Abstract

SPAWARSYSCEN has been working collaboratively with LLNL to develop micropower impulse radar (MIR) as a non-invasive tool for monitoring cardiac function in marine mammals. The objective is to provide physiological interpretations of the MIR signals through correlation between known features of the electrocardiogram, cardiac acoustic signature, cardiac ultrasound, respiration and thoracic impedance, and features in the MIR signals.

Critical assessment of cardiac function in dolphins has been unsuccessful because of the inability to employ cardiac catheterization. Lin, Papp and others have shown that microwave techniques provide a simple non-invasive approach for detecting cardiac, arterial wall, respiratory, other physiological movement and volume changes.^1,2,3,4,5,6 Recently, LLNL has developed an entirely new low-cost, low power, range-gated radar sensor technology known as micropower impulse radar that has a wide variety of potential applications. The MIR heart monitor (MIRHM) used in this work has excellent potential to provide information about cardiac and respiratory function in our dolphins that has been impossible to measure previously. It also has great potential as a diagnostic tool to evaluate cardiopulmonary insufficiency or cardiac disease in dolphins.

Applications for this technology with a high likelihood of success include: 1) a hand held or strap-on heart rate monitor for dolphins, 2) a compact, hand-held "stethoscope" which is immune to external audible noise sources, and 3) a non-invasive monitor of fetal heart rates.

Applications for this technology with a high risk, but with high payoff applications include: 1) a non-invasive measurement of relative cardiac stroke volume, 2) non-invasive detection of defects in the heart, 3) non-invasive detection of heart valve malfunctions, and 4) a non-invasive measurement of contractility indices. Using these applications, knowledge gained about cardio-pulmonary deep diving adaptations in dolphins may have potential benefit for other aquatic divers.

MIR devices have very low power output, orders of magnitude lower than a cellular phone, which means that there are no medical side-effects of the device caused by the microwave emissions. These devices also have a low duty cycle, producing pulses on the order of 200 picoseconds in length at a rate of about 2 MHz. The timing between the pulses can be randomized if desired, and this, coupled with the low output power and low duty cycle prevents interference with other electronic instruments such as radios and computers. MIR motion sensors emit bursts of microwaves in the 2 GHz frequency range. They are range gated devices so that the sensitivity can be confined to within a specified distance from the antenna. They detect small changes in the position of any object that reflects microwaves in this frequency range by effectively converting change in position of the object to a change in the amplitude of the reflected pulse.

Among the major advantages of MIR technology are that sensors are very small and lightweight and power consumption is very low allowing the devices to operate continuously for extended periods on a small battery. It is assumed that they can be mass produced at very low cost. Images of dolphin and human MIR tracings will be shown and discussed.

References

1.  Byme W, Flynn P, Zapp R, Siegel M. Adaptive filter processing in microwave remote heart monitors. IEEE Trans Biomed Eng 1986;33(7):717-722.

2.  Chen KM, Misra D, Wang H, Chuang HR, Postow E. An X-band microwave life-detection system. IEEE Trans Biomed Eng 1986;33(7):697-701.

3.  Lee JY, Lin JC. A microprocessor based noninvasive arterial pulse analyzer. IEEE Trans Biomed Eng 1985;32:451-455.

4.  Lin JC, Kiernicki J, Kiernicki M, Wolischlaeger PB. Microwave apexcardiography. IEEE Trans Mtt 1979;27:618-620.

5.  Lin JC. Microwave sensing of physiological movement and volume changes. Bioelectromag 1992;13:557-565.

6.  Papp MA, Hughes C, Lin JC, Pouget JM. Doppler Microwave, a clinical assessment of its efficacy as an arterial pulse sensing technique. Invest Radiol 1987;22:569-573.