1642 THE EFFECT OF A THERMAL STRESS ON RESPIRATION IN PREMATURE INFANTS DURING SLEEP

Abstract

Cool temperatures have been associated with a reduction in the frequency of apnea. In premature infants, most respiratory pauses (RP) occur during periodic breathing (PB). A decreased frequency of RP during cooling may therefore be related to 1) a decrease of RP during PB, non-PB, or both and/or 2) a decrease in the relative amount of PB. To sort out these relationships, we evaluated the frequency of RP and the amount of PB in 5 premature infants subjected to a mild thermal stress during sleep. The infants were studied under radiant warmers for 6-8 hours while measurements of respiration and body temperature were made. Cooling was accomplished by allowing skin temperature to fall slowly for short periods 4-10 times during the study periods. Breathing pattern (PB or non-PB) and state were assessed, and an index (RI) reflecting the % of time apneic, was calculated for each 60 sec epoch. PB occurred in all subjects and accounted for 11-60% of the total sleep time. Most pauses occurred during PB compared to non-PB (mean RI=30±7% and 6±2%, respectively). During cooling the mean RI decreased (18.6±5.7% and 12±5.5% for warm and cool periods, respectively), but there was no change in the mean RI during cooling for episodes of either PB or non-PB when evaluated separately. However, the relative amount of PB decreased during cooling (43±15% to 22±14%, p<.05). We conclude that the decrease in the mean RI during cooling was due to a decrease in the relative amount of periodic breathing.