Power spectral analysis of R-R interval variability before and during the sinusoidal heart rate pattern in fetal lambs.
OBJECTIVE
The appearance of the sinusoidal heart rate pattern found on fetal cardiotocograms has not been fully explained, either physiologically or clinically. In this study we performed power spectral analysis on the sinusoidal heart rate pattern obtained by administration of arginine vasopressin and atropine sulfate to investigate its frequency components in fetal lambs with long-term instrument implantation.


METHODS
Eleven tests were performed in 4 fetal lambs at 120 to 130 days' gestation. An artificial sinusoidal heart rate pattern was obtained by administration of atropine sulfate and arginine vasopressin in 9 tests. An autoregression model was used to compare the spectral patterns before and during the sinusoidal heart rate pattern.


RESULTS
Marked decreases in low-frequency (0.025-0.125 cycles/beat) and high-frequency (0.2-0.5 cycles/beat) areas were observed in the presence of the sinusoidal heart rate pattern. However, there were no significant changes in the very-low-frequency area (0.01-0.025 cycles/beat), which corresponds to the frequency of the sinusoidal heart rate pattern.


CONCLUSIONS
The sinusoidal heart rate pattern may represent a very low-frequency component inherent in fetal heart rate variability that appears when low- and high-frequency components are reduced as a result of strongly suppressed autonomic nervous activity.
Suzuki
T
T
Department of Obstetrics and Gynecology, Tohoku University School of Medicine, Japan.
Okamura
K
K
Kimura
Y
Y
Watanabe
T
T
Yaegashi
N
N
Murotsuki
J
J
Uehara
S
S
Yajima
A
A
D000818:Animals; D001127:Arginine Vasopressin / Q000097:blood; D001158:Arteries; D001285:Atropine; D002245:Carbon Dioxide / Q000097:blood; D004562:Electrocardiography; D005260:Female; D005312:Fetal Blood / Q000737:chemistry; D005865:Gestational Age; D006340:Heart Rate, Fetal; D006863:Hydrogen-Ion Concentration; D010100:Oxygen / Q000097:blood; D011247:Pregnancy; D012756:Sheep
D001127:Arginine Vasopressin; D002245:Carbon Dioxide; D001285:Atropine; D010100:Oxygen