Crime scene investigation III: Exploring the effects of drugs of abuse and neurotransmitters on Bloodstain Pattern Analysis

The possible misinterpretation of Bloodstain Pattern Analysis (BPA) is explored with regards to the variability in blood viscosity and surface tension values that may result from the presence of a variety of chemical additives, such as cocaine and its prominent metabolite benzoylecgonine hydrate in addition to frequently encountered neurotransmitters, namely dopamine, serotonin and epinephrine. Defibrinated horse blood was spiked with the chemicals of interest over appropriate concentration ranges and subsequent viscosity and surface tension measurements were both conducted utilising a capillary tube viscometer and a tensiometer. In the case of cocaine and its metabolite, concentrations of which encompassed therapeutic to potentially fatal levels, 10⁻⁶ to 10⁻⁴ M respectively, were employed and found to result in an alteration in the dynamic viscosity of defibrinated horse blood of between 1.1 to 7.8% (±0.72 and ±0.77, N = 3) and 6.4 to 9.5% (±0.78 and ±1.52, N = 3) respectively. Furthermore with the addition of variable concentrations of cocaine or its metabolite the surface tension of defibrinated horse blood was found to deviate from that of its unadulterated value of 51.0 mN m⁻¹ (±0.92, N = 3) where for the highest concentration explored a decreased value of either 43.8 or 44.2 mN m⁻¹ (±0.47 and ±0.77, N = 3) was measured respectively. Interestingly, in the case of the neurotransmitters, spiked into defibrinated horse blood over the range of 10⁻⁶ to 10⁻³ M, we find there to be no change or significant deviation in the respective viscosity values measured with regards to that of the unmodified blood. A possible explanation for this differing behaviour is given and where alterations in the viscosity and surface tension values of blood are noted we incorporate such variables into applicable BPA equations in order to ascertain the implications that this may induce within the Forensic interpretation of bloodstains. Consequently, through probing these equations and the employment of bloodstain spatter experiments (commonly employed within BPA) it is found that the addition of drugs of abuse and the presence of common neurotransmitters have no significant implications towards the misinterpretation of BPA.