Construction and use of catheter-manometer systems.

The accuracy of invasive arterial blood pressure monitoring is dependent on an adequate damped natural frequency (DNF) and damping factor (DF) of the system. Several factors influencing the DNF and DF were investigated to determine requirements for optimal design of catheter-manometer systems. The frequency sweep method was used in a specially constructed chamber that included linearizing and compensation circuitry. The DNF of isolated 20-gauge cannulae varied from 35.1 to 47.7 Hz. The DNF of 24-gauge cannulae varied from 27.7 to 44.3 Hz. An arterial cannula was found to require a DNF above 40 Hz to prevent the DNF from decreasing to below 25 Hz with the addition of arterial pressure tubing. Arterial pressure tubings exceeding 300 mm in length had DNF values that were unacceptably low even before the addition of arterial cannulae (e.g., the DNF was 23.8 Hz for a 900-mm tubing length, 19.8 Hz for 1,000-mm length, and ranged from 12.9 to 21.4 Hz for 1,200-mm lengths). The 3-way stopcocks and continuous flush devices further decreased the DNF, especially when the diameters were not matched. The percentage decrease caused by 3-way stopcocks and flush devices ranged between 19.5 and 40.8% for 300-mm length tubings and between 2.3 and 25.8% for tubings of 1,200-mm lengths. The radius ratio (outside diameter divided by inside diameter) is introduced as a new method to express the stiffness of arterial pressure tubing.(ABSTRACT TRUNCATED AT 250 WORDS)