The ability to determine asphyxia as a cause of death
is important
in forensic practice and helps us to judge whether a case is criminal.
However, in some cases where the deceased has underlying heart disease,
death by asphyxia cannot be determined by traditional autopsy and
morphological observation under a microscope because there are no
specific morphological features for either asphyxia or sudden cardiac
death (SCD). Here, Fourier transform infrared (FTIR) spectroscopy
was employed to distinguish asphyxia from SCD. A total of 40 lung
tissues (collected at 0 h and 24 h postmortem) from 20 rats (10 died
from asphyxia and 10 died from SCD) and 16 human lung tissues from
16 real cases were used for spectral data acquisition. After data
preprocessing, 2675 spectra from rat lung tissues and 1526 spectra
from human lung tissues were obtained for subsequent analysis. First,
we found that there were biochemical differences in the rat lung tissues
between the two causes of death by principal component analysis and
partial least-squares discriminant analysis (PLS-DA), which were related
to alterations in lipids, proteins, and nucleic acids. In addition,
a PLS-DA classification model can be built to distinguish asphyxia
from SCD. Second, based on the spectral data obtained from lung tissues
allowed to decompose for 24 h, we could still distinguish asphyxia
from SCD even when decomposition occurred in animal models. Nine important
spectral features that contributed to the discrimination in the animal
experiment were selected and further analyzed. Third, 7 of the 9 differential
spectral features were also found to be significantly different in
human lung tissues from 16 real cases. A support vector machine model
was finally built by using the seven variables to distinguish asphyxia
from SCD in the human samples. Compared with the linear PLS-DA model,
its accuracy was significantly improved to 0.798, and the correct
rate of determining the cause of death was 100%. This study shows
the application potential of FTIR spectroscopy for exploring the subtle
biochemical differences resulting from different death processes and
determining the cause of death even after decomposition.