Effect of heat stress on muscle sympathetic nerve activity in humans

Niimi, Yoshiji; Matsukawa, Tetsuya; Sugiyama, Yoshiki; Shamsuzzaman, Abu; Itô, Haruo; Sobue, Gen; Mano, Tadaaki

doi:10.1016/s0165-1838(96)00134-8

Cited by 95 publications

(95 citation statements)

References 13 publications

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“…Similar to previous studies (3,19), in the present study, MSNA increased significantly during heat stress. This observation, coupled with a lack of change in the gain of the relationship between diastolic blood pressure and MSNA, suggests whole body heating caused an upward shift of the baroreflex curve governing MSNA (Table 1).…”

Section: Discussionsupporting

confidence: 93%

Baroreflex modulation of sympathetic nerve activity to muscle in heat-stressed humans

Cui

Wilson

Crandall

2002

American Journal of Physiology-Regulatory, Integrative and Comp

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Baroreflex modulation of sympathetic nerve activity to muscle in heat-stressed humans. Am J Physiol Regulatory Integrative Comp Physiol 282: R252-R258, 2002; 10.1152/ajpregu. 00337.2001.-To identify whether whole body heating alters arterial baroreflex control of muscle sympathetic nerve activity (MSNA), MSNA and beat-by-beat arterial blood pressure were recorded in seven healthy subjects during acute hypotensive and hypertensive stimuli in both normothermic and heat stress conditions. Whole body heating significantly increased sublingual temperature (P Ͻ 0.01), MSNA (P Ͻ 0.01), heart rate (P Ͻ 0.01), and skin blood flow (P Ͻ 0.001), whereas mean arterial blood pressure did not change significantly (P Ͼ 0.05). During both normothermic and heat stress conditions, MSNA increased and then decreased significantly when blood pressure was lowered and then raised via intravenous bolus infusions of sodium nitroprusside and phenylephrine HCl, respectively. The slope of the relationship between MSNA and diastolic blood pressure during heat stress (Ϫ128.3 Ϯ 13.9 U ⅐ beats Ϫ1 ⅐ mmHg Ϫ1 ) was similar (P ϭ 0.31) with normothermia (Ϫ140.6 Ϯ 21.1 U ⅐ beats Ϫ1 ⅐ mmHg Ϫ1 ). Moreover, no significant change in the slope of the relationship between heart rate and systolic blood pressure was observed. These data suggest that arterial baroreflex modulation of MSNA and heart rate are not altered by whole body heating, with the exception of an upward shift of these baroreflex curves to accommodate changes in these variables that occur with whole body heating. baroreflex sensitivity; muscle sympathetic nerve activity; heart rate; heat stress DURING EXPOSURE TO INCREASED thermal load, humans become more susceptible to syncope during orthostatic or gravitational acceleration (1, 15). Baroreflexes are important in the regulation of blood pressure, but relatively little is known about the effects of whole body heating on baroreflex regulation. Previous studies revealed that electrical stimulation of the hypothalamus, which is the central neural structure governing thermoregulation (9, 20), modifies the baroreceptor reflex. Therefore, it is possible that whole body heating impairs baroreflex control of blood pressure, thereby contributing to the reduction in orthostatic tolerance during exposure to hyperthermic environmental conditions.Although the effects of whole body heating on baroreflex function have not been fully identified, during heat stress, baroreflexes remain capable of modulating efferent sympathetic nerve activity as evidenced by the observation that increases in blood pressure via phenylephrine HCl infusion decrease muscle sympathetic nerve activity (MSNA) in heat-stressed humans (3). Similar changes in splanchnic sympathetic nerve activity have been reported during blood pressure perturbations in hyperthermic rats (18).Previously, studies investigated the effects of heat stress on baroreflex function in rats (18, 22) and baboons (10). With the use of different techniques, these investigators concluded that hyperthermic exposu...

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Section: Discussionsupporting

confidence: 93%

Baroreflex modulation of sympathetic nerve activity to muscle in heat-stressed humans

Cui

Wilson

Crandall

2002

American Journal of Physiology-Regulatory, Integrative and Comp

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“…Muscle and skin sympathetic activity may increase with both heating and cooling (Normell & Wallin, 1974; Niimi et al . 1997; Cui et al . 2007).…”

Section: Discussionmentioning

confidence: 99%

Mechanisms for the control of local tissue blood flow during thermal interventions: influence of temperature‐dependent ATP release from human blood and endothelial cells

Kalsi

Chiesa

Trangmar

et al. 2017

Experimental Physiology

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New Findings What is the central question of this study? Skin and muscle blood flow increases with heating and decreases with cooling, but the temperature‐sensitive mechanisms underlying these responses are not fully elucidated. What is the main finding and its importance? We found that local tissue hyperaemia was related to elevations in ATP release from erythrocytes. Increasing intravascular ATP augmented skin and tissue perfusion to levels equal or above thermal hyperaemia. ATP release from isolated erythrocytes was altered by heating and cooling. Our findings suggest that erythrocytes are involved in thermal regulation of blood flow via modulation of ATP release. Local tissue perfusion changes with alterations in temperature during heating and cooling, but the thermosensitivity of the vascular ATP signalling mechanisms for control of blood flow during thermal interventions remains unknown. Here, we tested the hypotheses that the release of the vasodilator mediator ATP from human erythrocytes, but not from endothelial cells or other blood constituents, is sensitive to both increases and reductions in temperature and that increasing intravascular ATP availability with ATP infusion would potentiate thermal hyperaemia in limb tissues. We first measured blood temperature, brachial artery blood flow and plasma [ATP] during passive arm heating and cooling in healthy men and found that they increased by 3.0 ± 1.2°C, 105 ± 25 ml min−1 °C−1 and twofold, respectively, (all P < 0.05) with heating, but decreased or remained unchanged with cooling. In additional men, infusion of ATP into the brachial artery increased skin and deep tissue perfusion to levels equal or above thermal hyperaemia. In isolated erythrocyte samples exposed to different temperatures, ATP release increased 1.9‐fold from 33 to 39°C (P < 0.05) and declined by ∼50% at 20°C (P < 0.05), but no changes were observed in cultured human endothelial cells, plasma or serum samples. In conclusion, increases in plasma [ATP] and skin and deep tissue perfusion with limb heating are associated with elevations in ATP release from erythrocytes, but not from endothelial cells or other blood constituents. Erythrocyte ATP release is also sensitive to temperature reductions, suggesting that erythrocytes may function as thermal sensors and ATP signalling generators for control of tissue perfusion during thermal interventions.

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“…In addition, carotid baroreceptor stimulation of cutaneous vascular conductance is exaggerated in whole body heating in air (50). Muscle sympathetic nerve activity is increased during heat stress in air at rest, as is skin blood flow, heart rate, and cardiac output, while blood pressure is reduced (66,89). Sympathetic nerve activity may play a role in both thermal and blood pressure regulation during heat stress (66).…”

Section: Warm Watermentioning

confidence: 99%

“…Muscle sympathetic nerve activity is increased during heat stress in air at rest, as is skin blood flow, heart rate, and cardiac output, while blood pressure is reduced (66,89). Sympathetic nerve activity may play a role in both thermal and blood pressure regulation during heat stress (66). The increased sympathetic nerve activity during heat stress at rest is also evident during exercise (89).…”

Section: Warm Watermentioning

confidence: 99%

The underwater environment: cardiopulmonary, thermal, and energetic demands

Pendergast¹,

Lundgren²

2009

Journal of Applied Physiology

125

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Pendergast DR, Lundgren CE. The underwater environment: cardiopulmonary, thermal, and energetic demands. J Appl Physiol 106: 276 -283, 2009. First published November 26, 2008 doi:10.1152/japplphysiol.90984.2008.-Water covers over 75% of the earth, has a wide variety of depths and temperatures, and holds a great deal of the earth's resources. The challenges of the underwater environment are underappreciated and more short term compared with those of space travel. Immersion in water alters the cardio-endocrine-renal axis as there is an immediate translocation of blood to the heart and a slower autotransfusion of fluid from the cells to the vascular compartment. Both of these changes result in an increase in stroke volume and cardiac output. The stretch of the atrium and transient increase in blood pressure cause both endocrine and autonomic changes, which in the short term return plasma volume to control levels and decrease total peripheral resistance and thus regulate blood pressure. The reduced sympathetic nerve activity has effects on arteriolar resistance, resulting in hyperperfusion of some tissues, which for specific tissues is time dependent. The increased central blood volume results in increased pulmonary artery pressure and a decline in vital capacity. The effect of increased hydrostatic pressure due to the depth of submersion does not affect stroke volume; however, a bradycardia results in decreased cardiac output, which is further reduced during breath holding. Hydrostatic compression, however, leads to elastic loading of the chest wall and negative pressure breathing. The depthdependent increased work of breathing leads to augmented respiratory muscle blood flow. The blood flow is increased to all lung zones with some improvement in the ventilation-perfusion relationship. The cardiac-renal responses are time dependent; however, the increased stroke volume and cardiac output are, during head-out immersion, sustained for at least hours. Changes in water temperature do not affect resting cardiac output; however, maximal cardiac output is reduced, as is peripheral blood flow, which results in reduced maximal exercise performance. In the cold, maximal cardiac output is reduced and skin and muscle are vasoconstricted, resulting in a further reduction in exercise capacity. respiratory; renal; immersion; exercise; aging; sex differences; submersion; pressure; energy cost THE UNDERWATER ENVIRONMENT is unique, and while it is a magical place with great history and beauty and plant and animal life and holds a wealth of resources, it also imposes pronounced physiological stresses on humans and animals. This brief review offers an overview of how the major environmental challenges, i.e., the pressure, temperature extremes, and the unbreathable ambient medium, of the "Silent World" affect circulation, renal system and water balance, breathing, exercise, and thermal balance and how it imposes some threats due to pharmacological or toxic effects of respired gases at high pressure, i.e., great depths. Adaptations to ...

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Effect of heat stress on muscle sympathetic nerve activity in humans

Cited by 95 publications

References 13 publications

Baroreflex modulation of sympathetic nerve activity to muscle in heat-stressed humans

Baroreflex modulation of sympathetic nerve activity to muscle in heat-stressed humans

Mechanisms for the control of local tissue blood flow during thermal interventions: influence of temperature‐dependent ATP release from human blood and endothelial cells

The underwater environment: cardiopulmonary, thermal, and energetic demands

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