Middle cerebral artery blood velocity and cerebral blood flow and O2 uptake during dynamic exercise

Madsen, Peter; Sperling, Bjørn; Warming, T.; Schmidt, J. F.; Secher, Niels H.; Wildschiødtz, Gordon; Holm, Søren; Lassen, Niels A.

doi:10.1152/jappl.1993.74.1.245

Cited by 140 publications

(139 citation statements)

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“…7 In a later study from the same group, a more robust method (SPECT scanning) for determination of global CBF was applied, and it was then found that global CBF remained constant, whereas V mean still increased. 15 This inconsistency is not readily explained, and we believe that changes in the diameter of the MCA may take place in dynamic exercise, eg, the activation of the sympathetic nervous system may constrict the larger cerebral resistance vessels concomitant to an autoregulatory dilation of the smaller resistance vessels.…”

Section: Discussionmentioning

confidence: 97%

Transcranial Doppler is valid for determination of the lower limit of cerebral blood flow autoregulation.

Larsen

Olsen

Hansen

et al. 1994

Stroke

261

152

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Background and Purpose This study validates transcranial Doppler sonography (TCD) for determination of the lower limit of cerebral blood flow (CBF) autoregulation and establishes a relation between global CBF and mean flow velocity (V mean ) in the middle cerebral artery.Methods Relative changes in CBF and in V mean were compared in 12 normal volunteers (2 women and 10 men; median age, 30 years [range, 21 to 61 years]). Catheters was placed in the left radial artery and in the bulb of the right internal jugular vein, respectively. Baseline CBF was measured by single-photon emission computed tomography scanning; concomitantly, blood samples were drawn for calculation of the cerebral arteriovenous oxygen difference. Then changes in mean arterial pressure (MAP) were induced, and relative changes in global CBF were calculated according to Fick's principle assuming a constant cerebral oxygen metabolism. MAP was increased 30 mm Hg by norepinephrine infusion and was decreased by lower body negative pressure. V raean was

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Section: Discussionmentioning

confidence: 97%

Transcranial Doppler is valid for determination of the lower limit of cerebral blood flow autoregulation.

Larsen

Olsen

Hansen

et al. 1994

Stroke

261

152

View full text Add to dashboard Cite

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“…38). It has been a matter of debate whether physical activity is associated with an overall activation of the brain (30,39), but it is incontrovertible that exercise activates several regions of the brain in an intensity-dependent manner (16,44,57). Although the mechanical power output remained constant during exercise, increased difficulty in retaining power at the end of the hyperthermic cycle trial was reflected in the subjects' RPE, and it appears that brain areas associated with "central command" are activated when the "mental effort" associated with exercise is enhanced (58).…”

Section: Discussionmentioning

confidence: 99%

“…Global CBF was measured by the Kety-Schmidt technique in the desaturation mode with 133 Xe as the tracer (32,39,46). Cerebral plasma flow was calculated on the basis of the CBF and the corresponding hematocrit, and the cerebral uptake or release of a given substance was calculated as the cerebral plasma flow multiplied by the a-v difference of the substance.…”

Section: Methodsmentioning

confidence: 99%

Neurohumoral responses during prolonged exercise in humans

Nybo¹,

Nielsen²,

Blomstrand³

et al. 2003

Journal of Applied Physiology

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.-This study examined neurohumoral alterations during prolonged exercise with and without hyperthermia. The cerebral oxygen-to-carbohydrate uptake ratio (O 2/CHO ϭ arteriovenous oxygen difference divided by arteriovenous glucose difference plus one-half lactate), the cerebral balances of dopamine, and the metabolic precursor of serotonin, tryptophan, were evaluated in eight endurance-trained subjects during exercise randomized to be with or without hyperthermia. The core temperature stabilized at 37.9 Ϯ 0.1°C (mean Ϯ SE) in the control trial, whereas it increased to 39.7 Ϯ 0.2°C in the hyperthermic trial, with a concomitant increase in perceived exertion (P Ͻ 0.05). At rest, the brain had a small release of tryptophan (arteriovenous difference of Ϫ1.2 Ϯ 0.3 mol/l), whereas a net balance was obtained during the two exercise trials. Both the arterial and jugular venous dopamine levels became elevated during the hyperthermic trial, but the net release from the brain was unchanged. During exercise, the O2/CHO was similar across trials, but, during recovery from the hyperthermic trial, the ratio decreased to 3.8 Ϯ 0.3 (P Ͻ 0.05), whereas it returned to the baseline level of ϳ6 within 5 min after the control trial. The lowering of O2/CHO was established by an increased arteriovenous glucose difference (1.1 Ϯ 0.1 mmol/l during recovery from hyperthermia vs. 0.7 Ϯ 0.1 mmol/l in control; P Ͻ 0.05). The present findings indicate that the brain has an increased need for carbohydrates during recovery from strenuous exercise, whereas enhanced perception of effort as observed during exercise with hyperthermia was not related to alterations in the cerebral balances of dopamine or tryptophan.brain; dopamine; hyperthermia; tryptophan ALTHOUGH FATIGUE MAY RELATE to both peripheral (muscular) and central factors (4, 31, 52), attention has primarily been on the association to muscular factors. Hypotheses have connected central fatigue with alterations in the cerebral level of different neurotransmitters, but the cerebral balances of these neurotransmitters, their precursors, or metabolites have actually never been determined during prolonged exercise in humans. Central fatigue is aggravated by hyperthermia (47, 48), but the neurobiological mechanism(s) underlying this type of fatigue is unknown. Special attention has been given to the synthesis and metabolism of serotonin (5-hydroxytryptamine), because of its role in arousal, sleepiness, and mood (5, 13, 15, 42, 51). Cerebral serotonin kinetics cannot be assessed directly in humans, because its passage across the blood-brain barrier is limited (27). However, determination of the cerebral uptake of tryptophan (TRP), the precursor for the synthesis of serotonin, may provide an indication of changes in the serotonin level within the brain, because transport of TRP into the brain is the ratelimiting step in the synthesis of serotonin (5, 20). Some support for the involvement of serotonin in fatigue is obtained from studies that have attempted to alter the cerebral serotonin level by me...

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“…[22][23][24] This correlation, however, could not be substantiated by other investigations. 25 There is no data regarding these features in patients with liver diseases.…”

Section: Discussionmentioning

confidence: 99%

Increased cerebrovascular resistance in cirrhotic patients with ascites

et al. 1998

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Studies assessing regional hemodynamics in patients with cirrhosis and ascites have shown vasodilation in the splanchnic circulation and vasoconstriction in the renal circulation and in the brachial and femoral artery vascular territories. The aim of this study was to assess the cerebral vascular resistance in cirrhotic patients with ascites. The resistive index in the middle cerebral artery (an index of the cerebral vascular resistance) and in a renal interlobar artery were measured by Doppler ultrasonography in 7 healthy subjects: 13 patients with compensated cirrhosis and 24 patients with ascites (13 with renal failure). The arterial blood pressure and the activity of the renin-angiotensin and sympathetic nervous systems, as estimated by plasma renin activity and plasma norepinephrine concentration, respectively, were also measured. The resistive index in the middle cerebral artery was significantly increased in patients with ascites (0.68 ؎ 0.05, mean ؎ SD) as compared with patients without ascites (0.60 ؎ 0.01, P F .05) and with healthy patients (0.52 ؎ 0.01, P F .01). Renal resistive index was also increased in patients with ascites (0.77 ؎ 0.01) compared with the other two groups (0.68 ؎ 0.02 and 0.62 ؎ 0.00, respectively; P F .001). The resistive index in the middle cerebral artery showed a direct correlation with renal resistive index (r ‫؍‬ .73, P F .01), plasma renin activity (r ‫؍‬ .61, P F .01), and norepinephrine (r ‫؍‬ .53, P F .01). The resistive index in the middle cerebral artery showed an inverse correlation with mean arterial pressure (r ‫,54.؊؍‬ P F .01). These results indicate that in patients with cirrhosis and ascites there is a cerebral vasoconstriction which is probably related with the arterial hypotension and the overactivity of vasoconstrictor systems. (HEPATOL-OGY 1998;28:39-44.)Portal hypertension in cirrhosis is associated with a hyperdynamic circulation, which is characterized by hypervolemia, high cardiac output, arterial hypotension, and low peripheral vascular resistance. 1 These circulatory abnormalities are thought to be secondary to a splanchnic arteriolar vasodilation related to the increase in portal pressure. Portal hypertension in experimental animals is associated with a generalized splanchnic arteriolar vasodilation. 2,3 There is indirect evidence that this also occurs in human cirrhosis, as hepatic blood flow is usually normal or increased in these patients, even though 60% to 80% of portal flow is shunted through the collateral circulation. 4 In addition, the mean transit time in the splanchnic vascular bed is substantially reduced in alcoholic cirrhotic patients, which indicates a hyperkinetic splanchnic circulation in these patients. 5 Finally, studies using echo-Doppler have documented increased splenic and mesenteric blood flow in patients with cirrhosis. 6,7 Investigations assessing regional circulations in human cirrhosis are also consistent with that concept. Renal blood flow is reduced and renal vascular resistance is increased in most patients with cirrhosi...

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Middle cerebral artery blood velocity and cerebral blood flow and O2 uptake during dynamic exercise

Cited by 140 publications

References 0 publications

Transcranial Doppler is valid for determination of the lower limit of cerebral blood flow autoregulation.

Transcranial Doppler is valid for determination of the lower limit of cerebral blood flow autoregulation.

Neurohumoral responses during prolonged exercise in humans

Increased cerebrovascular resistance in cirrhotic patients with ascites

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