Cross wavelet analysis of cerebral hemodynamics in young and older adults

Spontaneous slowoscillations occur in cerebral hemodynamics and blood pressure (BP), and may reflect neurogenic, metabolic ormyogenic control of the cerebral vasculature. Aging is accompanied by a degeneration of the vascular system,which may have consequences for regional cerebral blood flow and cognitive performance. This degeneration may be reflected in a reduction of spontaneous slowoscillations of cerebral hemodynamics and BP. Therefore, we aimed to establish the dependency of slow oscillations of cerebral hemodynamics and BP on the factors age and cognitive load, by using functional near-infrared spectroscopy (fNIRS). Fourteen healthy young (23-32 years) and 14 healthy older adults (64-78 years) performed a verbal n-backworking-memory task. Oxygenated and deoxygenated hemoglobin concentration changes were registered by two fNIRS channels located over left and right prefrontal cortex. BP was measured in the finger by photoplethysmography. We found that very-low-frequency oscillations (0.02-0.07 Hz) and low-frequency oscillations (0.07-0.2 Hz) of cerebral hemodynamics and BP were reduced in the older adults compared to the young during task performance. In young adults, very-low-frequency oscillations of cerebral hemodynamics and BP reduced with increased cognitive load. Cognitive load did not affect low-frequency oscillations of the cerebral hemodynamics and BP. Transfer function analysis indicated that the relationship between BP and cerebral hemodynamic oscillations does not change under influence of age and cognitive load. Our results suggest aging-related changes in the microvasculature such as declined spontaneous activity inmicrovascular smoothmuscle cells and vessel stiffness.Moreover, our results indicate that in addition to local vasoregulatory processes, systemic processes also influence cerebral hemodynamic signals. It is therefore crucial to take the factors age and BP into consideration for the analysis and interpretation of hemodynamic neuroimaging data.;This study aims to assess the relationship between spontaneous oscillations in changes in cerebral tissue oxyhemoglobin concentrations (Delta [HbO2]) and arterial blood pressure (ABP) signals in healthy elderly subjects during the resting state usingwavelet coherence analysis. Continuous recordings of near-infrared spectroscopy (NIRS) and ABP signals were obtained from simultaneous measurements in 33 healthy elderly subjects (age: 70.7 +/- 7.9 years) and 27 young subjects (age: 25.2 +/- 3.7 years) during the resting state. In elderly subjects, the Delta [HbO2] and ABP oscillations were significantly wavelet coherent in interval I, and wavelet phase coherent in intervals I, II and IV. The difference in the wavelet coherence of the elderly subjects and the young subjects indicates an altered cerebral autoregulation caused by aging. This study provides new insight into the dynamics of Delta [HbO2] and ABP oscillations and may be useful in identifying the risk for dynamic cerebral autoregulation processes.