What is the Meaning of Fetal Heart Rate Patterns according to Physiopathology?

Abstract

The analysis and interpretation of the Fetal Heart Rate in the parturition watch have shown their limits in the identification of the fetuses risking neonatal asphyxia, which consequences are death or Cerebral Palsy. The weak specificity of the continuous electronic heart rate monitoring generates an unjustified C-section excess, associated to an increasing of the immediate and ulterior materno-fetal morbi-mortality. Presently, the visual analysis of the Fetal Heart Rate exclusively lays on chronomorphological patterns. However, there is another way that calls on the knowledge of the physiological processes of the fetus’ cardiovascular control: In situation of normoxemia, the peripheral baroreceptors of the near term fetus is responsible for the control of the arterial pressure with both systems in action: the permanent accelerating sympathetic system and the intermittent braking parasympathetic system, which causes short-term variability. In situation of acute hypoxemia, the peripheral chemoreceptors are stimulated and induce a rapid vagal mediated fall in heart rate (i.e. deceleration), and a peripheral vasoconstriction mediated by sympathetic nervous system. In situation of acidosis, the central chemoreceptor is activated. It then stimulates the sympathetic system generating a fetal tachycardia, and inhibits the functioning of the peripheral baroreceptors, producing minimal to absent variability. From that comes out that the variability and the heart baseline are the only two patterns that reflect the fetal prognosis.