Triton ARTē Evaluated By Air Force
Sonomicrometry in the NMR Environment
Advances In Data Acquisition And
Analysis What's New? Triton ARTē Evaluated By Air Force
Sonomicrometry in the NMR Environment
Advances In Data Acquisition And
Analysis What's New?
The Laboratory for Aerospace Cardiovascular Research (LACR), within the Armstrong Lab, located at the Brooks Air Force Base in San Antonio, Texas is one of the Air Force's four "superlabs". As its name indicates, LACR is the nation's center for excellence in cardiovascular research aimed at better understanding and protecting the human in airborne and space systems. The laboratory has a number of interservice and interagency cooperative links. Under the leadership of Army Col. Ricky Latham, MD, this lab has developed a number of models for zero-G and high-G stress cardiovascular response.
The hypergravity model is centered around an instrumented baboon (papio anubis) in a controllable centrifuge. The surgery team, led by Col. John Fanton, MD, has wide experience implanting advanced transducers including flow cuffs, sonomicrometer crystals and Konigsberg micromanometers. This instrumentation provides real-time information on cardiovascular performance during the centrifuge exposure. The microgravity experiments are performed in parabolic flights of a specially equipped KC-135 aircraft. The descent portion of the parabolic flight provides an apparent zero-G environment in which subjects and investigators float within the airplane.
In a recent article (Am. J. Physiol, 265:H244-H251, 1993) investigators at LACR reported on the effect of upright tilt on ventricular/vascular coupling in chronically instrumented baboons. The motivation for the study was the need to understand central circulatory hemodynamics in altered gravity states. To this effect mature baboons were instrumented for measurement of electrocardiogram, aortic root flow, aortic pressure, left atrial and left ventricular pressures and left ventricular volume. This complex instrumentation was achieved with the aid of an electromagnetic flow probe, specially modified Konigsberg pressure transducer and sonomicrometry equipment from Triton. In particular, the left ventricular volume (LVV) was computed from real-time measurements of septolateral, anteroposterior and base apex dimensions provided by a multi-channel Triton sonomicrometer. In preparation for future chronic studies of this nature, Cap. Steve Koenig, in collaboration with Prof. Dan Ewert of the University of North Dakota, are evaluating blood flow measurement instruments. To this effect, steady state and pulsatile flow chambers have been manufactured to compare candidate technologies with previous EMF probes and calibrated standards. In this process, Triton's active redirection transit time (ARTē) flowmeter was recently tested. The results in the flow benches demonstrated ARTē accuracy and sensitivity. Following these tests, a 12 mm probe was used around the aortic root of a rhesus monkey. The pulsatile flow measurement baseline proved to be perfectly stable over a range of pressures obtained by injection of a hypertensive agent. Furthermore, cardiac output determination by the traditional thermodilution method agreed extremely well with the mean flow reading of the Triton ARTē unit.
By: Roger Rehr, M.D.
Our interests are in defining the relationships between regional cardiac metabolism and mechanical function in the open-chested dog with LAD occlusion; this model was chosen because of the huge amount of published experience with it. Our metabolic studies include serial 31P NMR spectroscopic measurements (Bruker Biospec) with a surface coil placed on the heart during coronary occlusion and reperfusion. During these NMR measurements of ischemic zone metabolism, we simultaneously monitor mechanical function in this region (wall thickening or segmental shortening, depending on the protocol) as well as in a distant, non-ischemic region using a Triton Technology sonomicrometer. (Triton Technology)
Obtaining the NMR measurements require an environment free of RF noise at the Larmor frequency of the nucleus of interest; for 31P in our system this is 40 MHz. There are two sources of RF noise introduced by the addition of the sonomicrometer to the NMR system: (1) harmonics produced by the sonomicrometer itself, and (2) ambient RF noise which is picked up from the laboratory environment by the sonomicrometer leads and carried into the magnet ('antenna effect'). In our lab, either one of these is sufficient to obliterate the NMR signal, but the effects of both can be virtually eliminated. Each NMR acquisition is gated so as to be acquired at end-inspiration via a microswitch/cam assembly mounted on the animal ventilator. This assembly also triggers a monostable multivibrator with a time constant of just over a second; the multivibrator pulse turns off the sonomicrometer clock during the one second in four when NMR data is actually being acquired, and thus eliminates the first source of RF noise. We have eliminated the antenna effect by (l) using double shielded twinaxial cables (Alpha 9814) between the sonomicrometer and the magnet, (2) installing an aluminum bulkhead on the face of the magnet through which all connections are made. and (3) routing our cables over a copper mesh ground plane installed along the floor between our magnet and equipment rack.
We currently experience no degradation of the 31P NMR signal by insertion of the sonomicrometer leads and apparatus into the system, and operation of the NMR spectrometer produces no degradation of the sonomicrometer signal. I would be happy to provide a more detailed account of (1) the gating electronics and their connection to the sonomicrometer, (2) the design of our bulkhead, or to answer any questions regarding the marriage of the sonomicrometer and NMR spectroscopy. Please contact Triton for contact information.
The CORDAT II data acquisition and analysis system which Triton/DISS introduced at AHA in 1992 is now gaining wide acceptance in the US and Europe. CORDAT II eliminates the need for the conventional polygraph in your laboratory. Integrated with the Branch Laser Chart software, it provides on-line validated hard-copy of the physiological signals using a laser printer. Signals can be re-drawn with Laser Chart replay using variable chart speed and scales on a Hewlett-Packard LaserJet 4 printer. A recent IEEE publication (Computers in Biology and Medicine, Skyschally et al.) presented the design and validation of the system and its algorithm. Since the writing of that paper, a number of new features--most of which were suggested by our users--have been developed and added to the current release.
Here are some of the exciting new capabilities which CORDAT brings to your lab:
Please contact Triton for a complimentary reprint of the IEEE article describing the CORDAT system.
Continued search for improvements in the Dye-Trak microsphere sample processing technology has led to two new membranes developed by Nuclepore and Poretics. The membranes originally reported by Kowallik et al. were 8 micron-pore size (Nuclepore part number 180614). Now 25 mm filter disks are available in 10 micron pore sizes. They still retain the microspheres, while allowing improved flow-through of the digested tissue samples.
1. Part 31079--10 microns, 200,000 pores per square centimeter (Poretics).
Triton Technology's exclusive Active Redirection Transit Time flow probes are now available in four new smaller sizes. These are:
PART: SIZE:
200-306A 6 mm lumen
200-306B 7 mm lumen
200-306C 8 mm lumen
200-306D 9 mm lumen
A new enclosure chassis--known as the Twin Pack (part number 200-198) has been added to the System 6 instrumentation family. This provides investigators with a compact 2-channel housing for the ART2 flowmeter and either of Triton's two pressure and dP/dt modular instruments.
Physiologists working with long term chronic preparations require a variety of esoteric devices which are not always easy to find. Triton is happy to provide referrals for such implements as we discover high quality sources for them. Such is the case of Freedom Research Instruments' line of animal research jackets for post-operative and experimental use. The durable jackets are designed to provide the animal with as comfortable an environment as is feasible. The jackets are form-fitting polyester or nylon mesh and nylon/spandex torso or full length suits that zip on and self-adjust to the animal's contours. They are outfitted with Cordura nylon pockets that are attached to the side of the torso to house instruments or cables and have a reinforced "button hole" to facilitate the passage of catheters and cables to the inside of the jacket. When studying dogs, use of these jackets combined with optional anti-chew collars provides an effective protective system.
The current line of torso jackets for large animals and dogs has two styles of construction. The main difference between the two is in the placement of the stretch panels. One places the panels on each side of the dorsally located zipper. The other has the stretch material located in the chest and abdominal area. The latter is recommended for applications requiring the pockets to carry heavier loads. As all standard jackets come complete with two pockets, you should specify the dimensions of the contents.
Swine jackets are similar to dog jackets, but larger in the neck area. Since swine tend to gain weight and size mostly circumferentially, users have been able to add optional expansion panels which zip in between the existing zippers extending the use time of a smaller jacket. Thus, the jacket simply grows with the animal.
Primate jackets are designed to prevent the subject from tampering with the instruments, yet remain comfortable. The same technique of incorporating stretch material into the jacket construction provides for good fit. Back-pack mounting of the instrument pocket, with an additional Cordura nylon pack cover, provides for security from curious fingers. Rodent and rabbit jackets range from torso jackets for infusion/tether work to full length designs. Standard jackets are currently available for the following species: dogs, swine, sheep, primates, rabbits, guinea pigs, rats. In addition to Freedom's standard line of jackets, they can also design and manufacture custom jackets and harnesses for special applications or unusual species.
When using a canine model for research studies, the natural tendency of the post-op subject is to lick the surgical incisions and bite at catheters, cables, and jacket. To help protect the instrument pouches and animal from damages due to biting and chewing, Freedom has developed a new foam-core neck brace/collar. It limits the range of extreme head movement while remaining comfortable and allowing normal feeding and sleeping activities, unlike large, stiff Elizabethan collars. In addition, current users report that the collar is tolerated very well with almost no break-in period required. When the dog twists it's head around to bite at the jacket, the 2-inch thick foam core compresses between the skull and the shoulder and stiffens up, restricting range of motion. The foam is covered by a washable, zip-on Cordura nylon casing and adjusts/closes at the back of the neck with Velcro and a strap with a quick-release ladder lock plastic buckle. It can be used alone, or secured to the neck of a jacket using the two ladder lock buckles and straps or fasteners such as plastic cable ties.
This collar concept can also be used with other species which are prone to chewing such as sheep, goats, and other ruminating animals.
For information on reaching Freedom Research Instruments, please contact us via fax at: 619-272-1451 or our toll-free support line (800) 872-1251.
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Baumgart, D., Ehring, T., Kowallilk, P., Krackar, M., Heusch, G., Impact of alpha-adrenergic Coronary Vasoconstriction on the Transmural Myocardial Blood Flow Distribution During Humoral and Neuronal Adrengergic Activiation. Circulation Research 73:869-886, 1993
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Copyright 1995 Triton Technology, Inc.
Updated May 29, 1998