The Biomedical Engineering Department of the Johns Hopkins University and DVP, Inc. of Rockville, MD, now InHand Electronics, Inc., have successfully competed and received a Phase II SBIR award from the NIH. The Phase II award to DVP was for developing a Portable Physiological Signal Processor (PSP), a novel device that allows flexible, programmable interface for digital signal processing in a portable unit.

The main purpose of the present project, supported by Maryland Industrial Partnerships Program (MIPS, Contract Agreement # 2209) is to create an innovative and commercially attractive product for cardiac monitoring. It is anticipated that this leveraged funding will allow us undertake the research on the new invention leading to a new product with exciting marketing potential and pave way for a more rapid access to commercialization.

The specific goal of this project is to develop a versatile, easily PROGRAMMABLE CARDIAC MONITOR (PCM) to be used in cardiological practices and for research. The project represents a collaboration between JHU and DVP, Inc.( InHand Electronics, Inc.). On behalf of Johns Hopkins, Dr. Boris Gramatikov is the person responsible for hardware and software development. Mr. Boris Donskoy is in charge on the DVP side. Here are the main issues of the collaboration project:

• JHU will develop ECG amplifiers and data acquisition, and will further research and develop the concept of myocardial ischemia detection using wavelet analysis of ECG signals. JHU will 1) develop a continuous wavelet transform analysis algorithms for ECG signal processing, and 2) demonstrate two applications of the PSP/PCM: i) detection of acute myocardial ischemia in patients presenting to the Emergency Department with chest pain, and ii) detection of ischemia during exercise stress testing.
• DVP, Inc, will further develop the PSP suitable for monitoring ECG signals and collaborate with JHU to implement the ECG signal processing algorithms and implement the wavelet analysis signal processing software. DVP will create a PSP prototype and share it with JHU. DVP will also collaborate on actual prototype development for the applications outlined above.

A PSP prototype has already been developed [2]. The prototype included a motherboard (incl. ADC, DAC), and analog daughterboard, graphic LCD display (340x240 pixels) and a keypad. Two PCMCIA Type II slots are provided. One PCMCIA slot is intended to accept memory application cards. Two full duplex serial communication channels are provided. At present, work is aimed at expanding and improving the existing resources, to create a powerful, turnkey environment for the design of many different physiological instruments. The generic core of the earlier version of the PSP was a 16-bit Hitachi SH7032 RISC processor used as both a system controller and a signal processor [1].

The company is developing an extended version by adding the next generation of RISC technology [3], substantially increasing signal processing capabilities over the existing device. Further, a significant data logging capability is being added which will allow interface to a high capacity memory card or an ATA-type disk drive (through the PCMCIA slot). Such peripherals are currently commercially available in over 20 MB flash memories and 300 MB hard disk drives. These devices are relatively low in cost and, due to their current popularity, are expected to continue becoming more capable and less expensive.

Hardware development

• We studied the various possible options of the "daughter board" to accomodate the ECG amplifiers, the data acquisition and transmission, DC-DC converter and isolation .
• We finalized the data acquisition and data transfer concept, based on the 22 bit Sigma-Delta analog-to-digital converter AD 7716.
• We purchased an evaluation board AD7716EB, which helped us test the AD converters and better design the data acquisition part of the daughter board.
• We completed the amplifier design, based on low-noise instrumentation amplifiers AD 620 and the concept of "driven right leg".
• The JHU partners learned how to work with ORCAD, designed the amplifiers on the daughterboard, and suggested the analog-to-digital circuitry and communication. The DVP team then introduced a series of improvements and finalized the design of the daughterboard.

Parallelizing of tasks:   To avoid unnecessary delay and to make the design more flexible, we decided to split the project into two parallel paths:

a) at JHU:

• development of a support front-end module containing the daughter card (ECG amplifiers, data acquisition using the same AD converter 7716 as the target application), and a communication card to exchange data and control signals with a PC using its parallel port. Thus, software development using the C-language (consistent and platform-independent) could be started well ahead on a PC, before the new OmniMeter [3] design was completed.
• the front-end module also was used to test the DC-DC converter
• The front-end module was placed in a plastic enclosure. A standard Physio-Control ECG clinical grade patient cable was connected to its input, whereas its parallel port was connected to a laptop PC. This configuration was demonstrated during the technical review on April 14, 1999, in front of MIPS representatives. During the presentation, human ECG data were acquired and displayed in real time. Also, the software (please see next sub-section) was run on files from the ST-T Data Base.

• design of a new, much more powerful hardware platform of the basic device, the OmniMeter, now based on a 200 MHz StrongARM SA-1100 processor; this was a revolutionary improvement [3].
• finalized the design of the daughter card, which now accommodates ECG amplifiers, data acquisition, isolation, and fast communication with the main processor of the Physiological Signal Processor. In the second half of April 1999, the company tested some of the main functions of the daughter board in the new device, including ECG amplification and data acquisition (analog-to-digital conversion plus real time graphics display).
• the new design of the Portable Physiological Signal Processor with the newly developed daughter board was shown at the Sensors Expo^TM, Baltimore, May 4 - May 6, 1999.

a) The JHU partners at first developed the real-time model of the Portable Ischemia Monitor as the first targeted application of the Physiological Signal Processor. The software algorithms include (but are not limited to) QRS identification, waves recognition, identification and exclusion of ectopic beats, beat averaging, ST measurement, calculating the Time-Frequency Distribution (TFD) of the signal during the QRS complex by means of the Continuous Wavelet Transform, calculating an appropriate QRS-based ischemia detection index, and a Graphical User Interface (GUI).

b) The JHU partner wrote the Wavelet Transform algorithms in the C-language and tested them on an SGI Indigo workstation. Originally these algorithms had been implemented in Matlab at JHU. Porting onto the Physiological Signal Processor requires C-programming to guarantee fast operation.

c) The JHU partner created an algorithm for contour-plotting in C-language and tested it on a workstation. This algorithm will eventually allow us to plot the time-frequency distributions of the QRS complex on the screen of the portable Physiological Signal Processor (during Phase II).

d) We purchased and installed a Microsoft Visual C++ 6.0 compiler to allow emulation of the algorithms and programs on a PC. Later we will port the software onto the Physiological Signal Processor. We do not anticipate major problems at moving the software onto the OmniMeter, because of the consistency and portability of C-language. The main signal processing algorithms from (a) have been written in C-language and tested. Approximately 90% of the software for morphological analysis of the time signal is finished.

e) With the aim of validating our concepts, we purchased the European ST-T data base (as planned) and started analyzing the data in it. This data base contains 2-hour ECG recordings of ambulatory patients with transient episodes of "silent" (non-symptomatic) ischemia. It comes with a convenient software library which helps the user read the accompanying anotation files and localize precisely the ischemic episodes. So far we have analyzed on a workstation ca. 50% of the data (41 patients), using the wavelet transform algorithms written in C. The analysis confirmed our assumptions that coronary ischemia causes intra-QRS high-frequency changes due to altered cardiac depolarization front. These changes accompany ST alterations and sometimes precede them.

f) To provide a user-friendly PC-based model of the target device we developed a Graphical User Interface (GUI) version of the data acquisition and analysis software using LabWindows^TM (of National Instruments) available at the PI's lab. LabWindowsTM is a versatile C++ language that incorporates many modern GUI features. The LabWindowsTM based software prototype is extremely helpful in many ways. So far it:

· enabled writing and testing of the low-level data acquisition routines (AD conversion using the novel Sigma-Delta 22 bit 2 stage A-D converter);

· helped develop different scroll charts and display graphs for ECG signals and trends with results to be used in the target device;

· helped suggest appropriate functions that will be implemented as touch-screen functions in the portable device;

· test analysis algorithms.

Recently DVP, Inc. decided to use Windows CE as a standard Operating System for the OmniMeter. This not only improves the graphical user interface, but also creates endless new opportunities such as adding TCP/IP interface (wireless or cable), Internet, Data Base Capabilities, Microsoft Office etc.

Some related publications:

[1] Girson, A., Donskoy, B.   Field-programmable instrument highlights application potential of RISC embedded controllers.  EDN, July 3, 1997, pp. 105-107.

[2] Gendreau, P.R.   Team creates PDA that morphs into many variations.   Portable Desig, July 1998, pp.49-56.

[3] Gendreau, P.R.   Spinning 2G configurable platforms challenges designers.   Portable Desig, August 1999, pp.41-46.