Area of origin analysis for expirated patterns using HemoVision

Although bloodstain pattern analysis (BPA) can be performed on various types of patterns, there is a lack of research looking into whether the area of origin (AO) can be determined for expirated patterns. Expirated patterns are formed when blood is pushed out of an opening in the body by the force of air, in some cases forming a pattern of radiating bloodstains which can be analyzed similarly to impact patterns. This research aims to compare the true versus observed AO of expirated patterns using a mechanical rig. In addition, a series of blind expirated patterns was created by human participants. The resultant patterns were analyzed in HemoVision to deduce the AO and determine what kinds of errors manifest. Using the rig, five expirated patterns were produced from 20 cm and 40 cm from a target, at 90° and 45° towards the wall (n = 20). The errors in each direction (X, Y, Z) were assessed. One-sample t-tests of the 3D coordinates found statistically significant differences between the sampled and hypothesized mean (μ = 0) at 90° and 20 cm (x = 11.89, p = 7.220E-04), 90° and 40 cm (x = 22.54, p = 5.764E-06), 45° and 20 cm (x = 13.41, p = 9.888E-04), and 45° and 40 cm (x = 28.16, p = 4.040E-05). This indicates that the AO may not be accurately calculated for expirated patterns, with the largest difference being the distance from the wall. This suggests a unique limitation compared to impact patterns, which tend to have the greatest errors in height. Blind tests were also analyzed to determine the quality of AO analysis using samples from human participants (n = 11).