From the Divisions of Medical Physics and Surgery, Faculty of Medicine,
University of Leicester, Leicester, United Kingdom.
Correspondence to Dr J. Dumville, Department of Medical Physics, Leicester Royal Infirmary, Leicester LE1 5WW, UK. E-mail jd23{at}le.ac.uk
Background and Purpose—Conventional
methods of assessing cerebrovascular reactivity (CVR) omit the
influence of blood pressure (BP). This study demonstrates the
significant influence of BP during the assessment of CVR in patients
with carotid artery disease.
Methods—In 56 subjects the CVR was bilaterally assessed by
measurement of cerebral blood flow velocity change in response to
inhalation of 5% CO2 in air while BP was continuously
monitored. Three methods of calculating the CVR were used: the
conventional ratio between relative cerebral blood flow velocity and
end-tidal CO2, simple linear regression, and multiple
linear regression analysis (MLRA). The clinical significance of
the difference in CVR indices was evaluated. The Bland-Altman test was
applied to quantify the comparability and bias between measurements.
The magnitude and significance of a change in BP during the CVR
assessment were calculated in conjunction with an estimate of the
velocity change attributed to the BP. The statistical significance of
the data segment length on the variability and magnitude of the CVR
index was computed.
Results—The value of the CVR index was reduced by 20% and 6% in
comparison to the conventional ratio approach when MLRA and linear
regression were applied, respectively. With the use of MLRA, in 96% of
cases the value of the BP coefficient was statistically significant,
and in four patients the increase in velocity was primarily attributed
to the increase in BP.
Conclusions—The influence of BP is significant and requires
consideration when the CVR index is calculated in patients with carotid
artery disease.
© 1998 American Heart Association, Inc.
Original Contributions
Can Cerebrovascular Reactivity Be Assessed Without Measuring Blood Pressure in Patients With Carotid Artery Disease?
Key Words: blood pressure • carotid artery diseases • cerebrovascular reactivity
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