  
Daniel Gagnon ◽  
Konrad Binder ◽  
Robert C. Boushel ◽  
Glen P. Kenny
Keyword(s):  
Blood Flow ◽  
Heat Stress ◽  
Core Temperature ◽  
Skin Blood Flow ◽  
Negative Pressure ◽  
Lower Body Negative Pressure ◽  
Plasma Osmolality ◽  
Whole Body ◽  
Lower Body ◽  
Change In Mean

Plasma hyperosmolality and baroreceptor unloading have been shown to independently influence the heat loss responses of sweating and cutaneous vasodilation. However, their combined effects remain unresolved. On four separate occasions, eight males were passively heated with a liquid-conditioned suit to 1.0°C above baseline core temperature during a resting isosmotic state (infusion of 0.9% NaCl saline) with (LBNP) and without (CON) application of lower-body negative pressure (−40 cmH2O) and during a hyperosmotic state (infusion of 3.0% NaCl saline) with (LBNP + HYP) and without (HYP) application of lower-body negative pressure. Forearm sweat rate (ventilated capsule) and skin blood flow (laser-Doppler), as well as core (esophageal) and mean skin temperatures, were measured continuously. Plasma osmolality increased by ∼10 mosmol/kgH2O during HYP and HYP + LBNP conditions, whereas it remained unchanged during CON and LBNP ( P ≤ 0.05). The change in mean body temperature (0.8 × core temperature + 0.2 × mean skin temperature) at the onset threshold for increases in cutaneous vascular conductance (CVC) was significantly greater during LBNP (0.56 ± 0.24°C) and HYP (0.69 ± 0.36°C) conditions compared with CON (0.28 ± 0.23°C, P ≤ 0.05). Additionally, the onset threshold for CVC during LBNP + HYP (0.88 ± 0.33°C) was significantly greater than CON and LBNP conditions ( P ≤ 0.05). In contrast, onset thresholds for sweating were not different during LBNP (0.50 ± 0.18°C) compared with CON (0.46 ± 0.26°C, P = 0.950) but were elevated ( P ≤ 0.05) similarly during HYP (0.91 ± 0.37°C) and LBNP + HYP (0.94 ± 0.40°C). Our findings show an additive effect of hyperosmolality and baroreceptor unloading on the onset threshold for increases in CVC during whole body heat stress. In contrast, the onset threshold for sweating during heat stress was only elevated by hyperosmolality with no effect of the baroreflex.

scholarly journals Heat Stress and Cardiovascular, Hormonal, and Heat Shock Proteins in Humans

2012 ◽  
Vol 47 (2) ◽  
pp. 184-190 ◽  
Author(s):  
Masaki Iguchi ◽  
Andrew E. Littmann ◽  
Shuo-Hsiu Chang ◽  
Lydia A. Wester ◽  
Jane S. Knipper ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Heat Stress ◽  
Heat Shock ◽  
Body Temperature ◽  
Controlled Trial ◽  
Whole Body ◽  
Cord Injury ◽  
Whole Body Heat Stress ◽  
Body Heat

Context: Conditions such as osteoarthritis, obesity, and spinal cord injury limit the ability of patients to exercise, preventing them from experiencing many well-documented physiologic stressors. Recent evidence indicates that some of these stressors might derive from exercise-induced body temperature increases. Objective: To determine whether whole-body heat stress without exercise triggers cardiovascular, hormonal, and extra-cellular protein responses of exercise. Design: Randomized controlled trial. Setting: University research laboratory. Patients or Other Participants: Twenty-five young, healthy adults (13 men, 12 women; age = 22.1 ± 2.4 years, height = 175.2 ± 11.6 cm, mass = 69.4 ± 14.8 kg, body mass index = 22.6 ± 4.0) volunteered. Intervention(s): Participants sat in a heat stress chamber with heat (73°C) and without heat (26°C) stress for 30 minutes on separate days. We obtained blood samples from a subset of 13 participants (7 men, 6 women) before and after exposure to heat stress. Main Outcome Measure(s): Extracellular heat shock protein (HSP72) and catecholamine plasma concentration, heart rate, blood pressure, and heat perception. Results: After 30 minutes of heat stress, body temperature measured via rectal sensor increased by 0.8°C. Heart rate increased linearly to 131.4 ± 22.4 beats per minute (F6,24 = 186, P &lt; .001) and systolic and diastolic blood pressure decreased by 16 mm Hg (F6,24 = 10.1, P &lt; .001) and 5 mm Hg (F6,24 = 5.4, P &lt; .001), respectively. Norepinephrine (F1,12 = 12.1, P = .004) and prolactin (F1,12 = 30.2, P &lt; .001) increased in the plasma (58% and 285%, respectively) (P &lt; .05). The HSP72 (F1,12 = 44.7, P &lt; .001) level increased with heat stress by 48.7% ± 53.9%. No cardiovascular or blood variables showed changes during the control trials (quiet sitting in the heat chamber with no heat stress), resulting in differences between heat and control trials. Conclusions: We found that whole-body heat stress triggers some of the physiologic responses observed with exercise. Future studies are necessary to investigate whether carefully prescribed heat stress constitutes a method to augment or supplement exercise.

scholarly journals Carotid baroreflex control of heart rate is enhanced during whole‐body heat stress

2013 ◽  
Vol 27 (S1) ◽  
Author(s):  
Davor Krnjajic ◽  
Cory L Butts ◽  
W Shane Warren ◽  
Mitchel R Samels ◽  
David M Keller
Keyword(s):  
Heart Rate ◽  
Heat Stress ◽  
Whole Body ◽  
Baroreflex Control ◽  
Carotid Baroreflex ◽  
Whole Body Heat Stress ◽  
Body Heat

scholarly journals Roles of nitric oxide synthase isoforms in cutaneous vasodilation induced by local warming of the skin and whole body heat stress in humans

2009 ◽  
Vol 107 (5) ◽  
pp. 1438-1444 ◽  
Author(s):  
Dean L. Kellogg ◽  
Joan L. Zhao ◽  
Yubo Wu
Keyword(s):  
Nitric Oxide ◽  
Heat Stress ◽  
No Synthase ◽  
Whole Body ◽  
Doppler Flowmetry ◽  
Vasodilator Response ◽  
Cutaneous Vasodilation ◽  
Forearm Skin ◽  
Whole Body Heat Stress ◽  
Body Heat

Nitric oxide (NO) participates in the cutaneous vasodilation caused by increased local skin temperature (Tloc) and whole body heat stress in humans. In forearm skin, endothelial NO synthase (eNOS) participates in vasodilation due to elevated Tloc and neuronal NO synthase (nNOS) participates in vasodilation due to heat stress. To explore the relative roles and interactions of these isoforms, we examined the effects of a relatively specific eNOS inhibitor, Nω-amino-l-arginine (LNAA), and a specific nNOS inhibitor, Nω-propyl-l-arginine (NPLA), both separately and in combination, on skin blood flow (SkBF) responses to increased Tloc and heat stress in two protocols. In each protocol, SkBF was monitored by laser-Doppler flowmetry (LDF) and mean arterial pressure (MAP) by Finapres. Cutaneous vascular conductance (CVC) was calculated (CVC = LDF/MAP). Intradermal microdialysis was used to treat one site with 5 mM LNAA, another with 5 mM NPLA, a third with combined 5 mM LNAA and 5 mM NPLA (Mix), and a fourth site with Ringer only. In protocol 1, Tloc was controlled with combined LDF/local heating units. Tloc was increased from 34°C to 41.5°C to cause local vasodilation. In protocol 2, after a period of normothermia, whole body heat stress was induced (water-perfused suits). At the end of each protocol, all sites were perfused with 58 mM nitroprusside to effect maximal vasodilation for data normalization. In protocol 1, at Tloc = 34°C, CVC did not differ between sites ( P > 0.05). LNAA and Mix attenuated CVC increases at Tloc = 41.5°C to similar extents ( P < 0.05, LNAA or Mix vs. untreated or NPLA). In protocol 2, in normothermia, CVC did not differ between sites ( P > 0.05). During heat stress, NPLA and Mix attenuated CVC increases to similar extents, but no significant attenuation occurred with LNAA ( P < 0.05, NPLA or Mix vs. untreated or LNAA). In forearm skin, eNOS mediates the vasodilator response to increased Tloc and nNOS mediates the vasodilator response to heat stress. The two isoforms do not appear to interact during either response.

Whole body heat stress fails to limit infarct size in the reperfused rabbit heart

1992 ◽  
Vol 26 (4) ◽  
pp. 342-346 ◽  
Author(s):  
D. M Yellon ◽  
E. Iliodromitis ◽  
D. S Latchman ◽  
D. M V. Winkle ◽  
J. M Downey ◽  
...  
Keyword(s):  
Heat Stress ◽  
Infarct Size ◽  
Rabbit Heart ◽  
Whole Body ◽  
Whole Body Heat Stress ◽  
Body Heat

scholarly journals Carotid baroreflex control of heart rate is enhanced, while control of mean arterial pressure is preserved during whole body heat stress in young healthy men

2016 ◽  
Vol 311 (4) ◽  
pp. R735-R741 ◽  
Author(s):  
Davor Krnjajic ◽  
Dustin R. Allen ◽  
Cory L. Butts ◽  
David M. Keller
Keyword(s):  
Heart Rate ◽  
Heat Stress ◽  
Mean Arterial Pressure ◽  
Arterial Pressure ◽  
Whole Body ◽  
Chamber Pressure ◽  
Carotid Baroreflex ◽  
Whole Body Heat Stress ◽  
Neck Pressure ◽  
Body Heat

Whole body heat stress (WBH) results in numerous cardiovascular alterations that ultimately reduce orthostatic tolerance. While impaired carotid baroreflex (CBR) function during WBH has been reported as a potential reason for this decrement, study design considerations may limit interpretation of previous findings. We sought to test the hypothesis that CBR function is unaltered during WBH. CBR function was assessed in 10 healthy male subjects (age: 26 ± 3; height: 185 ± 7 cm; weight: 82 ± 10 kg; BMI: 24 ± 3 kg/m2; means ± SD) using 5-s trials of neck pressure (+45, +30, and +15 Torr) and neck suction (−20, −40, −60, and −80 Torr) during normothermia (NT) and passive WBH (Δ core temp ∼1°C). Analyses of stimulus response curves (four-parameter logistic model) for CBR control of heart rate (CBR-HR) and mean arterial pressure (CBR-MAP), as well as separate two-way ANOVA of the hypotensive and hypertensive stimuli (factor 1: thermal condition, factor 2: chamber pressure), were performed. For CBR-HR, maximal gain was increased during WBH (−0.73 ± 0.11) compared with NT (−0.39 ± 0.04, mean ± SE, P = 0.03). In addition, the CBR-HR responding range was increased during WBH (33 ± 5) compared with NT (19 ± 2 bpm, P = 0.03). Separate analysis of hypertensive stimulation revealed enhanced HR responses during WBH at −40, −60, and −80 Torr (condition × chamber pressure interaction, P = 0.049) compared with NT. For CBR-MAP, both logistic analysis and separate two-way ANOVA revealed no differences during WBH. Therefore, in response to passive WBH, CBR control of heart rate (enhanced) and arterial pressure (no change) is well preserved.

scholarly journals Sweat loss during heat stress contributes to subsequent reductions in lower-body negative pressure tolerance

2012 ◽  
Vol 98 (2) ◽  
pp. 473-480 ◽  
Author(s):  
Rebekah A. I. Lucas ◽  
Matthew S. Ganio ◽  
James Pearson ◽  
Craig G. Crandall
Keyword(s):  
Heat Stress ◽  
Negative Pressure ◽  
Lower Body Negative Pressure ◽  
Lower Body ◽  
Sweat Loss ◽  
Pressure Tolerance

scholarly journals Endothelial nitric oxide synthase control mechanisms in the cutaneous vasculature of humans in vivo

2008 ◽  
Vol 295 (1) ◽  
pp. H123-H129 ◽  
Author(s):  
Dean L. Kellogg ◽  
Joan L. Zhao ◽  
Yubo Wu
Keyword(s):  
Nitric Oxide ◽  
Heat Stress ◽  
Local Heating ◽  
Ringer Solution ◽  
Whole Body ◽  
Control Mechanisms ◽  
Local Skin ◽  
Doppler Flowmetry ◽  
Whole Body Heat Stress ◽  
Body Heat

Nitric oxide (NO) participates in locally mediated vasodilation induced by increased local skin temperature (Tloc) and in sympathetically mediated vasodilation during whole body heat stress. We hypothesized that endothelial NOS (eNOS) participates in the former, but not the latter, response. We tested this hypothesis by examining the effects of the eNOS antagonist NG-amino-l-arginine (l-NAA) on skin blood flow (SkBF) responses to increased Tloc and whole body heat stress. Microdialysis probes were inserted into forearm skin for drug delivery. One microdialysis site was perfused with l-NAA in Ringer solution and a second site with Ringer solution alone. SkBF [laser-Doppler flowmetry (LDF)] and blood pressure [mean arterial pressure (MAP)] were monitored, and cutaneous vascular conductance (CVC) was calculated (CVC = LDF ÷ MAP). In protocol 1, Tloc was controlled with LDF/local heating units. Tloc initially was held at 34°C and then increased to 41.5°C. In protocol 2, after a normothermic period, whole body heat stress was induced (water-perfused suits). At the end of both protocols, 58 mM sodium nitroprusside was perfused at both microdialysis sites to cause maximal vasodilation for data normalization. In protocol 1, CVC at 34°C Tloc did not differ between l-NAA-treated and untreated sites ( P > 0.05). Local skin warming to 41.5°C Tloc increased CVC at both sites. This response was attenuated at l-NAA-treated sites ( P < 0.05). In protocol 2, during normothermia, CVC did not differ between l-NAA-treated and untreated sites ( P > 0.05). During heat stress, CVC rose to similar levels at l-NAA-treated and untreated sites ( P > 0.05). We conclude that eNOS is predominantly responsible for NO generation in skin during responses to increased Tloc, but not during reflex responses to whole body heat stress.

scholarly journals Tissue Doppler indices of cardiac contractile function during whole‐body heat stress

2008 ◽  
Vol 22 (S1) ◽  
Author(s):  
R Matthew Brothers ◽  
Paul S. Bhella ◽  
Shigeki Shibata ◽  
Jonathan E. Wingo ◽  
Benjamin D. Levine ◽  
...  
Keyword(s):  
Heat Stress ◽  
Contractile Function ◽  
Tissue Doppler ◽  
Whole Body ◽  
Cardiac Contractile Function ◽  
Cardiac Contractile ◽  
Whole Body Heat Stress ◽  
Doppler Indices ◽  
Body Heat
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