Abstract 1168 Poster Session I, Saturday, 5/1 (poster 3)

The mechanism by which prone sleeping position increases the risk for SIDS is not yet known. In Our earlier study in preterm infants at 36 w PCA(Goto et al., Pediatrics, In Press), we have shown that the first quiet sleep (QS) after feeding was significantly longer, the number of awakenings were lower and overall heart rate variability was less in prone vs. supine positions. In the present study we have examined the level of autonomic control of heart rate by measuring standard deviation of heart rate (SDHR) as well as low frequency ( LF; 0.02-0.19 Hz) and high frequency ( HF; 0.2-1.5 Hz) heart rate variability. Twelve low risk preterm infants (31-35 w GA) were recorded at 36 w postconceptional age (PCA) and 8 other infants at 1 m corrected age (CA) with time-lapsed videosomnography (TLVS) and continuous ECG both in prone and in supine positions. Heart rate variability analysis was carried out using artifact free digitized ECG records during the first AS and QS episodes after feeding. Table below summarizes the SDHR findings.

Table 1 No caption
Full size table

SDHR was significantly higher during quiet sleep in supine position. LF and HF were higher in supine vs. prone position in both sleep states. Based on this and our earlier study we conclude that the longer QS episodes after feeding, fewer awakening during sleep together with lower heart rate variability constitute higher arousal threshold and thereby increasing the vulnerability of the infants for SIDS in prone position.