DYNAMICS OF CARDIOVASCULAR-RESPONSES TO REPEATED PARTIAL UMBILICAL-CORD COMPRESSION IN LATE-GESTATION SHEEP FETUS

We characterized the detailed hemodynamics of fetal blood pressure, he art rate, common umbilical blood flow, and femoral blood how responses to partial compression of the umbilical cord and tested the hypothesi s that repeated cord compression modulates fetal cardiovascular respon ses in 10 chronically instrumented fetal sheep at similar to 130 days of gestation. In five fetuses (group I), partial compression of the um bilical cord was induced 12 times, each for 5 min at 15-min intervals. Each cord compression reduced common umbilical blood flow by 50% and produced modest falls in fetal pH (7.33 +/- 0 to 7.29 +/- 0) and arter ial PO2 (21.1 +/- 0.2 to 16.8 +/- 0.2 mmHg) and a mild increase in art erial PCO2 (49.9 +/- 0.5 to 54.9 +/- 0.4 mmHg). Sham experiments were performed in five other fetuses (group II). Second-by-second analysis of group I fetal cardiovascular data revealed a clear biphasic respons e to partial cord compression. Phase I (1st min of cord compression) w as characterized by a rapid bradycardia and a rapid femoral vasoconstr iction (primary response); phase II (minutes 2-5 of cord compression) was characterized by a delayed bradycardia and a return of femoral vas cular resistance toward baseline (secondary response). Repeated cord c ompression abolished the primary, but not the secondary, cardiovascula r responses. These results demonstrate that fetal cardiovascular respo nses to stress may be modified by preexposure to repeated intrauterine challenges.