Assessment of middle cerebral artery diameter during hypocapnia and hypercapnia in humans using ultra-high-field MRI
In the evaluation of cerebrovascular CO 2 reactivity measurements, it is often assumed that the diameter of the large intracranial arteries insonated by transcranial Doppler remains unaffected by changes in arterial CO 2 partial pressure. However, the strong cerebral vasodilatory capacity of CO 2 ch...
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Published in | Journal of applied physiology (1985) Vol. 117; no. 10; pp. 1084 - 1089 |
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Main Authors | , , , , , , , , |
Format | Journal Article |
Language | English |
Published |
United States
American Physiological Society
15.11.2014
|
Subjects | |
Online Access | Get full text |
ISSN | 8750-7587 1522-1601 1522-1601 |
DOI | 10.1152/japplphysiol.00651.2014 |
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Summary: | In the evaluation of cerebrovascular CO
2
reactivity measurements, it is often assumed that the diameter of the large intracranial arteries insonated by transcranial Doppler remains unaffected by changes in arterial CO
2
partial pressure. However, the strong cerebral vasodilatory capacity of CO
2
challenges this assumption, suggesting that there should be some changes in diameter, even if very small. Data from previous studies on effects of CO
2
on cerebral artery diameter [middle cerebral artery (MCA)] have been inconsistent. In this study, we examined 10 healthy subjects (5 women, 5 men, age 21–30 yr). High-resolution (0.2 mm in-plane) MRI scans at 7 Tesla were used for direct observation of the MCA diameter during hypocapnia, −1 kPa (−7.5 mmHg), normocapnia, 0 kPa (0 mmHg), and two levels of hypercapnia, +1 and +2 kPa (7.5 and 15 mmHg), with respect to baseline. The vessel lumen was manually delineated by two independent observers. The results showed that the MCA diameter increased by 6.8 ± 2.9% in response to 2 kPa end-tidal Pco
2
(Pet
CO
2
) above baseline. However, no significant changes in diameter were observed at the −1 kPa (−1.2 ± 2.4%), and +1 kPa (+1.4 ± 3.2%) levels relative to normocapnia. The nonlinear response of the MCA diameter to CO
2
was fitted as a continuous calibration curve. Cerebral blood flow changes measured by transcranial Doppler could be corrected by this calibration curve using concomitant Pet
CO
2
measurements. In conclusion, the MCA diameter remains constant during small deviations of the Pet
CO
2
from normocapnia, but increases at higher Pet
CO
2
values. |
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Bibliography: | SourceType-Scholarly Journals-1 ObjectType-Feature-1 content type line 14 ObjectType-Article-2 content type line 23 ObjectType-Article-1 ObjectType-Feature-2 |
ISSN: | 8750-7587 1522-1601 1522-1601 |
DOI: | 10.1152/japplphysiol.00651.2014 |