Cardiovascular changes associated with fetal breathing.

Studies were carried out on seven fetal lambs, 3 to 1 weeks prior to the expected date of delivery to determine if, during fetal breathing, cardiovascular events were similar to those described as occurring with respiration after birth. The following changes were observed; (1) a slight decrease in pressures with the initiation of the rapid inspiratory movements followed by: (2) a marked elevation of the systolic and diastolic pressures; (3) a cyclic variation characterized by a fall in arterial pressure with inspiration; (4) a variable acceleration of the heart rate; and finally, (5) a typical respiratory arrhythmia. These findings demonstrated that, during fetal respiratory movements, there are some cardiovascular changes which are specific to this period of life. There are other changes which are identical to what has been observed after birth. These latter cardiovascular changes imply that the endotracheal pressure variations are the reflection of authentic inspiratory movements under the influence of the central nervous system.