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Evaluation of the cerebral hemodynamic response to rhythmic handgrip
Departments of Neurological Surgery and Radiology, University of Texas Southwestern Medical Center, Dallas, Texas 75235-8855 The response of the cerebral circulation to exercise has been studied with transcranial Doppler ultrasound (TCD) because this modality provides continuous measurements of bloo...
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Published in: | Journal of applied physiology (1985) 2000-06, Vol.88 (6), p.2205-2213 |
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Main Authors: | , , , |
Format: | Article |
Language: | English |
Subjects: | |
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Summary: | Departments of Neurological Surgery and Radiology,
University of Texas Southwestern Medical Center, Dallas, Texas
75235-8855
The
response of the cerebral circulation to exercise has been studied with
transcranial Doppler ultrasound (TCD) because this modality provides
continuous measurements of blood velocity and is well suited for the
exercise environment. The use of TCD as an index of cerebral blood
flow, however, requires the assumption that the diameter of the
insonated vessel is constant. Here, we examine this assumption for
rhythmic handgrip using a spectral index designed to measure trends in
vessel flow. Nineteen normal subjects were studied during 5 min of
volitional maximum rhythmic right handgrip at 1 Hz. TCD velocities from
both middle arteries (left and right), blood pressure, and end-tidal
P CO 2 were recorded every 10 s. A spectral
weighted sum was also calculated as a flow index (FI). Averages were
computed from the last 2 min of handgrip. Relative changes in velocity,
FI, and pressure were calculated. The validity of FI was tested by
comparing the change in diameter derived from equations relating flow
and diameter. Mean blood pressure increased 23.8 ± 17.8% (SD), and
velocity increased 13.3 ± 9.8% (left) and 9.6 ± 8.3% (right).
Although the mean change in FI was small [2.0 ± 18.2% (left)
and 4.7 ± 29.7% (right)], the variation was high: some
subjects showed a significant increase in FI and others a significant
decrease. Diameter estimates from two equations relating flow and
luminal area were not significantly different. Decreases in FI were
associated with estimated diameter decreases of 10%. Our data suggest
that the cerebral blood flow (CBF) response to rhythmic handgrip is
heterogeneous and that middle cerebral artery flow can decrease in some
subjects, in agreement with prior studies using the Kety-Schmidt
technique. We speculate that the velocity increase is due to
sympathetically mediated vasoconstriction rather than a ubiquitous flow
increase. Our data suggest that the use of ordinary TCD velocities to
interpret the CBF response during exercise may be invalid.
transcranial Doppler; exercise; cerebral blood flow |
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ISSN: | 8750-7587 1522-1601 |
DOI: | 10.1152/jappl.2000.88.6.2205 |