The role of pulmonary surfactant in SIDS

Sudden infant death syndrome (SIDS): Microgravity and inadequate sensory stimulation

In early gestation, the human foetus develops in a buoyant environment, which is similar to the near-weightlessness of space flight. After the 26th week of gestation, the foetus gradually becomes exposed to gravitational forces. The influence of fluid immersion declines as the weight of the foetus increases. In this way, the foetus adapts and trains for the gravity environment after birth. Failure of gravitational loading in the last trimester of pregnancy delays development and maintains the pathophysiological environment of microgravity as experienced by the astronaut in space flight. The deconditioning effects of microgravity during space flight are the reverse processes of intrauterine development after the 26th week when the foetus begins training body processes for adaptation to an earthly environment. Growth requires space and movement, which suggests that a growth-retarded foetus may have been deprived of the mechanical dimension of uterine wall pressure, and, in twins, the smaller sibling may have been deprived of space. The behaviour of a study group of sudden infant death syndrome infants suggested a continuation of the effects of the foetal akinesia syndrome during the third trimester period of gestation. NASA research into the pathophysiology of microgravity was based on a simple insight: that the physiological effects of human space travel were virtually identical to the adjustments the body makes when lying down. This is the same environment as that of the human foetus in the first 22 weeks of gestation after which the uterine environment becomes a prelude to adaptations to the force of gravity.

Can superantigens trigger sudden infant death?

A majority of sudden infant death syndrome (SIDS) victims have respiratory or gastrointestinal infections prior to death. This has led to an investigation of the role of pathogenic bacteria and the potentially lethal toxins they produce as triggers for sudden infant death. A small group of bacteria have been consistently identified in SIDS victims as compared to controls, and remarkably, three of these produce superantigenic toxins. Superantigens exert a powerful effect on the immune system, stimulating T-cells, which subsequently induces the formation of large amounts of cytokines. Generation of an overwhelming inflammatory response may lead to death by shock, or other, as yet unrecognized effects of the toxin on the respiratory or cardiac systems. A SIDS/superantigen model is proposed which may explain many of the pathological characteristics of SIDS and establish quantifiable markers for SIDS.

A comparison of lung lamellar body phospholipids from premature and term infants: is sphingomyelin a contaminant of surfactant?

Lamellar bodies were isolated from homogenates of lungs obtained at autopsy from premature infants (n = 9), and compared to lamellar bodies from three full term reference groups including 55 infants with sudden infant death syndrome (SIDS), 14 control infants, and 3 who succumbed to intra-uterine death (IUD) at term. Analysis of the phospholipids was expected to reveal a high proportion of sphingomyelin (Spm) in the lamellar bodies isolated from the lungs of premature infants (24 to 33 weeks gestational age) since at this stage of their development the percentage of Spm in the amniotic fluid is high. However, Spm was either absent or a small proportion of the total phospholipid in lamellar body surfactant from these premature infants. Spm was also a small percentage of phospholipid in the lamellar body surfactant of infants with SIDS and from control and IUD specimens. It is suggested that Spm may not be a normal constituent of lamellar body surfactant but rather a contaminant from membranes.