A Way to Measure Failure to Deliver Sufficient Oxygen and Nutrients to the Aging Brain
The aged vasculature is diminished in its ability to deliver blood to tissues via a range of different mechanisms and their consequences. Capillary density is lost, and the heart weakens, for example. This affects the ability to supply nutrients and oxygen to energy hungry tissues such as the brain, and this in turn affects function. The balance of supply and demand in the brain is not a steady state situation, however. It is complex, just like everything else in the body. Researchers here find a way to measure the degree to which this dynamic, complex balance becomes disrupted with age, thereby contributing to dysfunction.
A healthy brain requires sufficient supplies of glucose and oxygen to function properly, and any impairment of the vasculature will affect their delivery to the target cells. The brain and cardiovascular system work closely together in a common endeavour to match energy supply to demand. Their intimate relationship is reflected in the concept of the neurovascular unit (NVU), corresponding to consideration of the neurons, astrocytes, microglia, pericytes, endothelial cells, and basement membrane as a single functioning entity.
The risk of neurodegenerative disorders increases with age, due to reduced vascular nutrition and impaired neural function. However, the interactions between cardiovascular dynamics and neural activity, and how these interactions evolve in healthy aging, are not well understood. Here, the interactions are studied by assessment of the phase coherence between spontaneous oscillations in cerebral oxygenation measured by functional near-infrared spectroscopy (fNIRS), the electrical activity of the brain measured by EEG, and cardiovascular functions extracted from ECG and respiration effort, all simultaneously recorded.
Signals measured at rest in 21 younger participants (31.1 ± 6.9 years) and 24 older participants (64.9 ± 6.9 years) were analysed by wavelet transform, wavelet phase coherence, and ridge extraction for frequencies between 0.007 and 4 Hz. Coherence between the neural and oxygenation oscillations at ∼ 0.1 Hz is significantly reduced in the older adults. This reduction in coherence indicates that neurovascular interactions change with age. The approach presented promises a noninvasive means of evaluating the efficiency of the neurovascular unit in aging and disease.