Results

The study population consisted of 29 deceased individuals examined over a wide and heterogeneous postmortem interval, allowing evaluation of bioelectrical parameter behavior across different postmortem phases. The postmortem interval ranged from 1.60 to 192.87 h, with a mean value of 38.67 h. The distribution of PMI values was markedly right-skewed, with a higher concentration of cases within the first 48 h after death and a smaller number of subjects examined at longer intervals. This distribution reflects routine forensic casework and allowed exploratory evaluation across different postmortem phases.

Body mass index values showed substantial inter-individual variability, ranging from 9.87 to 57.03 kg/m², with a mean BMI of 26.02 kg/m². The sample therefore included individuals across the full spectrum of nutritional status, from severely underweight to morbidly obese. BMI values were not clustered within specific PMI ranges, and no systematic association between body habitus and time since death was observed at a descriptive level.

Pre-autopsy bioelectrical impedance analysis revealed wide dispersion across all measured electrical parameters. Resistance values ranged from 105.5 to 1053 ohms, with a mean value of 464.77 ohms, indicating pronounced variability in tissue conductive properties among cases. Reactance ranged from 26.9 to 256.9 ohms, with a mean of 83.79 ohms, reflecting heterogeneity in tissue capacitive behavior. Impedance values closely mirrored resistance, ranging from 110.6 to 1073 ohms, with a mean of 472.54 ohms. Phase angle values demonstrated the broadest relative distribution, ranging from 3.3 to 22.4 degrees, with a mean value of 11.24 degrees. The dispersion of phase angle values was evident across the entire PMI range, suggesting that this parameter is influenced by both postmortem temporal factors and inter-individual variability.

Correlation analysis identified distinct relationships between PMI and the evaluated bioelectrical parameters. Phase angle demonstrated a moderate positive association with PMI, with a Pearson correlation coefficient of r = + 0.46 (p = 0.012). The association remained significant when assessed using Spearman’s rank correlation analysis (ρ = +0.58, p = 0.001), indicating persistence of the relationship despite the non-normal distribution of PMI values. Despite considerable variability, phase angle values tended to increase with increasing postmortem interval, although the association remained highly heterogeneous across cases. Reactance showed a weak positive Pearson correlation with PMI (r = + 0.25, p = 0.183), whereas Spearman analysis demonstrated a stronger monotonic association (ρ = +0.52, p = 0.004). Resistance, impedance, and BMI showed no statistically significant associations with PMI in either Pearson or Spearman analyses. In contrast, resistance and impedance showed no meaningful correlation with PMI, with correlation coefficients of r = − 0.07 and r = − 0.05, respectively, indicating that these parameters were largely independent of postmortem time within the studied interval.

The potential influence of body mass index on postmortem electrical behavior was explored by examining the relationship between BMI and PMI. No significant correlation was identified between these variables, although a weak negative trend was observed (r = − 0.20).

To further characterize the temporal behavior of phase angle, exploratory regression modeling was performed. A simple linear regression model describing phase angle as a function of PMI demonstrated a positive slope, but with limited explanatory power, accounting for approximately 21% of the observed variance (R² ≈ 0.21). Visual inspection of the data suggested that the relationship between phase angle and PMI was not optimally captured on a linear time scale, particularly at longer PMIs. When PMI was logarithmically transformed, the relationship was better described by a log-linear model, in which phase angle was expressed as a function of the natural logarithm of PMI according to the equation PA = 6.14 + 2.12 · ln(PMI). This model accounted for approximately 38% of the observed variance in phase angle values (R² ≈ 0.38), representing a substantial improvement over the linear model. The regression coefficient for ln(PMI) was statistically significant (p < 0.001), indicating a indicating a potential association between increasing postmortem interval and higher phase angle values. Nevertheless, residual dispersion remained considerable, with a root mean square error of approximately 4.6 degrees, reflecting marked inter-individual variability and limiting the predictive accuracy of the model at the individual case level.

A subgroup analysis was conducted in ten cases for which bioelectrical measurements were obtained both before and after completion of the forensic autopsy. In all examined cases, phase angle values increased following autopsy when compared with pre-autopsy measurements. This increase was observed regardless of PMI duration or BMI category and appeared to be a systematic effect rather than random measurement variability. In contrast, resistance, reactance, and impedance values demonstrated heterogeneous changes after autopsy, with no consistent directional pattern across cases. These findings indicate that invasive postmortem procedures exert a significant influence on phase angle measurements, likely through anatomical disruption, loss of compartmental integrity, and redistribution of fluids.

Taken together, these results indicate that among the evaluated bioelectrical parameters, phase angle shows the most consistent and informative relationship with postmortem interval and follows a time-dependent trend more appropriately described on a logarithmic scale. However, the magnitude of residual variability, the overlap between PMI ranges, and the influence of autopsy-related changes underscore the exploratory nature of these findings and highlight the limitations of using phase angle as a standalone estimator of postmortem interval (Tables 1 and 2).

Variable | Value
Number of cases | 29
Sex | Both sexes
Age (years), range | Adult population
Postmortem interval (hours), range | 1.60–192.87
Postmortem interval (hours), mean | 38.67
Body mass index (kg/m²), range | 9.87–57.03
Body mass index (kg/m²), mean | 26.02
Autopsied cases, n (%) | 13 (44.8%)
Non-autopsied cases, n (%) | 16 (55.2%)
Cases with pre- and post-autopsy BIA | 10

Parameter | Mean | Range
Resistance (Ω) | 464.77 | 105.5–1053
Reactance (Ω) | 83.79 | 26.9–256.9
Impedance (Ω) | 472.54 | 110.6–1073
Phase angle (°) | 11.24 | 3.3–22.4

All measurements were obtained prior to any invasive postmortem procedure (Tables 3 and 4).

Variable | Pearson’s r | p value | Spearman’s ρ | p value
Resistance | −0.07 | 0.719 | −0.002 | 0.991
Reactance | + 0.25 | 0.183 | + 0.52 | 0.004
Impedance | −0.05 | 0.778 | + 0.03 | 0.893
Phase angle | + 0.46 | 0.012 | + 0.58 | 0.001
Body mass index | −0.20 | 0.289 | −0.22 | 0.248

Model | Regression equation | R²
Linear | PA = 9.29 + 0.050 · PMI | ≈ 0.21
Log-linear | PA = 6.14 + 2.12 · ln(PMI) | ≈ 0.38