Phrenic nerves and diaphragms in sudden infant death syndrome

Metabolic acidosis and sudden infant death syndrome: overlooked data provides insight into SIDS pathogenesis

BACKGROUND

Decades of mainstream SIDS research based on the Triple Risk Model and neuropathological findings have failed to provide convincing evidence for a primary CNS-based mechanism behind putative secondary dyshomeostasis (respiratory or cardiac) or impaired arousal. Newly revealed data indicate that severe metabolic acidosis (and severe hyperkalemia) is a common accompaniment in SIDS. This supports the direct effect of sepsis on vital-organ function and occurrence of secondary CNS changes accompanied by the dyshomeostasis leading to SIDS.

DATA SOURCES

Using PubMed and Google Scholar literature searches, this paper examines how metabolic acidosis and sepsis might contribute to the underlying pathophysiologic mechanisms in SIDS.

RESULTS

The discovery of a series of non-peer-reviewed publications provided the basis for a serious examination of the role of metabolic acidosis and sepsis in SIDS. Most SIDS risk factors relate directly or indirectly to infection. This consequently elevated the position of septic or superantigenic shock and viremia in causing secondary organ failure leading to SIDS. The latter could include diaphragmatic failure, as evidenced by peripheral respiratory (muscle) arrests in experimental septic shock, as well as infectious myositis and diaphragm myopathy in sudden unexpected deaths, including SIDS. In addition, just as acidosis lowers the threshold for ventricular fibrillation and sudden cardiac arrest, it could also contribute to similarly unstable diaphragm excitation states leading to respiratory failure.

CONCLUSIONS

This paper uniquely reveals compelling evidence for a connection between metabolic acidosis, sepsis, viral infections, and sudden unexpected child deaths and provides a solid basis for further work to define which pathway (or pathways) lead to the tragedy of SIDS. It is recommended that all autopsies in sudden unexpected deaths should include pH, bicarbonate, lactate, and electrolyte measurements, as well as diaphragm histology.

Intact numbers of cerebellar purkinje and granule cells in sudden infant death syndrome: a stereologic analysis and critical review of neuropathologic evidence

Despite much research during recent decades, the etiology and pathogenesis of sudden infant death syndrome (SIDS) remain unknown. Because of the role of the cerebellum in respiratory and cardiovascular control, it has been proposed that it plays an important role in the pathogenesis of SIDS. To date, 5 postmortem studies on the cerebellum of SIDS cases have yielded conflicting results. Using a rigorous design-based stereologic approach, we investigated postmortem cerebella from 9 SIDS patients who died between 2 and 10 months of age and from 9 age- and sex-matched control children. Neither the volumes of the cerebellar external granule cell layer, molecular layer, internal granule cell layer (including the Purkinje cell layer), and white matter nor the total numbers of Purkinje cells, granule cells in the internal granule cell layer, and the number of granule cells per Purkinje cell showed statistically significant differences between the SIDS cases and the controls. Based on these observations, we conclude that structural alterations in cerebellar development are not involved in the etiology and pathogenesis of SIDS.

Sudden death of an infant with bronchopulmonary dysplasia and bilateral cervical lymphadenopathy--a vagal death?

A sudden unexpected death is reported in a 15-month old boy, born with an extremely low birth weight and then had suffered prolonged respiratory complications arising from infantile respiratory distress syndrome. The autopsy revealed severe bronchopulmonary dysplasia (BPD) in his lungs with secondary pulmonary heart disease; a tracheotomy was carried out to enable his survival. The cause of death was established as being acute cardiac and pulmonary failure due to severe BPD, rather than mechanical asphyxia. The perilaryngeal lymph nodes were also significantly enlarged and closely surrounded the vagus bilaterally. Such cervical lymphadenopathy could have resulted in the mechanical compression of the vagus upon movement of the neck. For this reason, anatomical examination of the cervical portion of the vagus and its path may be of great significance when analyzing the cause of death in the cases of sudden infant death.