Standing up to the challenge of standing: a siphon does not support cerebral blood flow in humans

Dawson, Ellen A.; Secher, Niels H.; Dalsgaard, Mads K.; Ogoh, Shigehiko; Yoshiga, Chie C.; González‐Alonso, José; Steensberg, Adam; Raven, Peter B.

doi:10.1152/ajpregu.00196.2004

Cited by 76 publications

(80 citation statements)

References 18 publications

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“…Equally, MR remains stable during the initial 45 to 50 mins of prolonged cycling, but, when the subject struggles to continue, MR decreases and more so with heat stress (Nybo et al, 2003b). Conversely, if the workload requires full attention from the very onset of exercise, MR already reaches its nadir after 90 secs (Gonzalez-Alonso et al, 2004). Together, these observations support that MR decreases when exercise cannot be performed 'automatically' and requires a determined effort (Dalsgaard et al, 2002).…”

Section: The Mental Effort To Exercisementioning

confidence: 81%

“…The MR is not significantly reduced during exercise, but it becomes so in the immediate recovery period (P < 0.05) (Dalsgaard et al, 2002(Dalsgaard et al, , 2003(Dalsgaard et al, , 2004aGonzalez-Alonso et al, 2004;Nybo et al, 2003b).…”

Section: Paradigm Of Cerebral Activationmentioning

confidence: 91%

“…For example, moderate exercise at an arterial lactate concentration greater than 3 mmol/L is associated with slight lactate uptake by the brain (Ahlborg and Wahren, 1972;Dalsgaard et al, 2002). Indeed, when maximal exercise raises the arterial lactate concentrations to B15 mmol/L or higher, the cerebral lactate uptake (in molar amounts) may exceed that of glucose ( Figure 3) (Dalsgaard et al, 2002(Dalsgaard et al, , 2004bGonzalez-Alonso et al, 2004;Ide et al, 2000b). With such marked concentration gradient from blood to brain, lactate would be expected to reach high concentrations locally in the extracellular fluid of importance for the cellular uptake.…”

Section: Lactatementioning

confidence: 99%

“…For maximal exercise: different from the start, *P < 0.05; and peak value, w P < 0.05. Modified from Gonzalez-Alonso et al (2004).…”

Section: The Cerebral Metabolic Ratiomentioning

confidence: 99%

“…Also, with exercise in an awkward position as semisupine cycling, performance probably becomes limited at lower workloads and MR is reduced to 3.7 (Dalsgaard et al, 2002;Ide et al, 2000b), while for open-loop exercise at a low workload, continuation becomes a matter of endurance and MR decreases more (Dalsgaard et al, 2004a). Furthermore, when athletic cyclists reach their limit under familiar conditions in the heat, MR drops to 3 (Gonzalez- Alonso et al, 2004).…”

Section: Paradigm Of Cerebral Activationmentioning

confidence: 99%

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Fuelling Cerebral Activity in Exercising Man

Dalsgaard

2005

J Cereb Blood Flow Metab

137

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The metabolic response to brain activation in exercise might be expressed as the cerebral metabolic ratio (MR; uptake O 2 /glucose + 1/2 lactate). At rest, brain energy is provided by a balanced oxidation of glucose as MR is close to 6, but activation provokes a 'surplus' uptake of glucose relative to that of O 2 . Whereas MR remains stable during light exercise, it is reduced by 30% to 40% when exercise becomes demanding. The MR integrates metabolism in brain areas stimulated by sensory input from skeletal muscle, the mental effort to exercise and control of exercising limbs. The MR decreases during prolonged exhaustive exercise where blood lactate remains low, but when vigorous exercise raises blood lactate, the brain takes up lactate in an amount similar to that of glucose. This lactate taken up by the brain is oxidised as it does not accumulate within the brain and such pronounced brain uptake of substrate occurs independently of plasma hormones. The 'surplus' of glucose equivalents taken up by the activated brain may reach B10 mmol, that is, an amount compatible with the global glycogen level. It is suggested that a low MR predicts shortage of energy that ultimately limits motor activation and reflects a biologic background for 'central fatigue'.

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Section: The Mental Effort To Exercisementioning

confidence: 81%

Section: Paradigm Of Cerebral Activationmentioning

confidence: 91%

Section: Lactatementioning

confidence: 99%

“…For maximal exercise: different from the start, *P < 0.05; and peak value, w P < 0.05. Modified from Gonzalez-Alonso et al (2004).…”

Section: The Cerebral Metabolic Ratiomentioning

confidence: 99%

Section: Paradigm Of Cerebral Activationmentioning

confidence: 99%

See 3 more Smart Citations

Fuelling Cerebral Activity in Exercising Man

Dalsgaard

2005

J Cereb Blood Flow Metab

137

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The Brain and Fatigue

Noakes

Crewe

Tucker

2008

Olympic Textbook of Science in Sport

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Mass Transport: Circulatory System with Emphasis on Nonendothermic Species

Crossley

Burggren

Reiber

et al. 2016

Comprehensive Physiology

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Mass transport can be generally defined as movement of material matter. The circulatory system then is a biological example given its role in the movement in transporting gases, nutrients, wastes, and chemical signals. Comparative physiology has a long history of providing new insights and advancing our understanding of circulatory mass transport across a wide array of circulatory systems. Here we focus on circulatory function of nonmodel species. Invertebrates possess diverse convection systems; that at the most complex generate pressures and perform at a level comparable to vertebrates. Many invertebrates actively modulate cardiovascular function using neuronal, neurohormonal, and skeletal muscle activity. In vertebrates, our understanding of cardiac morphology, cardiomyocyte function, and contractile protein regulation by Ca2+ highlights a high degree of conservation, but differences between species exist and are coupled to variable environments and body temperatures. Key regulators of vertebrate cardiac function and systemic blood pressure include the autonomic nervous system, hormones, and ventricular filling. Further chemical factors regulating cardiovascular function include adenosine, natriuretic peptides, arginine vasotocin, endothelin 1, bradykinin, histamine, nitric oxide, and hydrogen sulfide, to name but a few. Diverse vascular morphologies and the regulation of blood flow in the coronary and cerebral circulations are also apparent in nonmammalian species. Dynamic adjustments of cardiovascular function are associated with exercise on land, flying at high altitude, prolonged dives by marine mammals, and unique morphology, such as the giraffe. Future studies should address limits of gas exchange and convective transport, the evolution of high arterial pressure across diverse taxa, and the importance of the cardiovascular system adaptations to extreme environments. © 2017 American Physiological Society. Compr Physiol 7:17-66, 2017.

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Standing up to the challenge of standing: a siphon does not support cerebral blood flow in humans

Cited by 76 publications

References 18 publications

Fuelling Cerebral Activity in Exercising Man

Fuelling Cerebral Activity in Exercising Man

The Brain and Fatigue

Mass Transport: Circulatory System with Emphasis on Nonendothermic Species

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