ABSTRACT
It has been just over 20 years since the publication of a classic report by Dawes et al. (Dawes, Fox, Leduc, Liggins, & Richard, 1972) in which they provided the initial detailed description of the rapid irregular breathing movements of the chronically instrumented fetal lamb. With the advent of technology for high-resolution ultrasound shortly thereafter, it became possible to document the occurrence of breathing activity and other aspects of fetal behavior in the human fetus during the course of gestation (Pillai & James, 1990b). From studies in these and other species it became clear that under normal conditions fetal breathing movements are intermittent. Epochs of fetal breathing activity of variable duration are interspersed over time with periods of apnea that are equally variable in duration. Research suggests that mechanisms that act to generate this periodicity do so by inhibition of fetal breathing movements (Bryan, Bowes, & Maloney, 1986; Jensen & Chernick, 1991). These regulatory processes may be in part a specialized adaptation to the demands of fetal life and serve to promote conservation of oxygen and nutrient supply. On the other hand, the presence of these movements, at least for some part of the time, is essential for growth of the lungs and development of normal pulmonary architecture (Alcorn, Adamson, Maloney, & Robinson, 1986).
