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Core Temperature Measurement Goes High Tech

Pill Sensor Enables Wireless Monitoring

Recent, high-profile heat illness deaths in professional sports have heightened interest in technological tools that can prevent future fatalities. A pill sensor that can wirelessly transmit a patient's core body temperature, used for years in research laboratories and in the space program, is now poised for use on the sidelines and at other activity events.

The swallowable sensor of the CorTemp monitoring system (figure 1) contains a temperature-sensitive quartz crystal oscillator and a silver oxide battery. The pill (figure 2), encased in epoxy and covered with food-grade silicon, transmits a continuous, low-frequency radio signal that varies with body temperature. The information is transmitted by near-field magnetic link to a handheld recorder.

From Space to Sports Medicine

Susan Y. Smith, product manager for HQ Inc, the Palmetto, Florida, company that manufactures and distributes CorTemp, says the technology for core temperature telemetry is not new. HQ Inc acquired the patent and licensing rights from the National Aeronautics and Space Administration (NASA) to market the pill in the mid 1980s. "Prior to CorTemp, there was a German-made pill called the 'Heidelberg capsule,' which was on the market for 30-plus years," she says. Core temperature telemetry has been traditionally used in research studies, Smith says, including detecting hypothermic and hyperthermic conditions in astronauts during space flight. Other examples of research applications have included tracking circadian rhythm over phases of the menstrual cycle,1 recording the core temperatures of search and rescue divers during extreme conditions,2 and determining core body temperature in patients who have chronic fatigue syndrome.3

What's new, she says, is the technology's spread to sports settings, a trend that she links to growing concern about heat illness in athletes. Because wireless temperature monitoring is costly, Smith predicts that CorTemp won't be used to track large numbers athletes in mass sporting events; the disposable sensor pills cost about $40 apiece, and the handheld monitor costs about $2,500. Wireless temperature monitoring is most likely to be used during activities that involve great heat exposure, she says, such as football, tennis, auto racing, endurance events, and occupational activities such as firefighting.

Smith acknowledges that rectal temperature measurement is the gold standard in gauging core body temperature in the sports setting. The ingestible sensor is unique, she says, because it allows researchers and clinicians to gauge core body temperatures in the field.

The ingestible temperature measurement system has been scientifically validated during rest and activity in ambient and hot conditions4,5 as well as in cold conditions.6 The accuracy has been found to be within 0.1°C of other core temperature methods.

The System in Action

CorTemp is a medical device, and purchase of the system requires a physician's order. The sensor pill must be taken about 2 hours before exercise. Ideally, the pill should be in the small or large intestine during monitoring. The length of time that the pill spends in the gastrointestinal (GI) tract varies by motility rate. "The average rate of 'passage' is 20 to 36 hours," Smith says.

Healthcare professionals have several options and configurations for tracking athletes. The simplest is direct manual monitoring, whereby the physician or athletic trainer holds the handset near the small of the athlete's back. "With one quick click, the core temperature displays on the LED on the recorder. In theory, you can take the temps of 5 players within 30 seconds," Smith says. The pills are numerically coded, and each handheld unit can simultaneously monitor up to 99 athletes.

Other system components can be added to gather additional data. A strap-on heart monitor and radiotransmitter allow continuous monitoring of both heart rate and core temperature during activity. Information can be transmitted to a personal digital assistant (PDA) and/or personal computer, and an alarm can be set to sound when an athlete's temperature reaches a certain cut-off point. Data can also be downloaded from the handheld unit to a computer for analysis after the event.

According to literature from the company, CorTemp may not be appropriate for patients who have swallowing disorders or those undergoing abdominal surgery. The device may not be effective for monitoring the core body temperatures of obese patients because the sensor has a radial range of about 24 in. from the handheld unit (or the transmitter antenna).

Contraindications include patients who:

  • Weigh less than 80 lb,
  • Have a known or suspected obstructive disease of the GI tract,
  • Exhibit or have a history of exhibiting gag reflex impairment,
  • Have undergone GI surgery,
  • Have felinization of the esophagus,
  • Might undergo magnetic resonance imaging while the sensor is still in the body,
  • Have a hypomotility disorder of the GI tract, or
  • Have a cardiac pacemaker or other implanted electromedical device.

Reaction Among Health Professionals

CPT Chad Asplund, MD, a family practice physician in the department of family practice at Dewitt Army Community Hospital in Fort Belvoir, Virginia, has frequently encountered patients who have heat-related injuries in his work with soldiers in basic training and runners in marathons. He says that CorTemp would be more applicable to basic training, because participants are able to stop and be monitored. "In marathons, it would be more difficult, because most runners will run until the finish," Asplund says. He says he's intrigued by CorTemp's potential to answer several unanswered questions that healthcare professionals have about heat illness. "There hasn't been a lot of good research on core temperature and manifestation of heat injuries," he says, noting that some people "fall out" with a core temperature of 104°F, while some can continue participation with a core temperature of 106°F.

William O. Roberts, MD, a family physician in St Paul and president of the American College of Sports Medicine, agrees that CorTemp's greatest benefit will be in field research, from hot, humid football camp to cold-water swimming. Roberts, who is medical director of the Twin Cities Marathon, says he doubts that the system could be widely used in a mass participation event such as a marathon. "The cost is high, and it only works if it stays in, which is a problem with some runners who have active GI tracts," he says.

Douglas J. Casa, PhD, ATC, director of athletic training education at the University of Connecticut in Storrs, used CorTemp on the football sidelines. He and his staff used CorTemp in August 2003 to evaluate the National Collegiate Athletic Association's new heat illness prevention model. They monitored 15 players for the first 8 days of football practice. He believes that CorTemp will be clinically useful for monitoring at-risk individuals, such as those who are not acclimatized, have a high percentage of body fat, or have a history of heat illness. He points out that rectal temperature measurement is still needed to diagnose heat illness.

Athletic trainers were able to easily measure players' temperatures during the normal flow of football practice. He says that the linemen typically had core temperatures that were greater than 102°F, and some were greater than 104°F, despite the fact that the staff aggressively pushed fluids. All of the players tolerated the pill, and none had any heat-related symptoms. "The reassurance seemed amazing. It's not a matter of wondering or having to wait for a player to have symptoms," Casa says.

Wireless core temperature monitoring will enable medical professionals to learn things about athletes that can't be studied in the lab, says Casa, who has worked with HQ Inc on some research studies. "In the long run, we can't prevent all heat illness incidents, but we can do more than we're doing now," he says.

Lisa Schnirring


  1. Coyne MD, Kesick CM, Doherty TJ, et al: Circadian rhythm changes in core temperature over the menstrual cycle: method for noninvasive monitoring. Am J Physiol Regul Integrative Comp Physiol 2000;279(4):R1316-R1320
  2. White LJ, Jackson F, McMullen MJ, et al: Continuous core temperature monitoring of search and rescue divers during extreme conditions. Prehosp Emerg Care 1998;2(4):280-284
  3. Hamilos DL, Nutter D, Gershtenson J, et al: Core body temperature is normal in chronic fatigue syndrome. Biol Psychiatry 1998;43(4):293-302
  4. Kolka MA, Quigley MD, Blanchard LA, et al: Validation of a temperature telemetry system during moderate and strenuous exercise. J Therm Biol 1993;18:203-210
  5. Sparling PB, Snow TK, Millard-Stafford MD: Monitoring core temperature during exercise: ingestible sensor vs. rectal thermistor. Aviat Space Environ Med 1993;64(8):760-763
  6. O'Brien C, Hoyt RW, Buller MJ, et al: Telemetry pill measurement of core temperature in humans during active heating and cooling. Med Sci Sports Exerc 1998;30(3):468-472

Field Notes

Breathing Easier in the Pool

Pool maintenance engineers—including backyard pool owners—and swimmers who enjoy the benefits of pool exercise should be aware of the potential hazards of heavy chlorination. Trained swimmers face a higher risk for exercise-induced bronchoconstriction (EIB) if they swim in heavily chlorinated water, according to a study presented at the annual meeting of the American College of Sports Medicine in June in Indianapolis. The risk was the same for swimmers who had a history of EIB.

The exercise tests were performed in swimming pools with chlorine concentrations of 0.0 ppm, 0.5 ppm, 1.0 ppm, and running or cycling next to one of the pools. A calibrated hand-held spirometer was used to measure the lung capacity of swimmers who completed four different exercise tests of the same intensity and duration. A fall in forced expiratory volume (FEV1) of 10% or more was considered positive. At 0.5 ppm, the incidence rate for EIB was just under 20%, the same as for exercise outside the pool. When chlorine concentrations reached 1.0 ppm, the rate of EIB jumped to 60%.

"We've long suspected that chlorine has an adverse effect on the respiratory health of swimmers. Now we know the likelihood increases significantly with the concentration of chlorine used," said Arthur J. Williams, MD, of the Sport Science Institute of South Africa in Cape Town. "We believe these hazards can be minimized through awareness and proper pool maintenance," he added. Physicians who prescribe pool exercise, especially for patients who have asthma, should advise them to seek out pools where the chlorine level is kept below 0.5 ppm.

Patricia D. Mees

Lighter Baseballs and Youth Injuries

Overuse injuries are a concern among youth baseball players partly because they use the same size and weight ball as major league players. A new study reveals that young players who use a baseball just 1 oz (28.4 g) lighter than the standard ball maintain proper mechanics but throw with significantly more velocity. Researchers presented their study at the annual meeting of the American College of Sports Medicine in June in Indianapolis.

The investigators tested 34 young pitchers (age range, 9 to 12) in a biomechanics laboratory. Pitchers threw 10 pitches with a 4- and a 5-oz baseball. Their pitching results were videotaped and analyzed for pitching biomechanics (especially elbow and shoulder motion) and ball velocity. Pitchers who used the 4-oz ball had no significant difference in pitching motion but had increased velocity. Such findings have both health and game implications. "It stands to reason that if a young pitcher, whose bones and joints are still growing, can perform better using a lighter baseball, then it would be better for the pitcher as well as for the game of baseball," said Shawn Drake, PhD, one of the study authors. Investigators suggest that in light of these findings, youth baseball organizations should begin to try using the lighter baseballs in games and practices.

Paul W. Mamula, PhD

Dehydration Risk During Summer Youth Sports Camps

Children participating in summer sports camps may not be adequately hydrated, even if water and sports drinks are accessible and coaches urge drink breaks during activity. More than two thirds of young soccer players are dehydrated on or during activity, according to research results presented at the annual meeting of the American College of Sports Medicine in June in Indianapolis.

The investigators tested 34 boys (average age, 13) and 24 girls (average age, 12) who participated in 4-day soccer camps in Pennsylvania during July 2003. Camp activity consisted of three, 2-hr sessions for boys and three, 1.5-hr sessions per day for girls. Camps had stocked coolers within 25 m of all sessions, frequent rest breaks, and coaches who encouraged players to drink during breaks or at any time during practice. Investigators measured urine specific gravity before the first practice of the day and after the second session of the day.

Most of the players were dehydrated by the second day of camp; more than half of the girls were seriously dehydrated at this point. By the last day of camp, 59% of boys and 70% of girls were significantly dehydrated. Douglas J. Casa, PhD, ATC, director of athletic training education at the University of Connecticut in Storrs said, "It is a real safety issue when the majority of kids are beginning intense exercise in the heat already dehydrated." The researchers cite these results as especially worrisome, because the conditions during the study were mild for the summer and hydration strategies had been implemented. They do emphasize, however, that hydration problems are avoidable with proper fluid replacement strategies and education.

Paul W. Mamula, PhD