Postmortem lung weight in drownings: a comparison with acute asphyxiation and cardiac death

1. Introduction 

Although drowning is included in the very common causes of death in accidents and suicides, it may be also a result of violence in concealed homicides [1], [2], [3], [4], [5], [6], [7], [8]. However, the diagnosis of drowning remains one of the most difficult tasks for a forensic pathologist, because a variety of fatal mechanisms may be involved in immersion death, such as hypoxia from water aspiration, laryngeal spasm, fluid and electrolyte disturbances and hypothermia [1], [2], [9], [10], and specific pathomorphological findings for the positive diagnosis often may be poor [10], [11]. There have been a considerable number of studies to investigate ancillary procedures in the diagnosis of drowning, which include classical diatome analysis, histopathology, chemical analyses of blood electrolytes and minerals for the markers of water aspiration [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27] and of surfactants and blood nitrogenous compounds for the markers of pulmonary damage, hemodilution and hypoxia [10], [28], [29], [30]. In macromorphology, froth in the airways and overinflated heavy lungs with a substantial amount of pleural effusion are of significance [1], [2], [10], [11], [31], [32]. A difference in the increased amount of pleural effusion between freshwater and saltwater drownings has also been reported [10], [11]. However, some experts may believe, from their own private experience, that such findings cannot be a marker of drowning. There were also several controversial findings and arguments about the lung weight difference due to the immersion medium [10], [32] and poor knowledge is available about the difference between wet, dry drownings and the related causes of death such as asphyxiation and acute cardiac death.

In the present study, we statistically examined the difference in the lung weight and the amount of pleural effusion between freshwater and saltwater drownings, in comparison with asphyxiation and acute cardiac death, in relation to the gender and age to investigate possible factors involved in the varied mechanisms of death by drowning.

2. Materials and methods 

2.1. Materials 

Autopsy cases of freshwater and saltwater drownings (n=70 and n=75, respectively), asphyxiation (n=85: hanging, n=18; strangulation, n=31; smothering, n=6; aspiration, n=23; others, n=7) and acute cardiac death without immersion in water (n=82) at our institutes during 5 recent years were reviewed, excluding children under the age of 16 years, subjects with some other traumas or diseases which may have modified the dying process and those that had undergone advanced decomposition. Drowning cases with clear circumstantial evidence including the immersion medium were collected, and deaths in bathtubs were not included. These cases included 194 males and 118 females of 20–92 (mean 58.0) years of age (postmortem interval 4.5 h to 8 days). The analyzed parameters were the age, gender, height, weight and estimated postmortem period (time from death to autopsy), immersion media in drownings, lung weight, amount of pleural effusion, heart weight, blood alcohol and drug levels. These findings of the cases are summarized in Table 1. In drowning, water temperature, immersion depth and period were not considered, because these factors were uncertain due to obscure circumstantial evidence in most cases. Autopsy was performed 4–24 h after recovery from water.

Table 1. Case profiles of fatal drowning, asphyxiation and acute cardiac death

Mean values are given in parentheses.

2.2. Statistical analyses 

The Fisher exact test was used to compare two parameters. Comparisons between groups were performed using Student's t-test. The Logistic regression test was used in the multivariate analyses. A P value of less than 0.05 was considered statistically significant. In Fig. 1, Fig. 2, Fig. 3, the results of the data analyses are shown in box-plots, in which 50% of the data are summarized in the box, the line represents the median and the lines outside of the box represent the 90% confidence interval.

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Fig. 1. Combined lung weight and amount of pleural effusion in relation to postmortem interval: (a) saltwater drowning, (b) freshwater drowning.

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Fig. 2. Combined lung weight and total value of the lung weight and amount of pleural effusion in total cases with regard to the causes of death (postmortem interval <3 days).

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Fig. 3. Total value of combined lung weight and amount of pleural effusion in non-elderly (<60 years of age) and elderly (>60 years of age) males (a) and females (b) with regard to the causes of death (postmortem interval <3 days).

3. Results 

4. Discussion 

In the diagnosis of drowning, overinflated heavy lungs with a substantial amount of pleural effusion are often important pathological findings [10], [11]. An increase in the lung weight is usually due to pulmonary congestion and edema from various etiologies including circulatory disturbance, hypervolemia, hypoproteinemia and pulmonary microvascular injury (e.g. infection, toxic gas inhalation, liquid aspiration, drugs and chemicals, and traumas), which may consequently be associated with pleural effusion [1], [10], [34]. At the time of autopsy, pleural effusion may be increased by postmortem transudation dependent on the water contents of the lungs and postmortem interval [11], [31], [35].

In the present study of drowning cases, a gradual postmortem decrease in the lung weight and a reciprocal increase in the pleural effusion suggested a contribution of postmortem transudation from the lungs to the amount of pleural effusion [11], [31], although this may be valid only for acute death cases without preexisting effusion. A delayed postmortem decrease in the total value of the combined lung weight and the amount of pleural effusion, which was marked in saltwater immersion, may possibly be due to a leakage of the effusion out of the thoracic cavity under an osmotic effect of the immersion medium [11]. This late postmortem phenomenon may more greatly reduce the total lung weight in saltwater immersion, suggesting a factor related to controversial findings on the lung weight difference between freshwater and saltwater drownings [10]. Comparing possible combined lung weight at the time of death in early postmortem cases (<3 days postmortem), estimated by adding the combined lung weight and amount of pleural effusion, there was a significant difference among the examined causes of death. This supported a previous explanation for an increase in the lung weight under a contribution of pulmonary congestion from circulatory disturbance in acute cardiac death and that of hypervolemia depending on the amount of the aspirated immersion medium in drowning [1], which may be enhanced by secondary circulatory failure in the agonal period. Further investigation including blood biochemistry is necessary to establish the contribution of the aspirated immersion medium to the increased lung weight.

However, the lung weight depended significantly on the gender and age of the subjects, showing substantial overlapping between the causes of death. In general, the difference between the above-mentioned causes of death was relatively smaller in females than males, and an influence of age was observed in drownings and acute cardiac death. Such an influence of the gender and age of subjects may be another factor for inconsistency in the lung weight difference due to the immersion medium [10]. A characteristic in non-elderly males was a marked increase in lung weight in acute cardiac death approximating the value in freshwater drownings, suggesting a greater contribution of circulatory disturbance possibly depending on the prolonged agonal period in this group.

The above-mentioned findings suggested a partial difference in the pulmonary pathophysiology in drownings, acute cardiac death and asphyxiation significantly dependent on gender and age. The contributory factors to be considered for the differences in the lung weight may be the lung volume mainly related to the physical constitution of the victims (gender), vital pulmonary capacity and cardiac output in combination with the prolonged agonal period related to vital activity (gender and age). In acute death, postmortem lung weight may primarily depend on the individual lung volume and the persistent circulatory disturbance (congestion and edema) during the agonal period. In drowning cases, water aspiration mainly depending on the vital pulmonary capacity may be another contributory factor. Among these factors, the terminal circulation and water aspiration may be related to the survival time or vital activity. In this connection, a difference in the lung weight between freshwater and saltwater drownings, which was observed in non-elderly males and elderly females, may suggest that freshwater may be a greater risk factor in drowning than saltwater in these groups, contributing to shortening the survival time [1], [10], [34]. Since this difference between freshwater and saltwater drownings was insignificant in the other age groups, a simple osmotic effect of the immersion medium on an increase in the lung weight was not interpretable in the present study. However, for the amount of postmortem pleural effusion in drowning, the main contributory factors may be intensity of pulmonary edema at the time of death and an osmotic effect of the immersion medium [11], [31], [35].

In conclusion, there was a gross difference in the total value of the combined lung weight and the amount of pleural effusion (estimate possible combined lung weight at the time of death) among the causes of death: the value was the largest in drownings, followed by acute cardiac death and asphyxiation. However, the value significantly depended on the gender and age of the subjects, suggesting a relation to the individual physical constitution and survival time or vital activity, and a substantial decrease was observed in saltwater immersion after 3 days postmortem. These factors should be taken into consideration in evaluation of the lung weight in the diagnosis of drownings.