Susan Coons

DEVELOPMENT OF CONSOLIDATED SLEEP AND WAKEFUL PERIODS IN RELATION TO THE DAV/NIGHT CYCLE IN INFANCY

Periods of sustained sleep were analyzed to assess the development of sleep‐state organization and structure during the first six months of life. Infants first establish consolidated sleep and wakeful periods, which then become oriented to the 24‐hour day/night cycle. As infants mature they gradually show greater sleep ‘efficiency’, and at onset of sleep, REM periods become less likely. The longest sleep period progressively becomes associated with the dark period of the 24‐hour cycle. This study also assessed the sequences of NREM‐REM sleep‐cycle organization during the first six months of life. Although individual infants may have a significant correlation between duration of sleep and latency at onset of sleep, the over‐all direction is not constant, nor is an ‘age effect’ apparent during the first six months. The data support the hypothesis that states of alterness, which develop independently in the perinatal period, become integrated in early infancy.

Apnea and bradycardia during feeding in infantsweighing >2000 gm*

One full-term and nine premature infants who had been or were about to be discharged from thehospital were studied to identify any breathing problems. While awake and when sucking and swallowing, the infants had central apnea accompanied by significant bradycardia and significant drops in transcutaneous oxygen values. These events occurred whether infants were breast-fed or ingested human milk, formula, or water by bottle, and were not associated with falls in esophageal pH. While awake, after occlusion of both nostrils, the infants responded with mouth breathing. Sleep-related apneic episodes were also found but were less significant. The long apneic events were related to poorly coordinated sucking and breathing while awake.

Development of sleep-wake patterns and non-rapid eye movement sleep stages during the first six months of life in normal infants

Thirty-one normal infants were selected for 24-hour polygraphic monitoring at different ages during the first six months of life. The development of sleep-wake distribution patterns during day and night was observed. Qualitative changes in non-rapid eye movement (NREM) sleep as it becomes differentiated in stages 1, 2, and 3-4 were measured. Sustained periods of wake are present by 6 weeks of age. After 3 months of age, wake is predictably distributed in late afternoon and early evening. REM sleep is disproportionately distributed within sleep in 24 hours, presenting a higher percent of total sleep during the night. At 4.5 and 6 months of age, stages 2 and 3-4 NREM are coincident during the nocturnal hours and 3-4 NREM sleep peaks in the early period of the night. The decreasing proportion of REM sleep, particularly in its daytime distribution, suggests a reciprocal relationship to the developing of wakefulness.

GENE VARIATION IN HUMAN PULMONARY SURFACTANT PROTEIN SP-B: Deletion in an intron between exons 10-11 in an RDS infant. 334

Genomic DNA from Respiratory Distress Syndrome (RDS) and non RDS subjects was used to amplify the gene for pulmonary surfactant protein SP-B by the polymerase chain reaction (PCR). The 10 kilobase (kb) SP-B was amplified in 5 segments which were then cloned and sequenced. The sequence of each segment for samples from both groups was compared to the published genomic sequence for SP-B (HUMSPBAA) in the genebank. A number of sequence differences were observed: in the 5′ untranslated region, in exons 3 and 5, and exon 11, the 3′ untranslated portion of mRNA. A number of DNA sequence differences were also observed in introns. A short form of segment 5 (exon 10- exon 11) was amplified from genomic DNA of an RDS sample. The DNA sequence is similar to SP-B but has a 400 basepair (bp) deletion in the intron, and some changes in exon 11. Since the normal allele for segment 5 of human SP-B was also amplified from this sample, the RDS subject is probably a heterozygote, or this fragment is a duplication and rearrangement of the 3′ portion of the SP-B gene. Exon 11 makes up the 3′ untranslated region of the mRNA, and any changes in this region could affect mRNA stability.