Blood velocities in the dorsal pedis and radial arteries during labour.

To detect evidence of aortic compression by the uterus in the supine position during labour, blood velocity in the dorsal pedis artery was recorded using Doppler ultrasound. Twenty-seven women in labour, 16 with an epidural block (epidural group) and 11 with painful contractions (non-epidural group) were studied through several contractions in the lateral and supine position. In the non-epidural group, blood velocities showed large fluctuations, typical of temperature regulation, between contractions. During contractions, velocities were reduced by 80% in both positions, most likely due to vasoconstriction caused by pain. Radial artery measurements illustrated the same fluctuations between, and reductions during, contractions. In the epidural group, blood velocities were steadily high without fluctuations between contractions, illustrating sympathetic nerve blockade. In 14 of the 16 women, velocities remained high during contractions; in the remaining two women velocities decreased, mainly in systole, during contractions in the supine but not in the lateral position without concomitant fetal heart rate pathology.