Previous studies have identified numerous environmental risk factors for sudden infant death syndrome (SIDS), e.g., prone or side sleeping positions, overheating, and maternal smoking, and post-mortem studies indicate that SIDS babies may have neurotransmitter receptor defects. To better understand how these factors affect the respiratory neural network output, their effect on the respiratory center have been examined by the means of using the approximate entropy Method.

To accomplish this, the study is completed in 3 separate parts. The first part is a heating study where rat subjects are heated from control (36-37 C) to mild heating (38-39 C) to the final severe heating level of 40C. The second part of the study involves the use of nicotine to mimic second hand smoke by the mother, the other significant risk factor. In this portion of the study the animal subjects are heated as before in the heating study but they receive a daily dose of nicotine (2.5 mg/kg) in the form of an Intraperitoneal (ip) injection. This group is complemented by the use of a group that only received saline in the injections as a form of control.

In the final set of experiments, the same experimental protocol as in the previous study was adopted with the addition of muscimol to the protocol. Muscimol was given to the neurons in the brainstem to inhibit their activity. Results from these experiments show that the complexity of the respiratory neural network output decreases with the level of heating. Data also shows that nicotine causes even a further decrease in complexity values when compared to heating alone. The effects of muscimol are profound on the respiratory neural networks as evidenced in the data. The overall complexity of the system was even lower when compared with nicotine and heating alone or combined. This suggests that these three factors can be a deadly combination for a SIDS infant.