Fetal and maternal arterial pressures and heart rates: histograms, correlations, and rhythms.

We attempted to shed light on the characterization and control of fetal arterial pressure and fetal heart rate in the chronically catheterized fetal lamb. To do this we continuously recorded fetal and maternal arterial pressures and heart rates as well as amniotic fluid pressures using on-line computer techniques. The data were analyzed for histogram distributions, correlations and regressions, and for intrinsic rhythms within each variable. We found the following: 1) neither fetal nor maternal variables are normally distributed because of an exaggerated mode and frequent skewing to the right, 2) there was no correlation between fetal and maternal variables over time periods of 10 min to 24 h, 3) a positive correlation exists between fetal arterial pressure and fetal heart rate, 4) there were no major rhythms in the fetal or maternal variables or in amniotic fluid pressure with cycles between 10 min and 24 h. The data suggest that 1) fetal arterial pressure and heart rate are largely independent of the mother, 2) fetal and maternal variables are well controlled about a physiological set point, and 3) rhythms in fetal arterial pressure and heart rate are not significant under normal laboratory conditions.