Review Question - QID 108886

A 25-year-old G1P0000 female presents to the obstetric triage center with painful uterine contractions for the last 2 hours. She states that they have become increasingly intense and closely spaced. They now occur every 1-2 minutes. She also endorses a gush of clear fluid about 1 hour ago but denies any vaginal bleeding. The fetal movement has been strong the entire time. The patient has a past medical history of mild intermittent asthma for which she uses an albuterol inhaler. Her prenatal course has been uncomplicated aside from her Rh-negative status, for which she received Rhogam at 28 weeks. In the triage center, the patient’s temperature is 98.4°F (36.8°C), blood pressure is 134/72 mmHg, pulse is 75/min, and respirations are 14/min. She appears comfortable between contractions, has minimal peripheral edema, and has unremarkable cardiovascular and pulmonary exams. Fetal position is confirmed to be cephalic, and external fetal monitoring is shown in Figure A. The patient’s cervix is 5 centimeters dilated and 75% effaced, and the fetus is at -2 station. The patient is admitted to labor and delivery, and an epidural is placed. Ten minutes later, the fetal heart rate tracing is as shown in Figure B. Which of the following is the underlying physiology of this patient’s current fetal heart rate tracing?