Technology Commercialization Opportunity

Implantable Biotelemetry System for Preterm Labor and Fetal Monitoring

Objective

The Fetal Treatment Center (FTC) at UC San Francisco has developed a revolutionary surgical procedure to treat fetuses suffering from diaphragmatic hernia, a condition in which a hole in the diaphragm allows internal organs to shift from the abdominal cavity into the chest cavity. The lungs have insufficient space to develop and about 60 percent of children born with this condition die. The FTC first used traditional hysterotomy surgery to correct this anomaly. They recently developed a minimally invasive procedure using endoscopic techniques, called "FETENDO." A 10mm trocar is used to allow in-utero surgery on the fetus with a laser scalpel. This approach was chosen to minimize postoperative preterm labor, a problem that is encountered in all patients who undergo fetal surgery. Accurate monitoring of uterine contractions in the postoperative period is critical to develop medications that can inhibit the progression of preterm labor.

In 1993, The FTC established a relationship with Sensors2000! (S2K!) to adapt NASA's implantable biotelemetry devices to their monitoring needs of the human fetus and its uterine environment. One of their major goals was to measure intra-uterine pressure changes in order to monitor and treat preterm labor. S2K! used NASA's technology to design a system that could accurately measure intra-uterine pressure changes, body temperature, and the heart rate of the fetus. While the first system was based on a commercial sensing device, NASA's recent efforts have been focused on a pill-sized transmitter that is small enough to be introduced into the uterus through a 10mm trocar.

During Endoscopic Fetal Surgery a trocar is inserted into the womb to gain access to the fetus. The small size of our Pill Transmitter makes it possible to place it into the womb through a trocar of 10mm diameter.

Product Profile

The current biotelemetry system monitors pressure and temperature and consists of four major building blocks ­ implantable pressure/temperature transmitter, biotelemetry receiver, data acquisition card, and digital signal processing system. The transmitter uses Pulse Interval Modulation (PIM) to send temperature and pressure information out of the biological environment (the uterus in the example described above). The RF carrier frequency is in the biomedical range (174 - 216MHz). A pair of RF bursts (pulses) is transmitted at a frequency of about 1-2Hz. The interval between successive pulse pairs is proportional to the measured temperature. The interval between the two pulses of a pair is proportional to the sensed pressure. The low data rate is sufficient for monitoring intra-uterine contractions, which occur over several minutes. The transmission range is 3 to 10 feet, depending on the position of the transmitter in the body and its biological environment.

Pressure/Temperature Transmitter

A prototype of the transmitter has been built on a printed circuit board (PCB) using surface-mount components and is currently being tested in sheep. The dimensions of the PCB prototype are small enough to allow implantation in the uterus of a pregnant sheep. The entire transmitter is encapsulated in biocompatible silicone rubber. Power is supplied by two silver-oxide batteries. The average power consumption of the current design is less than 40 microW., which yields a lifetime of approximately 4-6 months. Temperature is sensed by a thermistor and pressure by a solid-state, piezoresistive pressure transducer. Absolute pressure readings are not required, only changes in pressure (typically 40-60 mmHg) are of interest in monitoring preterm labor.

The final "pill" version of the transmitter is small enough to fit through a 10mm trocar. The circuits of the PCB prototype and of the pill transmitter are identical. The pill, however, uses Chip-on-Board technology (COB) to drastically reduce the size of the printed circuit board from 38 x 28 mm to 22 x 8 mm. Unpackaged dies are flip-chip bonded directly onto the printed circuit board, along with surface mount resistors and capacitors. A pressure transducer die is rebonded to the PCB. The batteries and the PCB are placed into a pill-shaped shell, which is then encapsulated in biocompatible silicone.

Biotelemetry Receiver

The receiver is a stand-alone unit that converts the pulse interval modulated RF signal into a digital pulse stream, which is then decoded into voltages proportional to temperature and pressure. The RF portion consists of a Konigsberg receiver module TR8 that has been modified to demodulate low-frequency PIM signals. The digital output signal of the TR8 is then processed by the decoder. The decoder extracts and integrates the two pulse intervals that contain information on pressure and temperature. Sample-and-hold amplifiers convert the integrator outputs into analog voltages. The sensitivity of the temperature channel is 10mV/C, and of the pressure channel 1mV/mmHg.

Data Acquisition and Signal Processing System

The data acquisition system is based on LabVIEW, a graphical programming language for virtual instrumentation. The current system uses a PCMCIA card to digitize the analog pressure and temperature data from the biotelemetry receiver into a laptop computer where it is processed by the LabVIEW, software. The program displays and stores the data as a function of time, it also performs peak detection and determines the frequency of contractions. It calculates an index that is proportional to preterm labor by integrating the area under the pressure-time curve. Furthermore, it enables the doctor to view the frequency spectrum of intra-uterine contractions. This information will help the FTC team to determine and quantify the onset of preterm labor more accurately, which is essential for effective treatment.

Benefits

Endoscopic surgical approaches, as performed by the FTC at UCSF, require small pill-sized transmitters with outside diameters less than 10mm and lifetimes over several months in order to monitor the fetus after surgery and to detect preterm labor. The pill-shape and small size of the transmitter, its ultra-low power consumption and long lifetime, and the powerful capabilities of the data analysis software make this system unique. The developed system is a substantial advancement in the art since it allows the pediatric surgeon for the first time to monitor intra-uterine pressure changes in real time and to get immediate information on contraction frequency and intensity. This information is essential for detecting and treating preterm labor, a serious problem that occurs in all fetal surgery patients. The portability of the system makes it easily adaptable to any hospital setting and ideal for use in a home-based monitoring environment. The innovation opens a new field of applications in fetal monitoring.

Potential Commercial Uses

The pressure/temperature pill is the first of a family of pill transmitters that will measure a variety of physilogical parameters. Subcutaneous pH-monitoring of the fetus, for instance, is of great importance in fetal surgery. A pH/temperature pill, similar in design to the pressure/temperature pill, is currently being developed by S2K! A pill transmitter that measures pressure, temperature, and pH has already been designed. Another parameter of interest is the heart rate of the fetus. An ASIC (Application Specific Integrated Circuit) will be developed to incorporate four physiological parameters- pressure, temperature, pH and heart rate - into one pill transmitter.

The applications of these new pill transmitters are numerous and go beyond fetal surgery. Since they are small enough to be swallowed, the pills can easily provide information on stomach-acid, for instance, without the need for surgery. Intestinal pressure changes could be monitored as well. Future pill versions could measure ECG, blood gas (O2, CO2), and blood glucose, as well as ions like potassium, calcium, and sodium.

Technology Commercialization Status

This technology opportunity is part of the NASA Technology Commercialization Program. The program seeks to stimulate development of non-aerospace commercial applications from NASA developed technology. NASA Ames Research Center is currently seeking partnerships to develop commercial applications for the Implantable Biotelemetry System for Preterm Labor and Fetal Monitoring.

Licensing options are available.

Contact

For more information, please contact the Ames Commercial Technology Office Technology Commercialization Manager at:

email: dlackner@mail.arc.nasa.gov
Phone: (650) 604-5761