Our purpose was to identify and further characterize physiologic mechanisms relevant to autoresuscitation from hypoxic apnea in infants dying suddenly and unexpectedly. We studied cardiorespiratory recordings of 24 infants (age range, 0.8-21 months) who died suddenly while being monitored at home. These recordings were analyzed for features indicated by studies in animal models to be characteristic of hypoxic gasping, and of recovery from bradycardia and apnea associated with gasping (e.g., autoresuscitation). Findings in 5 infants diagnosed as having sudden infant death syndrome were compared with 6 non-SIDS infants whose deaths resulted from other conditions. Additionally, we studied 15 healthy infants during sleep, using home monitor and other respiratory recording techniques, in order to obtain comparison data. We found in recordings from 23 of 24 subjects that hypoxic gasps with characteristic features occurred immediately preceding death. A unique pattern of complex, closely spaced gasps ("double" or "triple" gasps) was present in many subjects. Evidence of partially successful autoresuscitation closely following one or more gasps occurred in 11 subjects, while another 4 had evidence of complete autoresuscitation with return of normal heart rate and resolution of apnea on one or more occasions. Significant differences between SIDS infants and those dying from other causes included increased occurrence of complex gasps and decreased occurrence of partial or complete autoresuscitation in the SIDS infants. The non-SIDS cases were different from the SIDS cases in that only one had "double" gasps (n = 7), while none had "triple" gasps, as compared with 4 out of 5 SIDS cases with these patterns (P < 0.05, chi-square). Also, in contrast with the SIDS cases, more of the cases with specific postmortem diagnoses had evidence of partial (5 out of 6 cases) or complete (1 out of 6 cases) autoresuscitation (P < 0.05, chi-square). We conclude that partial or complete autoresuscitation by gasping is not uncommon in moribund infants during the first year of life. Failure of autoresuscitation mechanisms other than failure to initiate gasping may be characteristic of infants dying of SIDS. Some SIDS infants appear to be different from infants dying with other diagnoses with respect to efficacy and characteristics of hypoxic gasping.

To test whether alveolar hypoventilation and an abnormal ventilatory response to inhaled carbon dioxide explains some episodes of sudden-infant-death syndrome, we assessed ventilatory control during quiet sleep in 12 normal infants and 11 infants who had required at least two resuscitations because of prolonged apnea (greater than 20 seconds) during sleep (aborted form of the syndrome). Infants with the aborted syndrome hypoventilated during quiet sleep (alveolar partial pressure of carbon dioxide, 38.9+/-3.5 mm Hg) as compared to normal infants (35.1+/-1.9, P less than 0.01). In addition, the ventilatory response to carbon dioxide breathing during quiet sleep was impaired (mean change in minute ventilation per change in partial pressure of carbon dioxide 22.1+/-8.9, as compared to 63.1+/-19.1 ml per kilogram per minute per millimeter of mercury in controls [p less than 0.001]). Three infants with the "aborted syndrome" subsequently died during sleep at home; autopsy, done in two, revealed no apparent cause of death. We conclude that infants who have had an episode consistent with sudden-infant-death syndrome have a defect in the regulation of alveolar ventilation.

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The pediatric pneumogram is a frequently used tool in the diagnosis and management of apnea during infancy. We analyzed 287 pneumographic recordings from 123 full-term infants (63 males) obtained during the first 12 months of life to establish normative values for apnea, periodic breathing, and bradycardia. The results of the analysis were compared by sex and age. The number of infants who exhibited periodic breathing decreased significantly over time (78% at 0-2 weeks vs 29% at 39-52 weeks; P less than 0.05). However, for those infants who did breathe periodically, the percent of sleep time spent in this breathing pattern did not change with age. No apnea greater than or equal to 15 seconds was recorded in any infant, and apnea density (total apnea greater than or equal to 10 seconds in minutes/100 minutes sleep time) did not change with age or sex. Using our definitions, no bradycardia was identified. Normal full-term infants occasionally have apnea of 10, 11, or 12 seconds, and, until 6 months of age, the majority will have a small amount of periodic breathing (less than 1% of sleep time) during sleep at home.