# Assessment of dynamic cerebral blood flow changes during cognitive tasks in patients with post-COVID-19 syndrome

## TL;DR

This study found that patients with post-COVID-19 syndrome have altered blood flow in the brain during cognitive tasks, which may explain their fatigue and cognitive difficulties.

## Contribution

The study introduces a novel method combining sample entropy and coefficient of variation to detect cerebral blood flow changes in post-COVID-19 syndrome.

## Key findings

- Post-COVID-19 syndrome patients showed reduced temporal variability in blood flow during cognitive tasks.
- These patients exhibited increased spatial variability in blood flow compared to controls.
- Altered blood flow patterns correlated with worse cognitive performance and longer reaction times.

## Abstract

The objective of this study was to quantify the variability of cortical blood flow during cognitive load as an indicator of disease-related changes in cerebral capillary blood flow intermittency in patients with post-COVID-19 syndrome. The regulation of cerebral blood flow in the dorsolateral prefrontal cortex under cognitive load was examined using high-resolution functional near-infrared spectroscopy in 36 subjects including 12 patients with post-COVID-19 syndrome and two control groups [12 coronary artery disease patients matched for age and 12 young healthy individuals (CTRL)]. To induce cognitive load, a Flanker task and an N-back task were employed. The structure of temporal variability of local blood flow regulation was assessed using sample entropy at 17 channels spanning both brain hemispheres. The spatial variability of the regional blood flow pattern was evaluated using the coefficient of variation (CV) from sample entropies across all channels. Results revealed a notable discrepancy in that patients with post-COVID-19 syndrome exhibited reduced temporal variability (lower sample entropy) but elevated spatial variability (higher CV) in comparison to coronary artery disease patients during cognitive load (P = 0.02). In the N-back task, the spatial variability increased from healthy individuals to coronary artery disease patients to patients with post-COVID-19 syndrome and was associated with longer reaction time and with lower accuracy. The results confirmed that dynamic cerebral blood flow is altered in patients with post-COVID-19 syndrome, which may be related to fatigue during cognitive tasks. Sample entropy and CV values represent different aspects of blood flow regulation fluctuation. Their simultaneous analysis enabled a meaningful distinction between groups suggesting disease-related changes in brain haemodynamic. The presented method is therefore suitable for describing current states of cortical blood flow regulation and for documenting intervention results in patients with post-COVID-19 syndrome or patients with similar symptoms (e.g. myalgic encephalomyelitis/chronic fatigue syndrome).

Kutz et al. found that post-COVID-19 syndrome patients had altered cerebral blood flow, which was quantified using sample entropy (for temporal variability) and its coefficient of variation (CV) (for spatial variability). The results showed that Post-COVID-19 Syndrome patients had significantly reduced temporal complexity but increased spatial irregularity, which correlated with poorer cognitive performance.

Graphical Abstract