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Solid-State Sensors vs. Fluid-Filled Transducers
Accurate detection of blood pressure is perhaps the most crucial parameter in any study requiring an indication of cardiac function. In the research laboratory, pressure measurement techniques fall under two broad classifications: direct and indirect methods. Indirect methods, such as the Cuff Technique can be used to measure systemic blood pressure; however, these methods are approximate and cannot detect diastolic pressures accurately.
Direct pressure sensing devices offer a precise and meaningful measure of blood pressure and, as the name suggests, are able to detect pressure at the source. These devices are typically inserted (as part of a catheter) through the carotid artery or femoral artery until the sensor is located in the region of interest such as the ventricle or aorta. Solid state sensors, available from Scisense, are mounted at the tip of the catheter and measure pressure precisely and with a high degree of frequency response directly at this location. Alternatively, fluid-filled transducers rely on a liquid-filled tube to transmit pressure from the region of interest back to an external pressure sensor.
The Scisense Advantage:
The figures below show the difference in quality and accuracy of pressure detection between a Scisense solid state sensor and a conventional* fluid-filled sensor. Notice that the fluid-filled transducer is unable to accurately detect changes in pressure at higher frequencies. The signal becomes grossly distorted at a frequency of 5 Hz (approximately 300 BPM) and unrecognizable at 10 Hz and 15 Hz. In addition to measuring precise and noise-free pressure signals, solid-state transducers allow for accurate detection and calculation of dP/dt, considered to be one of the most fundamental indices of cardiac function.
Furthermore, Scisense solid-state sensors are a user-friendly choice, as they do not require cumbersome and time-consuming flushing to remove air bubbles, nor do they involve a complicated system of tubing and stopcocks. Accuracy, reliability, and efficiency are Scisense advantages.
Explanation of graph (above):
Signal Integrity:
- Square wave produced by a signal generator is accurately represented by the Scisense pressure catheter
- Signal is distorted when measured by fluid-filled transducer
- Above 4Hz (equivalent to heart rate of 240 BPM), the square wave is no longer recognizable with the fluid-filled sensor
Frequency Response:
- Pressure amplitude is unaffected for Scisense transducer at higher frequencies but not the fluid-filled transducer
- At high frequencies, fluid-filled transducer cannot detect pressure changes accurately
- Fluid-filled catheters require constant flushing as frequency response is affected by introduction of air bubbles into the fluid-filled system (catheter, stopcocks, tubing)
Other Benefits to Scisense Solid-State Pressure Sensors:
dP/dt:
- Accurate detection of peak negative/positive dP/dt is dependent on true representation of pressure
- Because of poor frequency response and high signal distortion, accurate dP/dt will likely not be possible with fluid-filled sensor
Signal Artifact:
- Fluid-filled catheters are prone to whip and impact artifacts, while Scisense solid-state transducers are not affected by motion
Ease of use:
- Fluid-filled catheters require constant flushing as frequency response is affected by introduction of air bubbles into the fluid-filled system (catheter, stopcocks, tubing)
Calibration and balancing:
- Scisense catheters are calibrated and balanced at any level prior to insertion, fluid-filled transducers require precise positioning when being calibrated
Summary of benefits:
- Measure pressure at the source
- Signal integrity
- Frequency response
- Impervious to motion artifact
- Sensitivity (10 μV/V/mmHg)
- Ease of use
- No flushing to remove air bubbles
- No stopcocks, tubing, etc.