Incomplete Baroreceptor Responses in Newborn Infants

Abstract

Previous studies of the baroreceptor response to a 45 degree 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 degrees, 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.

Development of baroreflex control of heart rate in preterm and full term infants

“…In the few other studies available on the ontogeny of BRS in the human newborn, the baroreflex was evaluated by the magnitude of the heart rate response to body tilting. With this method, results were controversial: some 14 reported a poorly developed response in the newborn, independent of the length of gestation, age after birth, and respiratory status, whereas others 15-17 observed a well developed response in healthy premature and full term infants. Results from animal studies are even more conflicting.…”

Changes in baroreceptor vagal reflex performance in the developing rat

“…In larger mammals, including human infants [12], lambs [7], piglets [10,11,23], puppies [29], and kittens [13], baroreceptor reflex sensitivity increases steadily throughout postnatal life. In the rat, in contrast, baroreceptor reflex function at P5/6 was comparable to that in the adult but underwent a postnatal period of attenuation between P10 and P20.…”

Effects of spaceflight on postnatal development of arterial baroreceptor reflex in rats

“…In many mammalian species, the arterial baroreceptor reflex changes functionally during development and the functional changes of the reflex are known to be important to maturational changes in haemodynamics (Hutchinson et al 1962, Struyker-Boudier et al 1982, Holden et al 1986, Shimizu et al 1990, Patton & Hanna 1994, Kasparov & Paton 1997. In the case of rats, a dramatic increase in baroreceptor reflex performance is observed between days 20 and 25 after birth (Kasparov & Paton 1997).…”