AJP - Regulatory, Integrative and Comparative Physiology, Vol 262, Issue 3 452-R458, Copyright © 1992 by American Physiological Society
Developmental changes in continuity and stability of breathing in the fetal lamb
H. H. Szeto, P. Y. Cheng, J. A. Decena, D. L. Wu, Y. Cheng and G. Dwyer
Department of Pharmacology, Cornell University Medical College, New York, New York 10021.
Developmental changes in the continuity and stability of fetal breathing
patterns were studied in 27 fetal lambs with chronically implanted
electromyographic electrodes in the diaphragm throughout the third
trimester (102-140 days). The results showed that there was a progressive
decrease in the incidence of fetal breathing movements throughout the third
trimester (P less than 0.001). This reduction in incidence of fetal
breathing movements was due, in part, to a 20% decrease in the total number
of breathing bursts at approximately 125 days (P = 0.05). The breathing
patterns in both immature (less than 120 days) and mature fetal lambs were
fragmented by a large number of pauses (interburst interval 6-10 s) and
apneas (interburst interval greater than 10 s). Increase in gestational age
was associated with a decrease in the number of pauses and apneas but
longer apnea durations. The breathing pattern in fetuses less than 120 days
old was more continuous than that in those greater than 120 days old, as
demonstrated by significantly longer epoch durations (P = 0.013). There was
no significant change in the continuity of the breathing pattern after 120
days. However, there was a significant increase in the stability of the
instantaneous breathing rates throughout the third trimester. This was
indicated by a significant increase in the percent of breathing bursts that
occurred in stable clusters (P = 0.046), the number of bursts per cluster
(P = 0.013), and cluster duration (P = 0.018). Thus an increase in
stability appears to be the major developmental change in breathing control
in late gestation.
