Your ageing brain: the lows and highs of cerebral metabolism

Ainslie, Philip N.; Bailey, Damian Miles

doi:10.1113/jphysiol.2012.250548

Cited by 8 publications

(6 citation statements)

References 4 publications

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“…1B), indicating that although a major part of the reduction in MCAv mean with age is related to the lower PaCO 2 , other factors are also involved. It has been suggested that differences in PaCO 2 may account for 30% of the age-related decline in MCAv mean (1), and thus according to the present study this may be somewhat an underestimate. As MCAv mean and PaCO 2 in young and old participants present an age-related difference already at rest, the difference observed during exercise could derive from here.…”

Section: Discussionmentioning

confidence: 44%

“…One reason for the discrepancies could be related to the use of humans over a narrow age range, and with varying degrees of physical fitness. Thus a further aim related to this study was to quantify CO 2 reactivity and to investigate its association to the decrease in MCAv mean with age.A high aerobic fitness level appears to attenuate the agerelated decline in resting CBF (39) and MCAv mean (1)(2)(3)46), although this has not been universally observed (4, 49). …”

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confidence: 99%

“…A high aerobic fitness level appears to attenuate the agerelated decline in resting CBF (39) and MCAv mean (1)(2)(3)46), although this has not been universally observed (4, 49).…”

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confidence: 99%

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Age, aerobic fitness, and cerebral perfusion during exercise: role of carbon dioxide

Flück

Bráz

Keiser

et al. 2014

American Journal of Physiology-Heart and Circulatory Physiology

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Middle cerebral artery mean velocity (MCAvmean) is attenuated with increasing age both at rest and during exercise. The aim of this study was to determine the influence of the age-dependent reduction in arterial PCO2 (PaCO2) and physical fitness herein. We administered supplemental CO2 (CO2 trial) or no additional gas (control trial) to the inspired air in a blinded and randomized manner, and assessed middle cerebral artery mean flow velocity during graded exercise in 1) 21 young [Y; age 24 Ϯ 3 yr (ϮSD)] volunteers of whom 11 were trained (YT) and 10 considered untrained (YUT), and 2) 17 old (O; 66 Ϯ 4 yr) volunteers of whom 8 and 9 were considered trained (OT) and untrained (OUT), respectively. A resting hypercapnic reactivity test was also performed. MCAvmean and PaCO2 were lower in O [44.9 Ϯ 3.1 cm/s and 30 Ϯ 1 mmHg (ϮSE)] compared with Y (59.3 Ϯ 2.3 cm/s and 34 Ϯ 1 mmHg, P Ͻ 0.01) at rest, independent of aerobic fitness level. The age-related decreases in MCAvmean and PaCO2 persisted during exercise. Supplemental CO2 reduced the age-associated decline in MCAv mean by 50%, suggesting that PaCO2 is a major component in the decline. On the other hand, relative hypercapnic reactivity was neither influenced by age (P ϭ 0.46) nor aerobic fitness (P ϭ 0.36). Although supplemental CO2 attenuated exercise-induced reduction in cerebral oxygenation (near-infrared spectroscopy), this did not influence exercise performance. In conclusion, PaCO2 contributes to the age-associated decline in MCAvmean at rest and during exercise; however exercise capacity did not diminish this age effect. brain blood flow; middle cerebral artery; old; transcranial Doppler CEREBRAL BLOOD FLOW (CBF) is meticulously regulated to ensure an adequate perfusion of the brain. With exercise middle cerebral artery mean velocity (MCAv mean ; a surrogate measure of CBF) is increased until ϳ60% of maximal oxygen uptake (V O 2max ) but thereafter declines toward resting levels (10,20,28). In young healthy individuals this drop in cerebral perfusion is likely the consequence of a hyperventilation facilitated reduction in PaCO 2 and hence augmented cerebral vasoconstriction (39). Accordingly, administration of CO 2 to the inspired air during exercise abolishes the decrease in MCAv mean (44,45), and during vigorous exercise MCAv mean is regulated by PaCO 2 and only to a lesser extent influenced by cerebral metabolism, mean arterial pressure (MAP), cardiac output, or sympathetic nerve activity (35).Compared with young healthy individuals a reduced CBF (24) and MCAv mean has consistently been reported in the aged population both at rest (2,7,9,15,25,27,49) and during exercise (9,10,28,32). Although a reduced MCAv mean response in aged humans is observed with exercise, its pattern follows that of young individuals, i.e., an initial increase which is then followed by a decline as the exercise intensity becomes intense (9,10,28,32). The regulating mechanisms for the reduction in CBF with age remain uncertain and global brain atrophy (11), decreased neuronal activ...

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Section: Discussionmentioning

confidence: 44%

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confidence: 99%

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Age, aerobic fitness, and cerebral perfusion during exercise: role of carbon dioxide

Flück

Bráz

Keiser

et al. 2014

American Journal of Physiology-Heart and Circulatory Physiology

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“…Even though in older vs. younger individuals CBF is lower during exercise, brain uptake of O 2 is similar (23). In the later stages of exercise the reduction of the increased CBF to baseline is attributed to the effects of hypocapnia on cerebrovascular conductance (1,71). Brain function deteriorates when its oxygenation is reduced by more than 10% from the resting level (27,61,112) in contrast to skeletal muscles tolerating ϳ90% O 2 desaturation (3).…”

Section: Cbf Oxygen Delivery and Ageingmentioning

confidence: 99%

Hyperventilation, cerebral perfusion, and syncope

Immink

Pott

Secher

et al. 2014

Journal of Applied Physiology

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This review summarizes evidence in humans for an association between hyperventilation (HV)-induced hypocapnia and a reduction in cerebral perfusion leading to syncope defined as transient loss of consciousness (TLOC). The cerebral vasculature is sensitive to changes in both the arterial carbon dioxide (PaCO2) and oxygen (PaO2) partial pressures so that hypercapnia/hypoxia increases and hypocapnia/hyperoxia reduces global cerebral blood flow. Cerebral hypoperfusion and TLOC have been associated with hypocapnia related to HV. Notwithstanding pronounced cerebrovascular effects of PaCO2 the contribution of a low PaCO2 to the early postural reduction in middle cerebral artery blood velocity is transient. HV together with postural stress does not reduce cerebral perfusion to such an extent that TLOC develops. However when HV is combined with cardiovascular stressors like cold immersion or reduced cardiac output brain perfusion becomes jeopardized. Whether, in patients with cardiovascular disease and/or defect, cerebral blood flow cerebral control HV-induced hypocapnia elicits cerebral hypoperfusion, leading to TLOC, remains to be established.

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“…CBF control is multifactorial, influenced largely by the partial pressure of arterial carbon dioxide, mean arterial pressure and cerebral metabolism. 1 Despite the abundance of sympathetic nerve fibres emanating from the cervical and stellate ganglia that innervate the cerebral arteries, the role of the autonomic nervous system in the control of cerebral blood flow (CBF) in humans has remained contentious for decades. 2–10…”

Section: Introductionmentioning

confidence: 99%

Middle cerebral artery diameter changes during rhythmic handgrip exercise in humans

Verbree

Bronzwaer

Buchem

et al. 2016

J Cereb Blood Flow Metab

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Transcranial Doppler (TCD) sonography is a frequently employed technique for quantifying cerebral blood flow by assuming a constant arterial diameter. Given that exercise increases arterial pressure by sympathetic activation, we hypothesized that exercise might induce a change in the diameter of large cerebral arteries. Middle cerebral artery (MCA) cross-sectional area was assessed in response to handgrip exercise by direct magnetic resonance imaging (MRI) observations. Twenty healthy subjects (11 female) performed three 5 min bouts of rhythmic handgrip exercise at 60% maximum voluntary contraction, alternated with 5 min of rest. High-resolution 7 T MRI scans were acquired perpendicular to the MCA. Two blinded observers manually determined the MCA cross-sectional area. Sufficient image quality was obtained in 101 MCA-scans of 19 subjects (age-range 20-59 years). Mixed effects modelling showed that the MCA cross-sectional area decreased by 2.1 ± 0.8% (p = 0.01) during handgrip, while the heart rate increased by 11 ± 2% (p < 0.001) at constant end-tidal CO (p = 0.10). In conclusion, the present study showed a 2% decrease in MCA cross-sectional area during rhythmic handgrip exercise. This further strengthens the current concept of sympathetic control of large cerebral arteries, showing in vivo vasoconstriction during exercise-induced sympathetic activation. Moreover, care must be taken when interpreting TCD exercise studies as diameter constancy cannot be assumed.

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Your ageing brain: the lows and highs of cerebral metabolism

Cited by 8 publications

References 4 publications

Age, aerobic fitness, and cerebral perfusion during exercise: role of carbon dioxide

Age, aerobic fitness, and cerebral perfusion during exercise: role of carbon dioxide

Hyperventilation, cerebral perfusion, and syncope

Middle cerebral artery diameter changes during rhythmic handgrip exercise in humans

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