Mean Arterial Pressure and Cerebral Hemodynamics Across The Lifespan: A Cross-Sectional Study From Human Connectome Project-Aging

Abstract

Background: Cerebral perfusion is directly affected by systemic blood pressure, which has been shown to be negatively correlated with cerebral blood flow (CBF). The impact of aging on these effects is not fully understood.

Purpose: To determine whether the relationship between mean arterial pressure (MAP) and cerebral hemodynamics persists throughout the lifespan.

Study type: Retrospective, cross-sectional study.

Population: Six hundred and sixty-nine participants from the Human Connectome Project-Aging ranging between 36 and 100+ years and without a major neurological disorder.

Field strength/sequence: Imaging data was acquired at 3.0 Tesla using a 32-channel head coil. CBF and arterial transit time (ATT) were measured by multi-delay pseudo-continuous arterial spin labeling.

Assessment: The relationships between cerebral hemodynamic parameters and MAP were evaluated globally in gray and white matter and regionally using surface-based analysis in the whole group, separately within different age groups (young: <60 years; younger-old: 60-79 years; oldest-old: ≥80 years).

Statistical tests: Chi-squared, Kruskal-Wallis, ANOVA, Spearman rank correlation and linear regression models. The general linear model setup in FreeSurfer was used for surface-based analyses. P < 0.05 was considered significant.

Results: Globally, there was a significant negative correlation between MAP and CBF in both gray (ρ = -0.275) and white matter (ρ = -0.117). This association was most prominent in the younger-old [gray matter CBF (β = -0.271); white matter CBF (β = -0.241)]. In surface-based analyses, CBF exhibited a widespread significant negative association with MAP throughout the brain, whereas a limited number of regions showed significant prolongation in ATT with higher MAP. The associations between regional CBF and MAP in the younger-old showed a different topographic pattern in comparison to young subjects.

Data conclusion: These observations further emphasize the importance of cardiovascular health in mid-to-late adulthood for healthy brain aging. The differences in the topographic pattern with aging indicate a spatially heterogeneous relationship between high blood pressure and CBF.

Level of evidence: 3 TECHNICAL EFFICACY STAGE: 3.

Keywords: aging; arterial spin labeling; arterial transit time; cerebral blood flow; mean arterial pressure.

Figure 1:. The relationship between MAP and cerebral hemodynamics in the whole sample.

Elevated MAP is inversely correlated with CBF and positively correlated with ATT in all age groups. The relationship with CBF is more prominent in the gray matter (A) compared to that in the white matter (B). GM CBF decreases 0.3 ml/100 g/min for each 1 mmHg increase in MAP, whereas this decrease is 0.06 ml/100 g/min per 1 mmHg MAP increase in white matter. A similar yet minor difference is seen between gray matter ATT (0.003 seconds per mmHg increase) (C) and white matter ATT (0.002 seconds per mmHg increase) (D). The shaded areas represent the 95% CI of the regression line.

Figure 2:. Vertex-wise analyses between MAP, CBF and ATT with and without adjustment for age.

Age-unadjusted associations between MAP and hemodynamic parameters display a widespread relationship (top row). After controlling for age effects (bottom row), this pattern mostly endured for CBF compared to ATT. Color bars indicate p-values and the direction of correlation; blue represents a negative correlation whereas red/yellow represents a positive correlation. CBF, Cerebral blood flow; ATT, Arterial transit time; MAP, Mean arterial pressure.

Figure 3:. Vertex-wise comparative group analyses between MAP and CBF.

The relationship between CBF and MAP displayed a significant difference only in a limited number of regions among the oldest-old and younger-old groups (A). Surface-based analyses among the younger-old and young groups highlighted various anatomic regions with more negative slopes in the younger-old with respect to the relationship between MAP and CBF (B). Color bars indicate p values and the direction of the association, with blue representing a more negative slope. CBF, Cerebral blood flow; ATT, Arterial transit time; MAP, Mean arterial pressure.