ABSTRACT
Previous studies of the baroreceptor response to a 45° head-up tilt in preterm and
mature infants during the first 3 days of life failed to demonstrate a significant
tachycardia while eliciting a 25% reduction in limb blood flow. In order to determine
if maturity or respiratory distress affected the presence of tachycardia after tilting,
34 infants between 28 and 40 weeks gestation, including 15 infants with RDS, were
studied serially during their hospitalization in a neonatal intensive care unit. In
the first 5 seconds after a rapid (1-second) tilt to 45°, individual infants responded
with changes in heart rate (HR) ranging from a fall of 8 beats/min to an increase
of 13 beats/min. Individual responses were not predictable on the basis of maturity
at birth, age after birth, or presence of clinical respiratory distress. The group
as a whole demonstrated a statistically significant increase of 2 ± 4 beats/min in
the first 5 seconds immediately after tilting. This may be compared to a coefficient
of variation of ± 4-5% in the resting HR of the same group of infants. Because of
the unpredictability of individual responses and the small magnitude of the response
for the group as a whole, it can be concluded that the HR component of the baroreceptor
response is poorly developed during the neonatal period.
