8 - Fetal Breathing

Abstract

This chapter discusses the breathing process in fetus. Recordings of intrathoracic pressure in fetal sheep in utero show both isolated and rhythmical respiratory movements. Rhythmical movements are typically shallow and rapid, although the frequency is highly variable. During the last month of gestation, these rapid and irregular breathing movements occur in episodes during which rapid eye movements are present and the electrocorticogram is devoid of large-amplitude slow waves. The volume of fluid that moves along the trachea during the inspiratory efforts is usually less than 1 ml. Fetal breathing movements are accompanied by electrical activity in the muscle of the diaphragm and in the phrenic nerve. In confirmation of the belief that fetal breathing is a result of central neural activity, unitary discharges have been recorded in the medulla of fetal sheep in phase with phrenic nerve activity and deflections in tracheal pressure. The most widely used method of the detection of fetal respiratory activity in chronic animal studies involves the measurement of pressure changes within the respiratory tract. Electromyography, which is the detection of electrical activity of contracting muscles, has been used to analyze the involvement of individual muscle groups in fetal breathing.