Confidence in your research tools
Having the right set of tools for your small animal, invasive pressure studies is essential for building confidence in the quality of the data you are collecting, especially when it comes to long-term studies.
This blog will break down available technologies so that you can ensure you are selecting equipment that will provide you with the accuracy, reliability, and sensitivity that you need. Whether you are familiar with pressure catheters already or just getting started, it’s important to compare the differences between technologies in order to make an informed decision.
Solid-state pressure catheters are the gold-standard for measuring real-time pressure. Fluid-filled (or gel-filled) catheters are a cost-effective and robust alternative. Let’s compare these two technologies to learn more about why having a solid-state sensor in the catheter tip matters for your data.
This article will break down the main differences between the two technologies in the following areas:
- Specifications
- Data Accuracy
- Experimental applications
- Investment
Figure 1: Illustration of a solid-state telemeter pressure recording setup with Kaha. Kaha pressure telemeters utilize wireless power technology integrated with 2 Fr Millar Mikro-Tip® solid-state sensors. The solid-state transducer records pressure right at the tip of the catheter, at the site of interest. In contrast, a fluid-filled pressure transducer transmits the pressure wave through tubing and then into the actual transducer.
Specifications
Transduction Site
It's important to recognize how each sensor works in order to understand how the signal is transmitted.
- Solid-state pressure catheters contain a signal transducer and a MEMS sensor - a silicon chip that flexes with each pressure pulse - within the catheter tip. The sensor is in direct contact with the pressure site.
- Fluid-filled catheters produce indirect measurement, the signal is transmitted through tubing and then into the actual transducer, away from the pressure site.
Care
Cleaning and handling are essential to ensuring equipment fidelity.
- Blood clotting can occur surrounding the solid-state sensor; however, signal attenuation is negligible. Proper device cleaning and careful handling and storage will ensure the device’s longevity.
- Fluid filled catheters possess a gel tip that must be refilled after explant in order to prevent the fluid from washing out and negatively impacting patency. This process is a requirement if you are looking to reuse implants for multiple studies, and requires re-gel syringes for refilling.
Data Accuracy
Accuracy is the primary motivating factor for researchers when choosing to upgrade from a fluid-filled to solid state pressure catheter.
- Solid-state pressure catheters give higher quality data for invasive blood pressure monitoring, measuring directly at the site of interest.
- Fluid-filled catheters measure pressure indirectly, relying on a pressure wave signal transmission through the gel or liquid medium, away from the pressure site.
Attenuation
Figure 2: The advantages of a solid-state pressure sensor at the catheter tip.
A) The position and dimensions of the Millar Mikro-Tip® pressure sensor at the catheter tip of any of the Kaha Sciences pressure telemeters. B) Comparison of blood pressure waveforms recorded using fluid-filled catheters (purple) and the Millar Mikro-Tip® pressure sensor (orange) showing clear attenuation of the blood pressure signal. C) Intracranial pressure waveform recorded using a Kaha Sciences single pressure telemeter (TRM54P) with a 25cm catheter placed in the brain. D) Blood pressure and ECG recording from the same rat 4-days (top) and 48-days (bottom) after implantation of a Kaha Sciences pressure and biopotential telemeter (TRM54PB).
Solid-state pressure catheters offer highly accurate, reproducible, long term pressure measurements. They record sharper peaks and a more pronounced dicrotic notch in cardiac measurements, data typically lost due to the significant signal attenuation of fluid-filled catheters. This resolution is critical for accurate pressure data.
Fluid-filled catheters face signal attenuation and dampening due to bubble formation or changes to gel/fluid properties.
Artifacts
Noise and artifacts can severely distort blood pressure waveform and compromise data quality.
- The pressure waveform recorded by solid-state pressure catheters is unaffected by motion, clotting, gravity, catheter flushing, or catheter bending - given proper cleaning. This means true pressure waveform representation.
- Fluid-filled catheters may incorporate these artifacts into the measured pressure waveform, reducing the reliability of such data and compromising its accuracy.
Phase Shift
Phase shift is detrimental to studies where precise, real-time physiological measurements are needed. This occurs when the pulsatile event and measurement of that event are desynchronized.
- Solid-state catheters are unaffected by phase shift, as they transduce pressure signals directly at the site of interest
- Data recorded from a fluid-filled catheter can be affected by a phase shift. The length of the catheter tubing causes this phase shift, as the pressure signal takes time to reach the blood pressure transducer.
Frequency Response
Frequency response describes the range of frequencies over which the pressure waveform will experience minimal attenuation. In invasive blood pressure studies, the frequency response should be high enough to measure elevated heart rates in your animal model - particularly in rats or mice.
- Solid-state pressure catheters can measure frequency into the kilohertz range without experiencing any signal attenuation.
- Fluid-filled catheters can lose waveform amplitude at higher frequencies, affecting data quality.
Experimental Applications
If you are setting up a new protocol or are interested in upgrading your invasive pressure monitoring equipment, investing in equipment suitable for multiple applications is advantageous for future-proofing your lab.
- The sensitivity of solid-state pressure catheters enables measurement of arterial, venous, ventricular or intracranial pressure.
Fluid-filled catheters generally do not have the sensitivity and signal fidelity for use in non-cardiac research.
Investment
Price is always a factor when choosing the right equipment for your research.
- Solid-state pressure sensors are a premium product, with the data quality to match.
- Fluid-filled catheters are cost-effective, robust, and widely available.
Conclusion: The Benefits of Solid-State Pressure Telemeters
Having a solid-state sensor in the catheter tip matters - upgrading to solid-state pressure technology from a fluid-filled catheter will vastly improve your data quality.
Solid-state pressure catheters are:
- Reusable, given proper care and storage.
- Highly accurate, with reduced waveform attenuation for precise systolic and diastolic pressure measurements.
- Unaffected by artifacts and phase shift.
- Suitable for measuring frequencies in the kilohertz range, with high frequency response for maintaining waveform fidelity in small animal models.
- Used for applications beyond cardiac pressure monitoring, such as intracranial pressure, bladder, and tumor recordings.
OUR RECOMMENDATION:
We recommend Kaha Pressure Telemeters for your long-term invasive pressure studies. Telemetry offers a range of advantages for your research, while providing the unmatched data quality by utilizing solid-state sensor technology. The sensitivity of the solid-state pressure sensor paired with the reliability of the rechargeable telemeter body make this an ideal solution for long-term invasive blood pressure monitoring in rats.
Kaha pressure telemeters incorporate gold-standard Millar Mikro-TipTM catheter technology, containing a solid-state sensor at the catheter tip. This provides you with the ability and confidence to measure highly accurate and sensitive recordings from intracardiac to intracranial pressures.
We offer a range of pressure telemeters to support different application needs - from single pressure or dual pressure, to the combined biopotential/pressure telemeter or sympathetic nerve activity and pressure telemeter. Curious about how these implants look? Get 3D visualization of our pressure telemeters here.
Related Products:
Contact us to discuss which pressure telemeters best suit your research and workflow.
References:
- Illustration by ADInstruments
- Thakkar, P. et al. Hypertensive Response to Ischemic Stroke in the Normotensive Wistar Rat: Mechanisms and Therapeutic Relevance. Stroke 50, 2522–2530 (2019).
- Solid-state vs. fluid-filled pressure catheters: know the difference by ADInstruments
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