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Published on: April 23, 2021
Patients with amnestic mild cognitive impairment have higher cerebrovascular impedance than cognitively normal older
Jun Sugawara1,2,3, Takashi Tarumi1,2,3, Tsubasa Tomoto1,2
1Human Informatics and Interaction Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan.
Abstract:
Brain hypoperfusion is associated with cognitive impairment. Higher cerebrovascular impedance modulus (Z) may contribute to brain hypoperfusion. We tested hypotheses that patients with amnestic mild cognitive impairment (aMCI) (i.e., those who have a high risk of developing Alzheimer's disease) have higher Z than age-matched cognitively normal individuals, and that high Z is correlated with brain hypoperfusion. Fifty-eight patients with aMCI (67 ± 7 yr) and 25 cognitively normal subjects (CN, 65 ± 6 yr) underwent simultaneous measurements of carotid artery pressure (CAP, via applanation tonometry) and middle cerebral arterial blood velocity (CBV, via transcranial Doppler). Z was quantified using cross-spectral and transfer function analyses between dynamic changes in CBV and CAP. Patients with aMCI exhibited higher Z than NC (1.18 ± 0.34 vs. 1.01 ± 0.35 mmHg/cm/s, P = 0.044) in the frequency range from 0.78 to 4.29 Hz. The averaged Z in the frequency range (0.78-3.13 Hz) of high coherence (>0.9) was inversely correlated with total cerebral blood flow measured with 2-D Doppler ultrasonography normalized by the brain tissue mass (via structural MRI) across both patients with aMCI and NC (r = -0.311, P = 0.007), and in patients with aMCI alone (r = -0.306, P = 0.007). Our findings suggest that patients with aMCI have higher cerebrovascular impedance than cognitively normal older adults and that increased cerebrovascular impedance is associated with brain hypoperfusion.NEW & NOTEWORTHY This is the first study to compare cerebrovascular impedance between patients with amnestic mild cognitive impairment (aMCI) and age-matched cognitively normal individuals. Patients with aMCI had higher cerebrovascular impedance modulus than age-matched cognitively normal individuals, which was correlated with brain hypoperfusion. These results suggest the presence of cerebrovascular dysfunction in the dynamic regulation of cerebral blood flow in older adults who have high risks of Alzheimer's disease.
Insights
Patients with amnestic mild cognitive impairment (aMCI) show higher cerebrovascular impedance (Z) than cognitively normal individuals. This increased Z is linked to reduced cerebral blood flow, suggesting cerebrovascular dysfunction in aMCI.
Area of Science:
- Neuroscience
- Cerebrovascular Physiology
- Gerontology
Background:
- Brain hypoperfusion is a known contributor to cognitive impairment.
- Elevated cerebrovascular impedance modulus (Z) is a potential mechanism driving brain hypoperfusion.
- Amnestic mild cognitive impairment (aMCI) represents a high-risk group for Alzheimer's disease development.
Purpose of the Study:
- To investigate if patients with aMCI exhibit higher cerebrovascular impedance (Z) compared to cognitively normal (CN) individuals.
- To determine the correlation between elevated Z and brain hypoperfusion in aMCI patients and CN subjects.
Main Methods:
- Simultaneous measurement of carotid artery pressure (CAP) and middle cerebral arterial blood velocity (CBV) in 58 aMCI patients and 25 CN individuals.
- Quantification of cerebrovascular impedance (Z) using cross-spectral and transfer function analyses.
- Assessment of total cerebral blood flow via 2-D Doppler ultrasonography, normalized by brain tissue mass (structural MRI).
Main Results:
- Patients with aMCI demonstrated significantly higher cerebrovascular impedance modulus (Z) than CN individuals (P=0.044).
- A significant inverse correlation was found between averaged Z (at high coherence frequencies) and normalized total cerebral blood flow across both groups (r=-0.311, P=0.007) and within the aMCI group (r=-0.306, P=0.007).
- These findings indicate that higher cerebrovascular impedance is associated with reduced cerebral blood flow.
Conclusions:
- This study is the first to report higher cerebrovascular impedance in patients with aMCI compared to age-matched cognitively normal individuals.
- Increased cerebrovascular impedance in aMCI patients is correlated with brain hypoperfusion.
- The results suggest underlying cerebrovascular dysfunction in the dynamic regulation of cerebral blood flow in individuals at high risk for Alzheimer's disease.
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