The severity of microstrokes depends on local vascular topology and baseline perfusion

Cortical microinfarcts are linked to pathologies like cerebral amyloid angiopathy and dementia. Despite their relevance for disease progression, microinfarcts often remain undetected and the smallest scale of blood flow disturbance has not yet been identified. We employed blood flow simulations in realistic microvascular networks from the mouse cortex to quantify the impact of single-capillary occlusions. Our simulations reveal that the severity of a microstroke is strongly affected by the local vascular topology and the baseline flow rate in the occluded capillary. The largest changes in perfusion are observed in capillaries with two inflows and two outflows. This specific topological configuration only occurs with a frequency of 8%. The majority of capillaries have one inflow and one outflow and is likely designed to efficiently supply oxygen and nutrients. Taken together, microstrokes bear potential to induce a cascade of local disturbances in the surrounding tissue, which might accumulate and impair energy supply locally.


Sample-size estimation
• You should state whether an appropriate sample size was computed when the study was being designed • You should state the statistical method of sample size computation and any required assumptions • If no explicit power analysis was used, you should describe how you decided what sample (replicate) size (number) to use Please outline where this information can be found within the submission (e.g., sections or figure legends), or explain why this information doesn't apply to your submission:

Replicates
• You should report how often each experiment was performed • You should include a definition of biological versus technical replication • The data obtained should be provided and sufficient information should be provided to indicate the number of independent biological and/or technical replicates • If you encountered any outliers, you should describe how these were handled • Criteria for exclusion/inclusion of data should be clearly stated • High-throughput sequence data should be uploaded before submission, with a private link No power analysis was used to estimate the sample size. To further comment on the sample size it should be distinguished between analyses focusing on 1) the entire capillary bed and 2) the comparison of microstroke cases.
-1) Investigations focusing on the entire capillary bed: The microvascular networks contain several thousand capillaries, i.e. the sample size is very large and allows conclusion on general characteristics of the capillary bed. The precise sample size is given in the figure legends. -2) Comparison of microstroke cases: We chose >= 12 different microstroke capillaries as sample size for one microstroke case and >=20 microstroke capillaries for the most relevant cases.
Here, the sample size is a compromise between total computational cost and observable differences between cases with different topological configurations or further factors influencing the severity of a microstroke. It is important to note that even if the sample size per microstroke case is >=12 the total number of capillaries analyzed per case is significantly larger. This is because we also consider capillaries up to five generations apart from the microstroke capillary and within an analysis box of > 200,000 µm 3 .
for reviewers provided (these are available from both GEO and ArrayExpress) Please outline where this information can be found within the submission (e.g., sections or figure legends), or explain why this information doesn't apply to your submission:

Statistical reporting
• Statistical analysis methods should be described and justified • Raw data should be presented in figures whenever informative to do so (typically when N per group is less than 10) • For each experiment, you should identify the statistical tests used, exact values of N, definitions of center, methods of multiple test correction, and dispersion and precision measures (e.g., mean, median, SD, SEM, confidence intervals; and, for the major substantive results, a measure of effect size (e.g., Pearson's r, Cohen's d) • Report exact p-values wherever possible alongside the summary statistics and 95% confidence intervals. These should be reported for all key questions and not only when the p-value is less than 0.05.
Please outline where this information can be found within the submission (e.g., sections or figure legends), or explain why this information doesn't apply to your submission: (For large datasets, or papers with a very large number of statistical tests, you may upload a single table file with tests, Ns, etc., with reference to sections in the manuscript.)

Group allocation
• Indicate how samples were allocated into experimental groups (in the case of clinical studies, please specify allocation to treatment method); if randomization was used, please also state if restricted randomization was applied • Indicate if masking was used during group allocation, data collection and/or data analysis -The need to perform replicates does not apply for our study. The timeaveraged simulation results are deterministic such that replicates are not necessary. -The selection criteria for capillaries considered in the study is described in 5.
Methods -Within the figures we provide the raw data for each microstroke simulation. Whenever possible, we also provide the raw data for individual capillaries. -To conclude that changes in flow rate between the baseline and the stroke scenario are significant, we analyze the baseline fluctuations of the flow field and derive a robust criterion for the relative change in flow rate. The approach is described in 5.Methods à5 Please outline where this information can be found within the submission (e.g., sections or figure legends), or explain why this information doesn't apply to your submission: Additional data files ("source data") • We encourage you to upload relevant additional data files, such as numerical data that are represented as a graph in a figure, or as a summary table • Where provided, these should be in the most useful format, and they can be uploaded as "Source data" files linked to a main figure or table • Include model definition files including the full list of parameters used • Include code used for data analysis (e.g., R, MatLab) • Avoid stating that data files are "available upon request" Please indicate the figures or tables for which source data files have been provided: For analysis purposes individual capillaries were assigned to different group (e.g. based on baseline flow rate). The precise criteria are described in 5. Methods à 5.2 Microstroke simulations and summarized in Supplementary File 1a.
We did not yet upload any source files. However, we would like to upload the timeaveraged simulations results including analysis scripts upon acceptance of our manuscript.