Related Experiment Video
Updated: Jul 17, 2026

Fetal Mouse Cardiovascular Imaging Using a High-frequency Ultrasound (30/45MHZ) System
Published on: May 5, 2018
Response of fetal heart rate to uterine contractions
1The University of Texas Health Science Center at Houston, Houston, TX, USA.
The heart rate variability of fetuses under stress from maternal uterine contractions conveys critical information to clinicians and also provides theoretical clues about heart rate regulatory mechanisms. According to the polyvagal theory, the deceleration of fetal heart rate under stress is caused by the withdrawal of vagal tone. Recovery is mediated by its reestablishment. An implication of this mechanism is that the respiratory sinus arrhythmia (RSA) is elevated after the deceleration and subsequent recovery. Findings from our clinical data on fetuses support this theory. The data also indicate that in the instance of a late deceleration the RSA may not be elevated after recovery.
The heart rate variability of fetuses under stress from maternal uterine contractions conveys critical information to clinicians and also provides theoretical clues about heart rate regulatory mechanisms. According to the polyvagal theory, the deceleration of fetal heart rate under stress is caused by the withdrawal of vagal tone. Recovery is mediated by its reestablishment. An implication of this mechanism is that the respiratory sinus arrhythmia (RSA) is elevated after the deceleration and subsequent recovery. Findings from our clinical data on fetuses support this theory. The data also indicate that in the instance of a late deceleration the RSA may not be elevated after recovery.
Related Concept Videos
Fetal Circulation
Two umbilical arteries transport blood from the fetus to the placenta. At the placenta, the blood absorbs oxygen and nutrients while simultaneously eliminating waste products. This oxygen-enriched and nutrient-rich blood then returns to the fetus through one...
Regulation of Pulse
Regulation of Heart Rates
The SNS increases heart rate through the release of norepinephrine and epinephrine, which act on beta-1 adrenergic receptors in the heart. This action increases the rate of depolarization in the sinoatrial (SA) node, the heart's...
Conduction System of the Heart
The pacemaker cells are located in two primary nodes: the sinoatrial (SA) node and the atrioventricular (AV) node. The SA node pacemaker cells can autonomously depolarize, triggering an action potential that leads to the...
Dysrhythmias III: Characteristics of Dysrhythmias
Development of the Heart
As the embryo undergoes lateral folding, these paired tubes approach each other, merging into a single primitive heart tube by...

