The numbers have remained fairly constant. Autopsies are recommended after all SIDS deaths, but typically they reveal the same sparse information as Dominic Miller's. The baby had pinhead hemorrhages in his lungs, but nothing else. The tiny bleeding spots, called petechiae, are found in many SIDS babies and in other ailments as well. With SIDS babies, Krous suspects the hemorrhaging is caused by vigorous but futile efforts to resume breathing after a period of sleep apnea, when breathing stops for a few seconds.
Most babies rouse themselves easily from such episodes, which are normal.
But the leading SIDS theory suggests that affected babies have subtle brain-stem abnormalities that block normal arousal or alarm reflexes. Dr. Hannah Kinney, a neuropathologist at Harvard and at Children's Hospital in Boston, developed his theory during several years of research on animals and infants. Kinney says certain babies are born with chemical defects in the lower portion of the brain stem called the ventral medulla, which is involved in alarm reflexes. It regulates blood pressure and breathing during sleep, and controls how the baby responds to low oxygen blood levels and high amounts of carbon dioxide. Lack of oxygen and excessive carbon dioxide can occur when a baby is sleeping on his or her stomach, or face down.