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J Appl Physiol (1985). 2014 Nov 15;117(10):1084-9. doi: 10.1152/japplphysiol.00651.2014. Epub 2014 Sep 4.

Assessment of middle cerebral artery diameter during hypocapnia and hypercapnia in humans using ultra-high-field MRI.

Author information

1
Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands; C. J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands; j.verbree@lumc.nl.
2
Laboratory for Clinical Cardiovascular Physiology, Academic Medical Center, Amsterdam, The Netherlands; Department of Internal Medicine, Academic Medical Center, Amsterdam, The Netherlands; and.
3
Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands; C. J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands;
4
Department of Pathology, Academic Medical Center, Amsterdam, The Netherlands;
5
Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands;
6
Department of Anesthesiology, Leiden University Medical Center, Leiden, The Netherlands;
7
Laboratory for Clinical Cardiovascular Physiology, Academic Medical Center, Amsterdam, The Netherlands; Department of Internal Medicine, Academic Medical Center, Amsterdam, The Netherlands; and MRC/Arthritis Research UK Centre for Musculoskeletal Ageing Research, School of Life Sciences, University of Nottingham Medical School, Queen's Medical Centre, Nottingham, United Kingdom.

Abstract

In the evaluation of cerebrovascular CO2 reactivity measurements, it is often assumed that the diameter of the large intracranial arteries insonated by transcranial Doppler remains unaffected by changes in arterial CO2 partial pressure. However, the strong cerebral vasodilatory capacity of CO2 challenges this assumption, suggesting that there should be some changes in diameter, even if very small. Data from previous studies on effects of CO2 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 P(CO2) (PET(CO2)) 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 CO2 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(CO2) measurements. In conclusion, the MCA diameter remains constant during small deviations of the PET(CO2) from normocapnia, but increases at higher PET(CO2) values.

KEYWORDS:

MRI; angiography; cerebral blood flow measurement; hypercapnia; hypocapnia; transcranial Doppler

Comment in

PMID:
25190741
DOI:
10.1152/japplphysiol.00651.2014
[Indexed for MEDLINE]
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