In:
American Journal of Physiology-Heart and Circulatory Physiology, American Physiological Society, Vol. 293, No. 1 ( 2007-07), p. H467-H473
Kurzfassung:
Dynamic cerebral autoregulation (CA) is challenged by exercise and may become less effective when exercise is exhaustive. Exercise may increase arterial glucose concentration, and we evaluated whether the cerebrovascular response to exercise is affected by hyperglycemia. The effects of a hyperinsulinemic euglycemic clamp (EU) and hyperglycemic clamp (HY) on the cerebrovascular (CVRI) and systemic vascular resistance index (SVRI) responses were evaluated in seven healthy subjects at rest and during rhythmic handgrip exercise. Transfer function analysis of the dynamic relationship between beat-to-beat changes in mean arterial pressure and middle cerebral artery (MCA) mean blood flow velocity ( V mean ) was used to assess dynamic CA. At rest, SVRI decreased with HY and EU ( P 〈 0.01). CVRI was maintained with EU but became reduced with HY [11% (SD 3); P 〈 0.01], and MCA V mean increased ( P 〈 0.05), whereas brain catecholamine uptake and arterial Pco 2 did not change significantly. HY did not affect the normalized low-frequency gain between mean arterial pressure and MCA V mean or the phase shift, indicating maintained dynamic CA. With HY, the increase in CVRI associated with exercise was enhanced (19 ± 7% vs. 9 ± 7%; P 〈 0.05), concomitant with a larger increase in heart rate and cardiac output and a larger reduction in SVRI (22 ± 4% vs. 14 ± 2%; P 〈 0.05). Thus hyperglycemia lowered cerebral vascular tone independently of CA capacity at rest, whereas dynamic CA remained able to modulate cerebral blood flow around the exercise-induced increase in MCA V mean . These findings suggest that elevated blood glucose does not explain that dynamic CA is affected during intense exercise.
Materialart:
Online-Ressource
ISSN:
0363-6135
,
1522-1539
DOI:
10.1152/ajpheart.00045.2007
Sprache:
Englisch
Verlag:
American Physiological Society
Publikationsdatum:
2007
ZDB Id:
1477308-9
SSG:
12
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