Age-related changes in brain hemodynamics; A calibrated MRI study

Area of Science:

• Neuroimaging
• Physiology
• Gerontology

Background:

• Blood oxygenation-level dependent (BOLD) MRI is used to study age-related changes in neuronal activity.
• Inconsistent findings are often attributed to variations in cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO2).

Purpose of the Study:

• To investigate the impact of aging on baseline CBF and CMRO2.
• To clarify the role of physiological parameters in age-related BOLD signal changes.

Main Methods:

• Studied 20 young and 45 older adults using dual-echo pseudocontinuous arterial spin labeling (ASL).
• Applied normocapnic, hypercapnic, and hyperoxic breathing challenges.
• Calculated whole brain and regional gray matter CBF, ASL cerebrovascular reactivity (CVR), BOLD CVR, oxygen extraction fraction (OEF), and CMRO2.

Main Results:

• Whole brain CBF was significantly lower in older adults (40 ± 9 ml/100 g/min) compared to younger adults (49 ± 14 ml/100 g/min).
• Age-related CBF differences became non-significant when accounting for end-tidal CO2 (EtCO2).
• Whole brain CMRO2 was significantly lower in older adults (133 ± 43 µmol/100 g/min) versus younger adults (181 ± 60 µmol/100 g/min).

Conclusions:

• Age-related CBF variations may be influenced by differences in EtCO2.
• Older individuals exhibit reduced regional CMRO2.
• Future BOLD studies on aging should consider these physiological differences.