Analysis of the heart rate and breathing patterns of infants destined to suffer sudden infant death syndrome: probability density function analysis.

From a prospective study into the sudden infant death syndrome in which 24-h recordings of the ECG and respiratory waveform (abdominal wall movement) were made on a population of full-term infants, 22 recordings were obtained on 16 infants who subsequently suffered sudden infant death syndrome. The probability density function for the instantaneous heart rate and the breath to breath intervals and their randomly variabilities were calculated for these 22 recordings and for a control group of 324 infants randomly selected from the remainder of the population. A principal components analysis was then performed to classify the data and to make comparisons between infants. The infants in the analysis were divided into three postnatal age groups. No differences were found between the sudden infant death syndrome cases and the control group for the breath to breath intervals and its variability or for the instantaneous heart rate. Three sudden infant death syndrome cases lay outside the range of values for the heart rate variability at 6 wk of age.