The Dynamic Responses of Liquid-filled Catheter Systems for Direct Measurements of Blood Pressure

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Abstract
Direct measurement of blood pressure with a fluid-filled catheter and transducer is widely accepted in clinical practice. Errors associated with the measurements are often not appreciated. The system frequently is unable to reproduce rapidly changing waveforms and overshoots to produce higher peak pressures. The most common causes of this phenomenon are small trapped air bubbles and long connecting tubing. To assess the inaccuracy in pressure measurements, the weighted sum of the percentage difference between reference and recorded amplitudes of sinusoidal waveforms was calculated for several catheters and connecting tubings. When the connecting tubing was shorter than 3 ft long and no air bubbles were trapped, readings were accurate. Connecting tubings 7 ft long or longer, and/or air bubbles, were frequently associated with inaccurate results. Minimal air bubbles (0.25 ml) in a system exaggerated the systolic pressure measurement by 41 torr when simulated blood pressure was 150/50 torr.

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