Umbilical catheters and arterial blood pressure monitoring.

The natural frequencies, damping coefficients, and accuracies of umbilical artery catheters were determined. The damping coefficients for the 3.5, 5.0, and 8.0 French catheters were 0.40 +/- 0.04 (mean +/- SD), 0.42 +/- 0.05, and 0.19 +/- 0.02, respectively. The natural frequencies were 24.2 +/- 3.2 Hz (mean +/- SD), 18.4 +/- 3.5 Hz, and 26.8 +/- 2.9 Hz, respectively. Measurements obtained with 3.5 and 8.0 French catheters were within 6% of the reference pressure at all pressures and rates tested. With the 5.0 French catheter, however, error greater than 10% from the reference pressure occurred when the rate was 200 pulses per minute or greater and the applied maximum pressure was 100 mm Hg or more.