Investigation of Suffocation Mechanisms in the Infant Sleep Environment Using a Mechanical Breathing Model Simulation

Mattress firmness has long been recognized as a protective factor for sudden unexpected infant death (SUID) with mandatory infant mattress firmness regulations enforced by the US Consumer Product Safety Commission (CPSC) since August 2022. Recent research has revealed that two mechanisms are involved in SUID due to suffocation: airflow resistance (AR) and carbon dioxide rebreathing (CO₂RB). By gaining an in-depth understanding of these mechanisms, existing bedding products can be evaluated and new products designed with infant safety as the primary consideration. This paper describes experiments and their results using a mechanical breathing model to elucidate the relationship and differences between these two mechanisms of suffocation. The model was configured to measure the work of breathing (WOB) and carbon dioxide (CO₂) rebreathing in the setting of increasing airflow resistance and increasing CO₂ storage capacity, simulating but separating both potential respiratory hazards in infant sleep environments. The first series of experiments simulate increasing airflow resistance by using orifices of decreasing diameter. The second series simulates increasing the CO₂ storage capacity of the bedding material by using an open-ended tube surrounded by an increasing thickness of soft (low-resistance), porous polyfill material. The third series of experiments were conducted to investigate both hazard mechanisms in combination. The results show that increasing airflow resistance and CO₂ rebreathing are independent suffocation hazards, each with its own adverse effects that may occur independently or in concert, with cumulative effects.