Cerebral and systemic physiological effects of wearing face masks in young adults.

The COVID-19 pandemic led to widespread mandates requiring the wearing of face masks, which led to debates on their benefits and possible adverse effects. To that end, the physiological effects at the systemic and at the brain level are of interest. We have investigated the effect of commonly available face masks (FFP2 and surgical) on cerebral hemodynamics and oxygenation, particularly microvascular cerebral blood flow (CBF) and blood/tissue oxygen saturation (StO2), measured by transcranial hybrid near-infrared spectroscopies and on systemic physiology in 13 healthy adults (ages: 23 to 33 y). The results indicate small but significant changes in cerebral hemodynamics while wearing a mask. However, these changes are comparable to those of daily life activities. This platform and the protocol provides the basis for large or targeted studies of the effects of mask wearing in different populations and while performing critical tasks.

Comprehensive workflow and its validation for simulating diffuse speckle statistics for optical blood flow measurements.

Diffuse optical methods including speckle contrast optical spectroscopy and tomography (SCOS and SCOT), use speckle contrast (κ) to measure deep blood flow. In order to design practical systems, parameters such as signal-to-noise ratio (SNR) and the effects of limited sampling of statistical quantities, should be considered. To that end, we have developed a method for simulating speckle contrast signals including effects of detector noise. The method was validated experimentally, and the simulations were used to study the effects of physical and experimental parameters on the accuracy and precision of κ. These results revealed that systematic detector effects resulted in decreased accuracy and precision of κ in the regime of low detected signals. The method can provide guidelines for the design and usage of SCOS and/or SCOT instruments.

Dual-task related frontal cerebral blood flow changes in older adults with mild cognitive impairment: A functional diffuse correlation spectroscopy study.

Introduction: In a worldwide aging population with a high prevalence of motor and cognitive impairment, it is paramount to improve knowledge about underlying mechanisms of motor and cognitive function and their interplay in the aging processes. Methods: We measured prefrontal cerebral blood flow (CBF) using functional diffuse correlation spectroscopy during motor and dual-task. We aimed to compare CBF changes among 49 older adults with and without mild cognitive impairment (MCI) during a dual-task paradigm (normal walk, 2- forward count walk, 3-backward count walk, obstacle negotiation, and heel tapping). Participants with MCI walked slower during the normal walk and obstacle negotiation compared to participants with normal cognition (NC), while gait speed during counting conditions was not different between the groups, therefore the dual-task cost was higher for participants with NC. We built a linear mixed effects model with CBF measures from the right and left prefrontal cortex. Results: MCI (n = 34) showed a higher increase in CBF from the normal walk to the 2-forward count walk (estimate = 0.34, 95% CI [0.02, 0.66], p = 0.03) compared to participants with NC, related to a right- sided activation. Both groups showed a higher CBF during the 3-backward count walk compared to the normal walk, while only among MCI, CFB was higher during the 2-forward count walk. Discussion: Our findings suggest a differential prefrontal hemodynamic pattern in older adults with MCI compared to their NC counterparts during the dual-task performance, possibly as a response to increasing attentional demand.