Development of a quantitatively controlled expirated bloodstain generation system using an anatomically-informed oral...

Expirated bloodstains are generated when blood is forcibly expelled from the mouth or upper airway due to air pressure. These patterns often contain biological constituents such as mucus and salivary enzymes, as well as distinctive morphological elements like bubble rings or beaded stains. However, their overall appearance can closely resemble that of impact or cast-off stains, which may lead to potential misinterpretation during forensic analysis. Conventional methods for reproducing expirated stains often rely on human subjects forcibly projecting blood or artificial substitutes, which pose limitations in terms of reproducibility, biosafety, and quantitative control. To address these challenges, this study presents the development of a bloodstain generation system capable of simulating expirated patterns under controlled airflow conditions. The system integrates anatomically informed 3D-printed oral models that simulate either blowing or coughing, combined with a calibrated airflow control unit and artificial blood formulated to match human rheological properties. This configuration enables precise modulation of airflow velocity and oral opening, allowing for consistent generation of expirated bloodstains. Morphological analysis was performed to quantify the area, impact angle, and orientation of stains produced under each condition. The results confirm the system's ability to generate distinct patterns corresponding to different expiratory scenarios. This system provides a safe, reproducible, and quantifiable method for generating expirated bloodstains, offering significant utility in forensic training, as well as in generating machine learning and deep learning datasets for automated classification of bloodstain types.