Point: Humans do demonstrate selective brain cooling during hyperthermia

White, Matthew D.; Greiner, Jesse; McDonald, Patrick L. L.

doi:10.1152/japplphysiol.00992.2010

Cited by 27 publications

(23 citation statements)

References 23 publications

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“…The physiological significance of hyperthermia-induced hyperventilation in humans remains controversial (11,53). Although it has been proposed that this hyperventilation is a thermoregulatory response for selectively cooling the brain (50), it reportedly leads to hypocapnia and reductions in cerebral blood flow (16,22,41,42), which would reduce heat exchange in the brain and thus increase brain temperature (43).…”

Section: Discussionmentioning

confidence: 99%

Comparison of hyperthermic hyperventilation during passive heating and prolonged light and moderate exercise in the heat

Tsuji

Honda

Fujii

et al. 2012

Journal of Applied Physiology

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Elevation of core temperature leads to increases in ventilation in both resting subjects and those engaged in prolonged exercise. We compared the characteristics of the hyperthermic hyperventilation elicited during passive heating at rest and during prolonged moderate and light exercise. Twelve healthy men performed three trials: a rest trial in which subjects were passively heated using hot-water immersion (41°C) and a water-perfused suit and two exercise trials in which subjects exercised at 25% (light) or 50% (moderate) of peak oxygen uptake in the heat (37°C and 50% relative humidity) after first using water immersion (18°C) to reduce resting esophageal temperature (T(es)). This protocol enabled detection of a T(es) threshold for hyperventilation during the exercise. When minute ventilation (Ve) was expressed as a function of T(es), 9 of the 12 subjects showed T(es) thresholds for hyperventilation in all trials. The T(es) thresholds for increases in Ve during light and moderate exercise (37.1 ± 0.4 and 36.9 ± 0.4°C) were both significantly lower than during rest (38.3 ± 0.6°C), but the T(es) thresholds did not differ between the two exercise intensities. The sensitivity of Ve to increasing T(es) (slope of the T(es)-Ve relation) above the threshold was significantly lower during moderate exercise (8.7 ± 3.5 l · min(-1) · °C(-1)) than during rest (32.5 ± 24.2 l · min(-1) · °C(-1)), but the sensitivity did not differ between light (10.4 ± 13.0 l · min(-1) · °C(-1)) and moderate exercise. These results suggest the core temperature threshold for hyperthermic hyperventilation and the hyperventilatory response to increasing core temperature in passively heated subjects differs from that in exercising subjects, irrespective of whether the exercise is moderate or light.

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Section: Discussionmentioning

confidence: 99%

Comparison of hyperthermic hyperventilation during passive heating and prolonged light and moderate exercise in the heat

Tsuji

Honda

Fujii

et al. 2012

Journal of Applied Physiology

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“…Even in those animals without a carotid rete, arterial blood in the carotid arteries passes close to the cavernous sinus and may be cooled by venous blood draining from the nasal surfaces (231). The existence of selective brain cooling by this mechanism in humans, which lack a carotid rete system, remains controversial (289).…”

Section: Pantingmentioning

confidence: 99%

Coordination of Breathing with Nonrespiratory Activities

Bartlett¹,

Leiter²

2012

Comprehensive Physiology

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Many articles in this section of Comprehensive Physiology are concerned with the development and function of a central pattern generator (CPG) for the control of breathing in vertebrate animals. The action of the respiratory CPG is extensively modified by cortical and other descending influences as well as by feedback from peripheral sensory systems. The central nervous system also incorporates other CPGs, which orchestrate a wide variety of discrete and repetitive, voluntary and involuntary movements. The coordination of breathing with these other activities requires interaction and coordination between the respiratory CPG and those governing the nonrespiratory activities. Most of these interactions are complex and poorly understood. They seem to involve both conventional synaptic crosstalk between groups of neurons and fluid identity of neurons as belonging to one CPG or another: neurons that normally participate in breathing may be temporarily borrowed or hijacked by a competing or interrupting activity. This review explores the control of breathing as it is influenced by many activities that are generally considered to be nonrespiratory. The mechanistic detail varies greatly among topics, reflecting the wide variety of pertinent experiments.

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“…The physiological significance of hyperthermic hyperventilation in humans remains controversial (8,44). For example, White and colleague (41,44) proposed that human hyperthermic hyperventilation has a role for thermoregulation, i.e., it contributes to selective brain cooling.…”

Section: Perspectives and Significancementioning

confidence: 99%

“…For example, White and colleague (41,44) proposed that human hyperthermic hyperventilation has a role for thermoregulation, i.e., it contributes to selective brain cooling. At variance with this notion is the findings that hyperthermic hyperventilation in humans usually leads to hypocapnia and reduced cerebral blood flow (10,15,36), which in turn induces a reduction in heat exchange in the brain and thus increases in brain temperature (34).…”

Section: Perspectives and Significancementioning

confidence: 99%

Effect of initial core temperature on hyperthermic hyperventilation during prolonged submaximal exercise in the heat

Tsuji

Honda

Fujii

et al. 2012

American Journal of Physiology-Regulatory, Integrative and Comp

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Nishiyasu T. Effect of initial core temperature on hyperthermic hyperventilation during prolonged submaximal exercise in the heat. Am J Physiol Regul Integr Comp Physiol 302: R94 -R102, 2012. First published September 28, 2011 doi:10.1152/ajpregu.00048.2011.-We investigated whether a core temperature threshold for hyperthermic hyperventilation is seen during prolonged submaximal exercise in the heat when core temperature before the exercise is reduced and whether the evoked hyperventilatory response is affected by altering the initial core temperature. Ten male subjects performed three exercise trials at 50% of peak oxygen uptake in the heat (37°C and 50% relative humidity) after altering their initial esophageal temperature (Tes). Initial Tes was manipulated by immersion for 25 min in water at 18°C (Precooling), 35°C (Control), or 40°C (Preheating). Tes after the water immersion was significantly higher in the Preheating trial (37.5 Ϯ 0.3°C) and lower in the Precooling trial (36.1 Ϯ 0.3°C) than in the Control trial (36.9 Ϯ 0.3°C). In the Precooling trial, minute ventilation (V E) showed little change until Tes reached 37.1 Ϯ 0.4°C. Above this core temperature threshold, V E increased linearly in proportion to increasing Tes. In the Control trial, V E increased as Tes increased from 37.0°C to 38.6°C after the onset of exercise. In the Preheating trial, V E increased from the initially elevated levels of Tes (from 37.6 to 38.6°C) and V E. The sensitivity of V E to increasing Tes above the threshold for hyperventilation (the slope of the Tes-V E relation) did not significantly vary across trials (Precooling trial ϭ 10.6 Ϯ 5.9, Control trial ϭ 8.7 Ϯ 5.1, and Preheating trial ϭ 9.2 Ϯ 6.9 L·min Ϫ1 ·°C Ϫ1 ). These results suggest that during prolonged submaximal exercise at a constant workload in humans, there is a clear core temperature threshold for hyperthermic hyperventilation and that the evoked hyperventilatory response is unaffected by altering initial core temperature.hyperpnea; hyperthermia; thermoregulation; precooling; preheating WHEN HUMANS ARE EXPOSED TO a hot environment, heat dissipation through cutaneous vasodilation and sweating increases in response to rising body core and skin temperatures. In addition to these thermoregulatory responses, Haldane found in 1905 that an increase in ventilation is also induced by a rise in body core temperature (13). Since that early report, many studies have confirmed the existence of hyperthermia-induced hyperventilation (5, 9 -11, 16, 26, 32, 38, 43) although its characteristic and significance remain unclear.When ventilation is expressed as a function of core temperature in passively-heated humans at rest, there is no significant change until core temperature reaches a temperature threshold for hyperventilation, ϳ37.8 -38.5°C. Above this threshold, ventilation increases linearly in proportion to increasing core temperature with minimal change in oxygen consumption (5, 10). As in resting subjects, metabolic factors contribute minimally to ventilation during prolo...

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Point: Humans do demonstrate selective brain cooling during hyperthermia

Cited by 27 publications

References 23 publications

Comparison of hyperthermic hyperventilation during passive heating and prolonged light and moderate exercise in the heat

Comparison of hyperthermic hyperventilation during passive heating and prolonged light and moderate exercise in the heat

Coordination of Breathing with Nonrespiratory Activities

Effect of initial core temperature on hyperthermic hyperventilation during prolonged submaximal exercise in the heat

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