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On the assessment of cerebrovascular reactivity using hypercapnia BOLD MRI.

ABSTRACT: Cerebrovascular reactivity (CVR) reflects the capacity of blood vessels to dilate and is an important marker for brain vascular reserve. It may provide a useful addition to the traditional baseline blood flow measurement when assessing vascular factors in brain disorders. Blood-oxygenation-level-dependent MRI under CO(2) inhalation offers a non-invasive and quantitative means to estimate CVR in humans. In this study, we investigated several important methodological aspects of this technique with the goal of optimizing the experimental and data processing strategies for clinical use. Comparing 4 min of 5% CO(2) inhalation (less comfortable) to a 1 min inhalation (more comfortable) duration, it was found that the CVR values were 0.31 +/- 0.05%/mmHg (N = 11) and 0.31 +/- 0.08%/mmHg (N = 9), respectively, showing no significant differences between the two breathing paradigms. Therefore, the 1 min paradigm is recommended for future application studies for patient comfort and tolerability. Furthermore, we have found that end-tidal CO(2) recording was useful for accurate quantification of CVR because it provided both timing and amplitude information regarding the input function to the brain vascular system, which can be subject-dependent. Finally, we show that inter-subject variations in CVR are of physiologic origin and affect the whole brain in a similar fashion. Based on this, it is proposed that relative CVR (normalized against the CVR of the whole brain or a reference tissue) may be a more sensitive biomarker than absolute CVR in clinical applications as it minimizes inter-subject variations. With these technological optimizations, CVR mapping may become a useful method for studies of neurological and psychiatric diseases.

SUBMITTER: Yezhuvath US

PROVIDER: S-EPMC2726998 | biostudies-other | 2009 Aug

REPOSITORIES: biostudies-other

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Project description:Cerebrovascular reactivity (CVR), is important for determining future risk of cerebrovascular disease. It is unclear if primary aging is associated with reductions in CVR because previous studies often include participants with vascular risk factors. Additionally, the inconsistency in the literature may be due to the inherent difficulty in quantifying intracranial cerebral blood flow and CVR. To address these limitations, we determined the effect of age on CVR in the large intracranial vessels in adults with low vascular risk using state-of-the-art MRI techniques. We also determined if the effect of age on CVR was sex-specific. Young (n = 20; 25 ± 3 years) and older (n = 19; 61 ± 5 years) healthy, physically active adults participated in the study. CVR was measured in response to hypercapnia using 4D flow MRI, which allows for simultaneous angiographic and quantitative blood flow measurements in the intracranial arteries. Older adults had lower global CVR and CVR in multiple intracranial arteries [right and left internal carotid arteries (ICA), right and left middle cerebral arteries (MCA), and basilar artery (BA)] compared with young adults (p < 0.05 for all). In addition, the MCA dilated significantly in response to hypercapnia in young (p < 0.05), but not older adults. Young men demonstrated higher global CVR and CVR in multiple intracranial arteries (ICAs, MCAs, and BA) compared with young women and older men (p < 0.05 for both); however, CVR did not differ between young women and older women. Our results demonstrate that, using 4D flow MRI, primary aging is associated with lower CVR in adults with low vascular risk. In addition, the effect of age on CVR may be driven by men. The 4D flow MRI technique may provide a promising new alternative to measure cerebrovascular physiology without the limitations of commonly used techniques. Future studies could utilize this MRI technique to examine interventions to maintain CVR with advancing age. This study was registered under clinicaltrials.gov # NCT02840851.

Project description:BackgroundObstructive sleep apnea and nocturnal oxygen desaturations, which are prevalent in sickle cell disease (SCD) and chronic anemia disorders, have been linked to risks of stroke and silent cerebral infarcts (SCI). Cerebrovascular response to intermittent desaturations has not been well studied and may identify patients at greatest risk.PurposeTo investigate the cerebral dynamic response to induced desaturation in SCD patients with and without SCI, chronic anemia, and healthy subjects.Study typeProspective.SubjectsTwenty-six SCD patients (age = 21 ± 8.2, female 46.2%), including 15 subjects without SCI and nine subjects with SCI, 15 nonsickle anemic patients (age = 22 ± 5.8, female 66.7%), and 31 controls (age = 28 ± 12.3, female 77.4%).Field strength/sequence3T, gradient-echo echo-planar imaging.AssessmentA transient hypoxia challenge of five breaths of 100% nitrogen gas was performed with blood oxygen level-dependent (BOLD) MRI and near-infrared spectroscopy (NIRS) acquisitions. Hypoxia responses were characterized by desaturation depth, time-to-peak, return-to-baseline half-life, and posthypoxia recovery in the BOLD and NIRS time courses. SCI were documented by T2 fluid-attenuation inversion recovery (FLAIR).Statistical testsUnivariate and multivariate regressions were performed between hypoxic parameters and anemia predictors. Voxelwise two-sample t-statistic maps were used to assess the regional difference in hypoxic responses between anemic and control groups.ResultsCompared to controls, SCD and chronically anemic patients demonstrated significantly higher desaturation depth (P < 0.01) and shorter return-to-baseline timing response (P < 0.01). Patients having SCI had shorter time-to-peak (P < 0.01), return-to-baseline (P < 0.01), and larger desaturation depth (P < 0.01) in both white matter regions at risk and normal-appearing white matter than patients without infarcts. On multivariate analysis, desaturation depth and timing varied with age, sex, blood flow, white blood cells, and cell-free hemoglobin (r2 = 0.25 for desaturation depth; r2 = 0.18 for time-to-peak; r2 = 0.37 for return-to-baseline).Data conclusionTransient hypoxia revealed global and regional response differences between anemic and healthy subjects. SCI was associated with extensive heterogeneity of desaturation dynamics, consistent with extensive underlying microvascular remodeling.

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On the assessment of cerebrovascular reactivity using hypercapnia BOLD MRI.

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