The influence of individual characteristics of the research subject on the electrical conductivity parameters of cerebrospinal fluid

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Background

In forensic medicine, cerebrospinal fluid (CSF) study has been recognized as a promising tool for addressing critical questions in fatal traumatic brain injury (TBI) cases, such as determining the age of the injury and assessing its severity [1–4].

CSF contains biologically active substances that regulate brain functions, neurotrophic support, and neuronal sleep-wake cycles. The electrolyte composition of CSF (including chloride, sodium, potassium, magnesium and iodine) determines its conductive properties [5–7].

Conductometry, the measurement of electrical conductivity in biological fluids, is an objective quantitative method of research, capable of detecting subtle changes with high accuracy. This technique has proven valuable in various areas of medical diagnostics [7–9]. However, the dependence of the conductometric (electroconductive) properties of CSF on several factors that, along with the others, determine the individuality of this biological material remains poorly understood. These factors include the sex and age of the individual from whom the sample was obtained, the cause of death, and the presence or absence of ethanol in the blood and, consequently, in the cerebrospinal fluid at the time of examination.

The limited understanding of these influences restricts the development of conductometric methods for estimating TBI severity and the age of injury. If secondary factors significantly affect CSF electrical conductivity, their influence may obscure the primary determinants of conductivity change — namely, the age and the severity of the injury.

The study aimed to investigate the electrical conductivity properties of CSF in corpses of individuals who died from TBIs, considering individual characteristics of autopsy material, and to evaluate the feasibility of conductometric analysis as a research tool for determination of the age of the injury.

Materials and methods

Study design

This was an experimental, open-label, single-center, cross-sectional, uncontrolled sampling study on the conductometric properties of CSF collected from 124 corpses of individuals aged 17 to 93 years who died from TBIs and its consequences (post-injury intervals ranging from 0 to 10 days). The presence or absence of ethanol in the blood at the time of death was recorded: ethanol was detected in 23 cases (18.5%) and absent in 101 cases (81.5%). The postmortem interval was established through a comprehensive assessment of medical, forensic, and investigative data, ranging from 12.5 to 24 hours.

Eligibility criteria

Inclusion criteria: cases with a confirmed TBI as the immediate cause of death, occurring either in the acute phase or in the delayed period due to post-traumatic complications.

Exclusion criteria: Cases where TBI signs were identified during autopsy in individuals whose cause of death was unrelated to TBI or its consequences.

Study setting

The study was conducted using forensic material from the State Healthcare Institution “Bureau of Forensic Medical Examination of the Yamalo-Nenets Autonomous Area” and the State Healthcare Institution of Perm Territory “Territorial Bureau of Forensic Medical Examination and Pathological Studies”.

Study duration

The research was conducted between 2022 and 2024.

Autopsy sample collection

CSF was collected from each cadaver using a sterile single-use 5.0 mL medical syringe in volumes of 1–2 mL during autopsy while accessing the brain ventricles. To standardize measurement conditions, the syringe was placed in a thermostat at 25оC for temperature stabilization. After 30–45 minutes, CSF was transferred from the syringe into a special cuvette to study its electrical conductivity. Electrical conductivity was measured using an “AKIP RLC 6109” device (Changzhou Eucol Electronic Technology Co. Ltd, China), connected to a computer via an USB interface. The device, registered in the State Register of Measuring Instruments of the Russian Federation (No. 56479-14) and certified for compliance, allows to measure resistance, impedance, capacitance and inductance with a 0.1% error at frequencies of 0.1 kHz, 1 kHz and 10 kHz.

Main study outcome

Electrical conductivity values of cerebrospinal fluid were obtained from corpses of individuals who died from traumatic brain injury and its consequences. All values were determined at three sinusoidal current frequencies (100 Hz, 1 kHz, 10 kHz).

Subgroup analysis

In the course of mathematical analysis, subgroups were sequentially formed according to the possible influence of the factor under study, including the subject’s sex, age, presence of ethanol in the blood at the time of death, absolute ethanol concentration (‰), and postmortem interval (hours).

Methods for registration of outcomes

Electrical conductivity was measured at electric current frequencies of 0.1 kHz, 1 kHz, and 10 kHz by connecting the electrodes of a cuvette filled with CSF with the input contacts of the measuring device (AKIP RLC 6109) and using the standard device settings at the specified frequencies. The results were automatically recorded through computer interface by Microsoft Excel in real time mode.

Ethical review

All research procedures adhered to bioethical principles relevant to biomedical studies. The study was approved by the Bioethics Committee of Izhevsk State Medical Academy, Ministry of Health of Russia, and formally approved by the Scientific Council on August 31, 2022 (Protocol No. 1).

Statistical analysis

Sample size was not pre-calculated.

The following statistical analyses were performed: mean (M), standard deviation (SD), and standard error (m) calculations; comparative intergroup analysis using the Kruskal–Wallis test; correlation analysis using Kendall’s and Spearman’s tests. Data were recorded in a Microsoft Excel database (Microsoft Corporation, USA) and processed using IBM SPSS 23.0 (IBM, USA) following statistical research guidelines recommended for biological and medical studies [10].

Results

Participant characteristics

The study analyzed CSF samples from 124 deceased individuals with confirmed TBI as the direct cause of death, both in the early and late post-traumatic periods (up to 10 days after the injury). To assess the influence of individual characteristics on CSF electrical conductivity, the study population was divided into subgroups based on age, sex, presence of ethanol in the blood, and postmortem interval. The distribution of analyzed samples by sex and age characteristics is presented in Table 1.

 

Table 1. Structure of the studied material with regard to sex and age characteristics of corpses of persons who died from craniocerebral trauma and its consequences

Age, years	Indicator, n
	Men	Women	Total
<20	4	1	5
20–24	6	1	7
25–29	4	5	9
30–34	3	4	7
35–39	7	3	10
40–44	7	5	12
45–49	10	4	14
50–54	9	9	18
55–59	7	4	11
60–64	8	3	11
65–69	5	4	9
70–74	1	2	3
75+	2	6	8
Total	73	51	124

 

Primary Findings

The hypothesis regarding sex-related differences in CSF electrical conductivity was tested, and the results are summarized in Table 2, with the data distribution matrix shown in Fig. 1.

 

Table 2. Electrical conductivity of cerebrospinal fluid taking into account the gender of the corpses of persons who died from traumatic brain injury and its consequences

Sex	Statistical analysis	Electrical conductivity, S/m−1×10−4
		0.1 kHz	1 kHz	10 kHz
Male	M	0.696	0.763	0.792
	SD	0.178	0.066	0.069
	m	0.021	0.008	0.008
	n	73	73	73
Female	M	0.773	0.789	0.749
	m	0.183	0.073	0.082
	SD	0.026	0.010	0.011
	n	51	51	51
Total	M	0.728	0.774	0.775
	m	0.183	0.069	0.077
	SD	0.016	0.006	0.007
	n	124	124	124

 

Fig. 1. Sorted observations of cerebrospinal fluid conductivity by the variable "gender".

 

It was ascertained that differences were recorded between the groups formed on the basis of the sex of the deceased. The results of pairwise comparison between the “male” and “female” groups, conducted using the Kruskal–Wallis test, is presented in Table 3. The comparative study reveals that CSF electrical conductivity value differs between males and females (p <0.05) at frequencies of 0.1 kHz, 1 kHz, and 10 kHz, indicating that sex of the examined subject should be considered a critical factor in conductometric study of his CSF.

 

Table 3. Kruskal–Wallis test for assessing the influence of gender on cerebrospinal fluid conductivity (analysis results in SPSS 23.0)

Frequency, kHz	Kruskal–Wallis Criterion	Significance
0.1	0.026	Significant differences
1.0	0.019	Significant differences
10	0.003	Significant differences

 

The mean CSF conductivity values for the age groups (see Table 1) are presented in Table 4.

 

Table 4. Electrical conductivity of cerebrospinal fluid taking into account the distribution by age groups of corpses of persons who died from traumatic brain injury and its consequences. average (M)

Age Group. years	Electrical conductivity, S/m−1×10−4
	100 kHz	1 kHz	10 kHz
<20	0.580±0.058	0.771±0.028	0.818±0.023
20–24	0.710±0.066	0.771±0.029	0.814±0.018
25–29	0.922±0.021	0.837±0.010	0.743±0.023
30–34	0.750±0.071	0.786±0.022	0.754±0.037
35–39	0.719±0.068	0.758±0.018	0.758±0.036
40–44	0.708±0.051	0.765±0.021	0.781±0.019
45–49	0.732±0.056	0.780±0.023	0.754±0.025
50–54	0.664±0.044	0.748±0.014	0.771±0.019
55–59	0.698±0.053	0.783±0.018	0.794±0.019
60–64	0.724±0.052	0.747±0.020	0.804±0.020
65–69	0.691±0.053	0.768±0.028	0.790±0.025
70–74	0.944±0.006	0.745±0.066	0.764±0.016
75+	0.782±0.060	0.817±0.025	0.742±0.021
Total	0.728±0.016	0.774±0.006	0.775±0.007

 

Visually, no apparent differences were observed between the different age groups. To ensure objective analysis, the Kruskal–Wallis test was applied, with results shown in Table 5.

 

Table 5. Kruskal-Wallis test for assessing the effect of age on cerebrospinal fluid conductivity

Frequency, kHz Kruskal–Wallis	Criterion	Significance
0.1	0.056	No significant differences
1.0	0.183	No significant differences
10	0.299	No significant differences

 

As the presented data show, the electrical conductivity of CSF in corpses at the tested frequencies does not exhibit a dependence on the subject’s age group. However, it should be noted that the conducted analysis has certain limitations, as age is a dynamic characteristic of an individual, and any division into age periods (age groups) is inherently arbitrary. Given this limitation, correlation analysis was deemed the most appropriate approach to determine the relationship between two dynamically changing parameters — age of an individual and CSF electrical conductivity.

Prior to correlation analysis, data distribution within the study groups was found to deviate from a normal distribution. Therefore, nonparametric methods were applied — Kendall’s and Spearman’s correlation analysis. The use of two methods at once should more reliably confirm the presence (or absence) of correlation relations (Table 6).

 

Table 6. Correlation coefficients of age and electrical conductivity cerebrospinal fluid

Correlation analysis	Electrical conductivity, S/m−1×10−4
	100 kHz	1 kHz	10 kHz
Kendall’s Correlation Coefficient	0.031	-0.042	-0.019
Significance	0.619	0.502	0.768
Spearman’s Correlation Coefficient	0.041	-0.058	-0.022
Significance	0.648	0.520	0.807

 

The calculations confirmed that CSF conductivity within the tested frequency range was not correlated with age.

To examine the effect of ethanol consumption prior to death on CSF electrical conductivity, the study population was divided into two groups: “Without Ethanol” (ethanol absent in blood) and “With Ethanol” (ethanol detected in blood). The absolute ethanol concentration (‰) was not considered, as it represents a relative measure [11]. Additionally, only cases without signs of decomposition were included in the study, thereby excluding the possibility of ethanol formation [12]. The mean CSF conductivity values for the two groups are presented in Table 7, demonstrating visible differences at 0.1 kHz and 10 kHz. However, the Kruskal–Wallis test (Table 8) confirmed statistically significant differences between the two groups at all tested frequencies.

 

Table 7. Cerebrospinal fluid conductivity in selected groups. average (M)

Group	Electrical conductivity, S/m−1×10−4
	0.1 kHz	1 kHz	10 kHz
Without ethanol	0.786±0.007	0.683±0.017	0.761±0.007
Ethanol present	0.720±0.015	0.926±0.010	0.831±0.008
Mean	0.775±0.007	0.728±0.016	0.774±0.006

 

Table 8. Kruskal–Wallis test to assess the impact of ethanolemia on the conductivity of cerebrospinal fluid

Frequency, kHz	Kruskal–Wallis Criterion	Significance
0.1	0.001	Significant differences
1.0	0.001	Significant differences
10	0.001	Significant differences

 

This finding raised the question of whether absolute ethanol concentration should also be considered. To test this hypothesis, correlation analysis was conducted using the previously applied coefficients (Table 9). The results indicated that CSF electrical conductivity was not significantly correlated with absolute ethanol concentration (‰) but was significantly affected by the mere presence of ethanol.

 

Table 9. Correlation coefficients between ethanol concentration and conductivity of cerebrospinal fluid

Correlation analysis	Electrical conductivity, S/m−1×10−4
	100 kHz	1 kHz	10 kHz
Kendall’s Correlation Coefficient	0.124	-0.026	-0.038
Significance	0.252	0.813	0.730
Spearman’s Correlation Coefficient	0.166	-0.035	-0.083
Significance	0.265	0.816	0.580

 

Since postmortem interval (PMI) is a dynamic characteristic, correlation analysis is considered to be the most appropriate method to determine the relationship between two changing variables: time since death and CSF electrical conductivity. As previously, the choice was made in favor of nonparametric methods of analysis, the results of which are presented in Table 10. A weak negative correlation (−0.159±0.02) was identified at 0.1 kHz, necessitating additional analysis using one-way analysis of variance (ANOVA) (Table 11). The calculations indicated no statistically significant influence of postmortem interval on CSF conductivity values (p >0.05).

 

Table 10. Results of correlation analysis for conductometry cerebrospinal fluid

Correlation analysis	Electrical conductivity, S/m−1×10−4
	100 kHz	1 kHz	10 kHz
Kendall’s Correlation Coefficient	-0,159*	-0.06	0.05
Significance	0.02	0.41	0.49
Spearman’s Correlation Coefficient	-0,212*	-0.07	0.07
Significance	0.02	0.44	0.45
Note. * Correlation is significant at the 0.05 level.

 

Table 11. Univariate analysis of variance (ANOVA) effects age of death by the amount of electrical conductivity cerebrospinal fluid

Parameters		Sum of squares	df	Mean square	F	p
0.1 kHz	Between groups	0.80	18	0.044	1.39	0.15
	Within groups	3.34	105	0.032	-	-
	Total	4.14	123	-	-	-
1 kHz	Between groups	0.13	18	0.007	1.57	0.08
	Within groups	0.47	105	0.004	-	-
	Total	0.59	123	-	-	-
10 kHz	Between groups	0.11	18	0.006	0.99	0.48
	Within groups	0.62	105	0.006	-	-
	Total	0.73	123	-	-	-

 

Discussion

Summary of the primary study results

The study results demonstrated that the objects contained a sufficient quantity of dissolved ions, which determine the electrical conductivity of CSF. At the same time, objects obtained from corpses of individuals of different sex, age, with or without ethanol in the blood, showed variations in the absolute values of the measured parameter. This necessitated an investigation into the effects of these individual characteristics on cerebrospinal fluid conductivity.

Statistical analysis revealed that sex was a significant factor affecting CSF electrical conductivity, whereas chronological age had no statistically significant influence on the studied properties of autopsy material.

Additionally, while absolute ethanol concentration (‰) did not significantly affect CSF conductivity, the existence of ethanol in the object under study significantly altered its ability to conduct alternating electric current.

Postmortem examinations conducted within the first 24 hours after death did not require adjustments for postmortem interval, as no significant changes in the conductometric properties of CSF occurred within this timeframe.

Discussion of the primary study results

As shown in Tables 2–6, CSF electrical conductivity did not correlate with the subject’s age within the tested frequency range.

According to numerous researchers, ethanol existence in the blood can alter various biophysical and biochemical properties of tissues, organs, and bodily fluids [13], including changes in the trace element and protein composition of blood [14]. These factors may theoretically affect CSF composition and properties. The calculation in Tables 7–9, indicates that the CSF conductivity is not significantly correlated with ethanol concentration (‰), although the existence of ethanol in blood has a notable effect on conductometric measurements.

The postmortem interval (time since death) could potentially influence CSF properties due to ongoing postmortem processes, such as autolysis and decomposition. For this reason, the present study focused exclusively on the first 24 hours postmortem. However, even within the 24-hour postmortem interval, changes in the electrical conductivity properties of CSF may occur as the postmortem interval increases. Based on the results of our study, the absolute time elapsed between death and CSF extraction for conductometric analysis may be disregarded, provided it falls within the studied 24-hour interval.

Adverse events

No adverse events were observed in the course of this study.

Study limitations

When planning and conducting the study, the sample size to achieve the required statistical power of the results was not calculated. Therefore, the sample may not be fully representative, and the findings should not be extrapolated to the general population outside the study.

Conclusion

Conductometric analysis of CSF allows for the reliable detection of changes in CSF properties caused by factors that determine the individual characteristics of the subject from whose corpse it was removed for study.

All changes caused by the mentioned factors must be considered when developing a conductometric analysis methodology for CSF in individuals who died from traumatic brain injury, as they may affect the assessment of injury severity and the age of the injury.

Additional information

Funding source. This study was not supported by any external sources of funding.

Competing interests. The authors declare that they have no competing interests.

Authors’ contribution. All authors made a substantial contribution to the conception of the work, acquisition, analysis, interpretation of data for the work, drafting and revising the work, final approval of the version to be published and agree to be accountable for all aspects of the work. V.V. Agzamov, S.M. Bayandina, M.A. Pozdeeva: data collection; A.Yu. Vavilov, A.R. Pozdeev writing the manuscript; A.Yu. Vavilov, A.R. Pozdeev, S.M. Bayandina: scientific editing of the manuscript; A.Yu. Vavilov, A.R. Pozdeev, S.M. Bayandina, V.V. Agzamov, M.A. Pozdeeva review and approval of the final version of the manuscript.

About the authors

Alexey Yu. Vavilov

Izhevsk State Medical Academy

Email: izhsudmed@hotmail.com
ORCID iD: 0000-0002-9472-7264
SPIN-code: 3275-3730

MD, Dr. Sci. (Medicine), Professor

Россия, Izhevks

Alexey R. Pozdeev

Izhevsk State Medical Academy

Email: apozdeev@bk.ru
ORCID iD: 0000-0002-6302-5219
SPIN-code: 2242-4828

MD, Dr. Sci. (Medicine), Assistant Professor

Россия, Izhevks

Airat А. Khalikov

Bashkir State Medical University

Email: airat.expert@mail.ru
ORCID iD: 0000-0003-1045-5677
SPIN-code: 1895-7300

MD, Dr. Sci. (Medicine), Professor

Россия, Ufa

Sophia M. Bayandina

Izhevsk State Medical Academy

Email: bay_sofia@mail.ru
ORCID iD: 0009-0005-9888-512X
SPIN-code: 8604-6691
Россия, Izhevsk

Vadim V. Agzamov

Bashkir State Medical University

Author for correspondence.
Email: expert.sudmed@yandex.ru
ORCID iD: 0000-0001-9845-2280
SPIN-code: 2601-5485
Россия, Ufa

Maria A. Pozdeyeva

Bauman Moscow State Technical University

Email: mashapozdeeva5@gmail.com
ORCID iD: 0009-0007-6403-9886
SPIN-code: 4731-6769
Россия, Moscow

References

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