Body position, sleep states, and cardiorespiratory activity in developing low birth weight infants

The objective of this study was to determine the effects of body position ( supine vs prone) on cardiorespiratory activity during quiet and active slee p in growing low birth weight (LBW) infants. The effect of postconceptional age on cardiorespiratory activity in the two positions was also evaluated. Fifty-one healthy, growing, appropriate for gestational age LBW infants (7 95-1600 g), ranging from 26-37 weeks in gestational age, were evaluated. Al l subjects were enrolled in an ongoing study of the effects of quality of d ietary energy on the rate and composition of weight gain. Infants were rand omly assigned to the supine or prone position for the first: 3 h of the 6-h studies; the position was reversed for the second 3 h, Continuous recordin gs of cardiorespiratory activity were performed along with simultaneous min ute by minute assignment of behavioral sleep state. Measurements of heart r ate (HR), heart period variability (RR-SD), respiratory rate (f), and respi ratory variability (fSD) were made each minute. Low birth weight infants ha d higher HR and f and lower RR-SD and fSD in the prone position compared to the supine position, during both quiet and active sleep. With increasing p ostconceptional age, positional differences in HR increased during quiet sl eep and differences in RR-SD increased during both sleep states. These data demonstrate systematic differences in cardiorespiratory control related to body position during sleep. We speculate that such positional differences are due to variations in autonomic control, and may, in turn, contribute to variations in susceptibility to sudden infant death syndrome. (C) 1999 Els evier Science Ireland Ltd. All rights reserved.