(JOINT TIME FREQUENCY ANALYSIS) NEW METHOD TO ANALYZE THE DEVELOPMENT OF CIRCADIAN RHYTHM IN PREMATURE INFANTS. 279

Studies regarding development of biological rhythmicity are important in the neonate since it depends on: brain maturation, genetic potential and affected by environment. Previously we have shown that extreme premature infants with BPD do not develop circadian rhythm (CR) during first two months of life although they develop ultradian rhythm (UR). There are not enough data available regarding the development of (CR) in premature infants who have prolonged hospitalization. We studied CR in heart rate (HR) and blood pressure(BP) in 18 low birth weight infants (BW: 1286.42±780.1, GA: 27.59±4.3, Apgar score in 1 and 5 min. 3 and 7 (median) respectively. All required respiratory support and were diagnosed with BPD, but had no CNS disease. Methods: A new mathematical approach to biological signals analysis Joint Time Frequency Analysis (National Instruments) was used. Continuous 24 hour tracings of HR & BP were collected using Hewlett Packard careview program. It allows to find the range of frequencies, changes of the frequency as a function of time and the intensity of particular frequencies. HR was measured every 60 sec. BP every 30 min. at the end of 2nd, 4th, 6th, and 8th week of postnatal age(PNA). Overall we had 44 recordings. The data were analyzed to find length of cycle and appearance of UR and CR (table).Results: No biorhythmicity was found until 4 wks PNA. UR began to appear after 4 weks PNA and CR appear after 8 wks PNA. Among the 13 infants, 46 wks PNA 69% (9/13) develop UR (3±0.5 h in length). All 13 were on ventilator. 4 (80%) out of 5 infants ≥8wks PNA developed CR (24±2 h in length). These 4 were off ventilator support. One who did not develop CR was still on ventilator, but he continue to manifest UR.Conclusion: The biorythmicity in HR and BP, in ELBW infant does not appear until after 4 wks PNA. UR proceeds the development of CR. Development of CR is affected be ventilatory dependency.