A portable electronic unit with no moving parts except button switches digitizes and stores a 48-hour record of the myoelectric activity of the stomach and heart as sensed via electrodes on the surface of the abdomen. Just as the more familiar electrocardiogram (ECG) is useful in diagnosing the condition of the heart, the digital electrogastrogram (EGG) that is also obtained by this portable data recorder is useful in assessing changes in gastric function.

This unit, called the "BioLog," was originally designed to aid studies of gastric changes and related changes in the activity of the autonomic nervous system associated with space motion sickness in astronauts. However the unit can also be used on Earth to collect the same or other types of physiological data from patients who object to the restrictions imposed by traditional stationary physiological monitoring equipment. The unit has a volume of < 1,000 cm3 and a mass of 0.68 kg. It can be mounted on the wearer's belt or attached to the wearer's clothing by use of hook-and-pile fastening material and a custom-designed pocket.

The unit is connected to high-input-impedance, low-output-impedance amplifiers that, in turn, are connected directly (via snap-on fasteners) to the electrodes on the patient's abdomen. This arrangement provides sufficient amplification at the signal source and sufficient immunity to extraneous electrical noise that the signal-to-noise ratio is great enough for ambulatory recording, unlike in older EGG recorders in which ambulatory recording was rendered useless by motion-induced artifacts in the signal.

The EGG can be discerned as a shift in the baseline of the ECG because the characteristic frequencies of the ECG (typically > 1 Hz) are significantly greater than those of the EGG (typically ≈0.05 Hz). The unit digitizes and records the ECG/EGG at a sampling rate of 10 Hz. When the recorded data are subsequently analyzed, they are filtered to separate them into EGG and ECG components.

The unit includes a clock that generates time tags for the data. A 9-V alkaline battery supplies the main operating power. When the main power is off, a capacitor of about 1 farad supplies backup power to keep the clock running for 29 days. A 16-character liquid-crystal device (LCD) displays the current time (in days, hours, and minutes) or other information as needed.

The data-storage medium is a static random-access memory (SRAM) circuit card. The SRAM is structured to enable the recording, within the single data channel, of event markers and other ancillary information time-locked to the ECG/EGG data. The recording of ancillary data involves the insertion of alternate data structures in the data stream. Two types of activity and the associated alternate data structures are accommodated; those that involve suspension of data logging and those for which the data recorded before and after are contiguous in time.

Activities that involve suspension of data logging include turning power on or off, resetting the clock, resetting recording to the beginning of the SRAM (this erases all data recorded previously), and calculation of system resources (battery power and the remaining unused portion of the SRAM). Activities that do not involve suspension of logging include the insertion of event markers by pressing of button switches on the outside of the unit. Five button switches and corresponding event markers are available and can be defined as the user sees fit, without modification of hardware or software. An alternate data structure identifies which event-marker button has been pressed and causes the report of the event to be time-locked to the data that follow. At the moment when an alternate data structure is inserted, the ECG/EGG data are stored in a buffer so that no discontinuity in the data occurs. To prevent activation by accidental contact, an event marker is not inserted until the corresponding button switch has been pressed for 1 second. When the data are subsequently analyzed, the alternate data structures are removed and, in cases of no interruption in logging, the data from before and after are concatenated.

An error code is displayed on the LCD to alert the user to problems with the operation of the unit. There are four error codes; the first indicates that the battery charge is too low, the second indicates that the SRAM card is inserted improperly, the third states the SRAM card is write-protected, and the fourth indicates that the SRAM was not properly initialized. The occurrence of any of these conditions prevents operation.

This work was done by Deborah L. Harm of Johnson Space Center, Gwenn R. Sandoz and Charlene R. Jacobsen of KRUG Life Sciences, and Harve M. Hanish and Marty Loughry of UFI, Moro Bay, CA. For further information, access the Technical Support Package (TSP)free on-line at www.techbriefs.com/tsp under the Electronics & Computers category.

In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to

KRUG Life Sciences, Inc.
1290 Hercules, Suite 120
Houston, TX 77058

Refer to MSC-22677, volume and number of this NASA Tech Briefs issue, and the page number.

NASA Tech Briefs Magazine

This article first appeared in the July, 2000 issue of NASA Tech Briefs Magazine.

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