DSI Pressure Sensing Technologies

Innovation Built on a History of Performance

Expect innovation from a firm with a solid history of high-performance reliability. Delivering quality, dependability, and superior performance has been fundamental to DSI’s wide acceptance as the “gold standard” for chronic physiologic monitoring. It’s why DSI telemetry products are routinely used by virtually all of the world’s top drug developers and academic research centers.

With regard to blood pressure measurement, DSI’s capabilities are referenced in the American Heart Association Blood Pressure Measurement recommendations as a “…powerful methodology for investigating short-term and long-term regulation of BP and its variability.” 1 The advent of DSI
pressure sensing technology with best-in-class chronic sensor stability, biocompatibility, and easier surgical deployment has allowed scientists to conduct chronic telemetry studies that were previously impossible. 

DSI’s High-Performance Pressure Sensing

DSI developed the first fully-implantable telemetry device with a chronic pressure sensing capability in 1989 for systemic blood pressure measurement in rats. DSI pressure sensing systems consist of a solid state sensor coupled to a proprietary and highly biocompatible catheter to acquire the signal.  After twenty years and countless improvements, more than 10,000 DSI pressure implants are used annually to record blood pressure data, plus other cardiovascular and non-cardiovascular pressure signals in rats, mice, rabbits, dogs, pigs, non-human primates and other species.  With a growing number of customers desiring to use pressure sensing technologies to record signals that require even more frequency response, for applications such as LVP in large and small animal species, DSI responded by designing new pressure sensing systems with improved performance and stability.  

Dual-Pressure Recording Offers a More Comprehensive Physiological Assessment

DSI developed the world’s first high fidelity dual-pressure wireless implant for small animals: the HD-S21 (Figure 1).  The HD-S21 is a research tool designed for chronic monitoring of two pressure signals as well as biopotential (e.g. ECG), temperature and activity parameters in rats and similarly sized animal models. For instance, simultaneously collect cardiac left ventricular pressure (LVP) and arterial blood pressure recordings. Leveraging a pressure sensing technology originally designed for large animal monitoring, DSI adapted this technology to provide the frequency response and sensitivity to accurately detect parameters such as dP/dt, in small animals. 2

HD-S21

 

Low Pressure-Drift Even Over Long Studies

Peer-reviewed journals cite the proven performance characteristics of DSI pressure-sensing products for measuring chronic blood pressure, with many customers routinely using our implants for several months in the same animal. 3, 4  Our stable sensors allow for very low pressure drift and are capable of identifying even subtle blood pressure variations. 5 Historically, DSI pressure sensing systems exhibited drift rates of less than 2-3 mmHg/month depending on the implant model. Now, proprietary DSI designs and materials demonstrate even lower drift rates (Figure 2) while maintaining the superior long-term biocompatibility necessary for chronic in vivo function. 

Drift 

Optimized Catheter Design
Proven Biocompatible Catheter Materials: Convenience and Chronic Patency

Each DSI catheter has a thin-walled sensing region at the tip containing a proprietary gel to interface between the catheter fluid and the surrounding body fluid (Figure 3). This interface allows for chronic catheter patency without the need to use an anticoagulant or flush the catheters. 

Catheter

 

DSI catheters are made from a medical grade polymer. Our catheter tips are treated using a proprietary process that eliminates surface defects and maximizes in vivo patency. Extensive chronic testing of our catheter materials in vessels and other physiological environments demonstrates that the catheters are appropriate for long-term recordings without signal degradation.  

Minimize Bubbles. Maximize Frequency-Response.

Traditional fluid-filled catheters, such as those used with external Statham type transducers, are capable of developing air pockets that can significantly compromise frequency response. These bubbles often result from desorption of the catheter fluid (typically water/saline). DSI catheters contain a non-compressible fluid designed to minimize absorption of air and therefore minimize desorption. 

Mechanical Design Properties of Catheters Optimize Frequency Response

Although adequate for routine systemic blood pressure measurements, traditional fluid-filled catheters connected to remote pressure transducers have historically provided modest frequency response. A traditional catheter is often constructed of compliant materials, like silicone, with a relatively long catheter length extending to the transducer. This long length results in limited frequency response performance and/or unacceptable phase shift in the pressure signal.  In contrast, DSI catheters are designed with rigid polymer materials, that are still flexible and able to be easily manipulated, and, because they are fully implanted, require much shorter lengths. Our unique thin-walled catheter tip promotes superior transfer of frequency content through a gel interface.

DSI catheters demonstrate high fidelity frequency response values in excess of 100Hz at -3dB (depending on catheter configuration, Figure 4), which is appropriate for even the most demanding applications such as measuring dP/dtmax from  LV pressure waveforms. dP/dtmax values of nearly 16,000 mmHg/sec have been confirmed accurate.Furthermore, DSI catheters adequately capture relevant pressure waveform frequency content for the range of heart rates of interest as displayed in Figure 5 by showing no attenuation in sine wave amplitude

Figure 4

 

Comprehensive Support Tools

DSI has developed tools to aid customers using
pressure-sensing catheters, including:

  •  Re-gelling instructions
  •  Tools for handling catheters during surgery
  •  Surgical manuals and videos  

Accurate Dynamic Pressure Waveform Reproduction

When using a digital system to accurately reproduce any waveform, the sample rate must be at least two times greater than the highest frequency component within the signal. 6,7 Geddes has validated that a frequency response of six times the heart rate (highest cardiac frequency) allows for good reproduction of an arterial blood pressure waveform, (this same rule does not apply for good reproduction of a left ventricular pressure waveform). 8 For a rat with a heart rate of 360 BPM, the main frequency content is 6 Hz, therefore good reproduction of the arterial blood pressure waveform would require a frequency response of 36 Hz. Our most recently developed 8 cm rat catheter has a frequency response in excess of 15 times the typical heart rate of a rat (>100Hz at -3dB) and has been demonstrated to offer equivalent performance to a Millar catheter in controlled comparisons of systemic pressure signals (Figure 6).  The same catheter also offers highly comparable performance to Millar when recording left ventricular pressure signals and associated dP/dtmax under control (Figure 7) and challenge (Figure 8 ).  Frequency analysis of LVP signals from chronically instrumented dogs, nonhuman primates and normal rats confirms that all important information in those signals occurs at frequencies below  approximately 100 Hz (Figure 9).  A higher frequency response than necessary adds no value, uses additional resources and can in some cases be harmful with digital acquisition systems if any significant high frequency noise is present in the system. 6,7  

Output signal from three pressure sensing systems.


Blood Pressure

The Configuration You Need

Superior performance with our pressure sensing catheters is provided by offering a variety of catheter sizes and lengths for your varied applications and desired surgical placements. Catheters range from 1.3 French (0.42 mm) to 4.2 French (1.4 mm), in lengths from 5 to 35 cm. Custom tip lengths are available to suit specialized applications such as ocular pressure, aortic pulse wave velocity and bladder pressure. Suture aids assist with secure attachment to the wall of the heart or other organs. 



Your Expanding Portfolio of Research Tools

As novel research applications come into mainstream use—both cardiovascular (e.g. left ventricular, systemic arterial and pulmonary arterial pressures) and non-cardiovascular (e.g. pleural or bladder pressures)—DSI continues to expand its portfolio of support tools and proof sources to help you adopt and succeed with new research procedures. Don’t trust your important research to anything less than the proven research leaders: DSI.  


 

1Kurtz TW, Griffin KA, Bidani AK, Davisson RL, Hall, JE.  Recommendations for Blood Pressure Measurement in Humans and Experimental Animals.  Part 2: Blood Pressure Measurement in Experimental Animals.  Hypertension.  2005; 45:299-310.
2Sarazan, R.D., Mittelstadt, S., Guth, B., Koerner, J., Zhang, J. and Pettit, S.  Cardiovascular Function in Nonclinical Drug Safety Assessment: Current Issues & Opportunities.  Perspectives from the Health & Environmental Sciences Institute (HESI).  International Journal of Toxicology, 30(3):272-86. 2011 3Brooks D, Horner RL, Kozar LF, Waddell TK, Render CL, Phillipson EA.  Validation of a telemetry system for long-term measurement of blood pressure.  J. Appl. Physiol.  1996; 81(2):1012-1018.
4El-Mas MM, Abdel-Rahman AA.  Longitudinal studies on the effect of hypertension on circadian hemodynamic and autonomic rhythms in telemetered rats.  Life Sciences.  2005;76:901-915.
5Van Vliet BN, Chafe LL, Antic V, Schnyder-Candrian S, Montani JP.  Direct and indirect methods used to study arterial blood pressure.  Journal of Pharmacological and Toxicological Methods.2000 (44) 361-373.
6Sarazan, R.D., Kroehle, J.P. and Main, B.W.  Left ventricular pressure, contractility and dP/dtmax in nonclinical drug safety assessment studies.  Journal of Pharmacological and Toxicological Methods, 66:71-78. 2012
7H. Nyquist, "Certain topics in telegraph transmission theory," Trans. AIEE, vol. 47, pp. 617-644, Apr. 1928
8Geddes, L.A. “Handbook of Blood Pressure Measurement.”  Clifton: The Humana Press, 1991.