Contributed editorial appearing in
Scientific Computing & Instrumentation 18:3, February 2001, pg. 14.
Ask an American in their early fifties to name influential people and events of the 1960s and odds are good the list will contain John, Paul, George, Ringo, and the Vietnam War. Pose the same question to an early thirty-something and you are likely to hear Captain James T. Kirk, Mr. Spock, Dr. Leonard McCoy, and the Apollo 11 moon landing. Non-technical commentators will often observe that a new development “came out of nowhere” and wonder “who would have expected it.” Well, Gene Roddenberry and his gifted staff of Star Trek script writers for starters. Critics rolled their eyes when their characters stored reams of documents on a thin, square, memory cartridge, or talked to the ship using hand-held communicators. I have to chuckle when I toss a handful of Iomega Zip disks into my briefcase and grab my cell phone before heading off to the office.All of my students in instrumental analytical chemistry know that as soon as we develop a hand-held “tricorder” for the nondestructive analysis of all matter, I will be out of a job. The “medical” tricorder used by Starfleet was a specialized analysis device able to record vital signs and even sequence DNA by simply waving a detachable sensor probe over the organism. Such a device would have been useful during the 2000 presidential election. On the morning of Wednesday, November 22, then vice presidential candidate Richard B. Cheney awoke with chest pains and was admitted to the George Washington University Medical Center. An electrocardiogram (ECG) and early cardiac enzyme analysis did not indicate problems, but further tests later in the day revealed he had suffered a “very slight” heart attack. Had the ECG been captured and analyzed during or immediately after the attack, perhaps the correct diagnosis would have been apparent sooner.
lnstromedix manufactures personal cardiac event recorders to aid in the diagnosis of irregular heartbeats and arrhythmia. This credit card sized “HeartCard” is carried by the patient and placed on the chest during an episode. The HeartCard stores a 30-second ECG that can be transmitted to the physician over the handset of any telephone. An available pager-sized model can continuously record a 5-minute ECG loop. The technology involved with the acquisition and transmission of such biophysical data is known as “biotelemetry.”
Implantable “biotelemeters” permit the acquisition of physiological parameters measured inside the organism. The Fetal Treatment Center (FTC) at UC San Francisco along with Sensors2000! at NASA Ames Research Center has developed miniature biotelemeters for pre-term labor and fetal monitoring. The FTC develops minimally invasive endoscopic techniques used for fetal surgery and required a device to detect the onset of postoperative pre-term labor. The pill-sized transmitter measures body temperature and intrauterine pressure using a thermistor and a piezoresistive pressure transducer. These solid-state components are encapsulated in biocompatible silicone rubber along with a 22 x 8 mm printed circuit board and batteries that permit 10 months of continuous operation. The measurements are transmitted on a carrier frequency in the range of 174 to 216 MHz and are encoded using pulse interval modulation (PIM). A pair of pulses is transmitted every 500 to 1000 milliseconds and the time interval between successive pulse pairs is proportional to the measured temperature while the interval between the pulses of each pair is proportional to pressure. The receiver is placed 3 to 10 feet from the patient and is attached to a traditional data acquisition and analysis system running application software written in National Instruments LabVIEW. NASA is maturing the technology to include measurements of pressure, temperature, pH, heart rate, ECG, blood gas, blood glucose, and electrolyte concentration for studies to be conducted on the International Space Station.
The Biomechanics Laboratory at the Free University of Berlin uses biotelemetry to study the forces and performance of orthopedic implants comprised of varied material and of differing design. They have placed 8-channel PIM-encoded transmitters in artificial hip joints, spinal fixators, shoulder joints, and replacement spinal vertebrae. The biotelemetric hip joint is instrumented with strain sensors and a thermistor. The magnitude and direction of joint forces on the implant and its temperature can be measured in vivo at a rate of 200 Hz. This valuable data, that previously was only attainable through mathematical modeling, is used to improve the durability and performance of future implants. To eliminate the requirement of massive batteries and the inconvenience of an external power supply, a 45 Vpp coil operating at 4 kHz inductively powers these biotelemeters. The hip joint uses a ring coil placed around the leg while a flat coil placed on the patient’s back inductively powers the spinal fixators.
Similarly, Carolina’s Medical Center Biotelemetry Project is developing biotelemeters for standard fracture fixation plates, intramedullary rods, and total joint systems. These ‘smart implants” would be monitored for performance and condition during routine office visits in the same fashion that auto mechanics are able to run a diagnostic on electronic fuel injection systems. Before the broadcast news anchors issue the hackneyed “What will they think of next,” perhaps they should watch a few episodes of the Six-Million Dollar Man.
