Immunohistochemical investigation of a pulmonary surfactant in fatal mechanical asphyxia

We evaluated the usefulness of pulmonary surfactant protein A (SP-A) as a practical diagnostic marker of fatal mechanical asphyxia in forensic autopsy cases. A total of 27 cases of asphyxia were examined histologically and immunohistochemically and compared with a control group consisting of 16 cases of poisoning (n = 9) and peracute death (n = 7). Both groups showed histological findings of local atelectasis and local emphysema, congestion, intra-alveolar and interstitial edema in most cases and pulmonary hemorrhages in some cases. The mechanical asphyxia group showed a significantly increased intensity of SP-A staining in the intra-alveolar space accompanied by many massive aggregates in approximately 60% of cases, which was not found in the control group. These structures may be interpreted as aggregates of pulmonary surfactant released from the alveolar wall due to enhanced secretion caused by strong forced breathing or over-excitement of the autonomic nervous system by mechanical asphyxia. The results of our investigation suggest the practical usefulness of the immunohistochemical detection of SP-A in distinguishing mechanical asphyxia from other types of hypoxia.