Fetal breathing movements are associated with changes in compliance of the left ventricle.

We have tested the hypothesis that the limited fetal ventricular distensibility is not only an intrinsic cardiac characteristic but is also contributed to by the pressure exerted by the intrathoracic organs. To this purpose we have studied the diastolic cardiac function by Doppler velocimetry in 11 fetuses during fetal breathing and in 22 fetuses during apnea, controlling for gestational age at examination and heart rate. Inspiration was associated a significant increase in left ventricular compliance, as measured by deceleration time (inspiration 182.6 +/- 15.5 s vs. expiration 137.1 +/- 13.1 s vs. apnea 151.7 +/- 51.8 s), and in ventricular filling, as measured by velocity time integral (inspiration 0.086 +/- 0.020 m vs. expiration 0.064 +/- 0.014 m vs. apnea 0.065 +/- 0.011 m), compared with both the expiration and apnea groups. These increases most likely reflect changes in venous return and ventricular end-diastolic volume secondary to a decrease in intrathoracic pressure during fetal breathing.

Alterations in ventricular filling in small-for-gestational-age fetuses.

OBJECTIVE: This study was designed to evaluate if fetal diastolic cardiac function is compromised in small-for-gestational-age (SGA) fetuses with documented fetal well-being at the biophysical profile. STUDY DESIGN: We have compared indices of diastolic cardiac flow in singleton SGA fetuses with forward diastolic flow in the umbilical artery at Doppler velocimetry and documented fetal well-being (n = 10) with those of appropriate-for-gestational-age (AGA) controls with documented fetal well-being matched for gestational age at ultrasound (n = 20). RESULTS: At the mitral valve, velocity time integral (VTI) (0.059+/-0.011 vs. 0.069+/-0.011 m, p = 0.04), peak velocity of the A wave (0.426+/-0.043 vs. 0.498+/-0.087 m/s, p = 0.005), and acceleration time of the E wave (0.046+/-0.004 vs. 0.053+/-0.007 s, p = 0.008) were significantly different between SGA and AGA fetuses. At the right atrioventricular valve, only VTI was significantly different between SGA and AGA fetuses (0.065+/-0.014 vs. 0.078+/-0.011, p = 0.03). CONCLUSIONS: These findings suggest that SGA fetuses have significantly lower left and right ventricular diastolic filling compared with AGA fetuses without significant changes in diastolic function.