 DSI Pressure SensingTechnologies in Small Animal Chronic Monitoring Applications PDF Download |
DSI Pressure Sensing Technologies in Small Animal Chronic Monitoring Applications
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 physiol-ogic monitoring. It’s why DSI telemetry products are rou-tinely used by virtually all of the world’s top drug developers and academic research centers.
With regard to blood pressure measurement, DSI capabilities are referenced in AHA Blood Pressure Measurement recom-mendations as a “…powerful methodology for investigating short-term and long-term regulation of BP and its variabil-ity.”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 which were previously impossible.
Dual-Pressure Recording Offers a More Comprehensive Physiological Assessment
The world’s first high fidelity dual-pressure wireless monitor-ing device for small animals: the DSI HD-S21transmitter (Figure 1). The HD-S21 is designed as a research tool for chronic monitoring of two pressure signals as well as biopo-tential (e.g. ECG), temperature and activity parameters. For instance, simultaneously collect left ventricular and blood pressure recordings. The HD-S21 brings large-animal moni-toring technology to small animals by leveraging materials previously used only for recording LVP in large animals. The result is a device that accurately senses parameters requiring improved frequency response—such as dP/dt.
DSI’s High-Performance Pressure Sensing
DSI developed the first fully-implantable transmitter 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 proprie-tary and highly biocompatible catheter to acquire the signal. After twenty years and countless improvements, more than 10,000 DSI pressure transmitters 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 grow-ing number of customers desiring to use pressure sensing technologies to record signals that require even more fre-quency response, for applications such as LVP in large and small animal species, DSI responded by designing new pres-sure sensing systems with improved accuracy and stability.
Low Pressure-Drift Even Over Long Studies
Peer-reviewed journals cite the proven performance charac-teristics of DSI pressure-sensing products for measuring chronic blood pressure, with many customers routinely us-ing our transmitters for several months in the same animal.M2,3 Our stable sensors allow for very low pressure drift and are able to identify even subtle blood pressure variations.4 Historically, DSI pressure sensing systems exhibited drift rates of less than 2-3 mmHg/month depending on the trans-mitter model. Now, new proprietary DSI designs and materi-als demonstrate even lower drift rates (Figure 2) while main-taining the superior long-term biocompatibility necessary for chronic in vivo function.
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.
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.
Figure 3. DSI Small Animal 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 materi-als in vessels and other physiological environments dem-onstrates the catheters are appropriate for long-term re-cordings without signal degradation.
Minimize Bubbles. Maximize Frequency-Response.
Traditional fluid-filled catheters, such as those used with external Statham type transducers, are capable of devel-oping air pockets that can significantly compromise frequency response. These bubbles often result fromdesorption 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 trans-ducer. This long length results in limited frequency re-sponse performance and/or phase shift in the pressure signal. In contrast, DSI catheters are designed with rigid polymer materials, and, because they are fully implanted, require much shorter lengths. Our unique thin-walled catheter tip promotes superior transfer of frequency con-tent through a gel interface.
DSI catheters demonstrate high fidelity frequency re-sponse 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.5
Furthermore, DSI catheters adequately capture rele-vant pressure waveform frequency content for the range of heart rates of interest as displayed in figure 5 by showing no attenuation in the pressure amplitude(Figure 5).
Accurate Dynamic Pressure Waveform Reproduction
To accurately reproduce any waveform, frequency response must be at least two times greater than the highest frequency component within the signal.6 Though there are higher frequency components than the heart rate, 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.7 This same rule does not apply for good reproduction of a left ventricular pres-sure waveform. 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 fre-quency response in excess of 15 times the typicalheart rate of a rat (>100Hz at -3dB) and has been demonstrated to offer equivalent performance to a Millar catheter in controlled comparisons of sys-temic pressure signals (Figure 6). The same catheter also offers highly com-parable performance to Millar when recording left ventricular pressure signals and associated dP/dtmax under control (Figure 7) and challenge (Figure 8).
The Configuration You Need
Superior performance with our pressure sensing catheters is provided by a variety of sizes and lengths for your varied applications and desired catheter place-ments. 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 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.
2Brooks D, Horner RL, Kozar LF, Waddell TK, Render CL, Phillipson EA. Validation of a telemetry system for long-term measurement of blood pres-sure. J. Appl. Physiol. 1996; 81(2):1012-1018.
3El-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.
4Van 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.
5Main, Bradley. “Cardiovascular Safety Evaluation: Left Ventricular Pressure Measurement in Dogs, Monkeys and Rats.” Eli Lilly and Co. Indianapo-lis, IN USA. Presented during Advanced Topics in Cardiovascular Assessment during 6th Annual Meeting of the Safety Pharmacology Society. Slide 16. 25 September 2006
6H. Nyquist, "Certain topics in telegraph transmission theory," Trans. AIEE, vol. 47, pp. 617-644, Apr. 1928
7Geddes, L.A. “Handbook of Blood Pressure Measurement.” Clifton: The Humana Press, 1991.