I've been a hypochondriac ever since I was a kid. As an eight-year-old, I was terrified of having a heart attack, and no amount of parental reassurance could erase this fear. In my childish reasoning, these worries seemed perfectly logical--heart attacks were the most common cause of death in my family, and they appeared to strike without much warning. At my most panicky moments in the middle of the night, the only way I could fall asleep was if I kept my hand pressed against my sternum to convince myself that my heart was still beating. When I confessed these anxieties to my father, he tried to point out the ridiculousness of my behavior by suggesting another method of self-diagnosis: "You should also stick a finger in your nose to see if you're still breathing."
My hypochondria has eased a bit over the past 35 years--now I worry more about my kids' health, freaking out over every sniffle and scrape. But I recently discovered that monitoring heart rate and breathing during sleep is not such a ridiculous idea after all. More than 12 million Americans suffer from sleep apnea, a disorder characterized by frequent interruptions of breathing. The cause can be either obstructive--a temporary closing of the soft tissues around the airway--or neurological; in both cases, the condition forces the sleeper to awake briefly to resume breathing, as many as 400 times in a single night. If left untreated, the disorder can raise the risk of cardiovascular problems, but the great majority of sufferers simply endure their nightly struggles and constant fatigue. One obstacle is that doctors cannot definitively diagnose sleep apnea unless the patient spends a night under observation in a sleep lab.
Now a better solution may be at hand. VivoMetrics, a company based in Ventura, Calif., has fashioned a wearable device that can record vital signs throughout the day and night. Called the LifeShirt, it is a sleeveless spandex garment equipped with an electrocardiogram (ECG) for gauging heart rate and embedded wires for measuring respiration. In Denver, a clinic run by Kaiser Permanente is using the LifeShirt to monitor sleep problems in children. "The sleep lab can be a miserable experience for kids," says Elizabeth Gravatte, director of marketing for VivoMetrics. "But they love the LifeShirt. They even brag about wearing it." By examining the data collected by the device, physicians can determine whether a child has sleep apnea and whether the condition is serious enough to warrant a surgical intervention, such as the removal of the tonsils or adenoids.
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The LifeShirt has already proved useful as a tool for medical research. Since the U.S. Food and Drug Administration approved the device in 2002, it has been employed as an ambulatory patient monitor in a variety of studies, ranging from an investigation of coughing in patients with chronic lung diseases to an assessment of stress in subjects with autism. The main advantage of the device is that it can provide researchers with a continuous stream of information about a patient's health. Instead of relying on intermittent tests conducted during office visits, physicians can analyze heart and respiratory rates measured over long periods and use the system's software to pinpoint signs of illness among the reams of data. Given my lifelong interest in my own vital signs, I was quite intrigued by the LifeShirt. I invited the people from VivoMetrics to come to my office, giving them my chest and abdomen measurements so they could bring along a device that would fit me.
I have to admit, I was a little embarrassed as I donned the LifeShirt in the men's room, pasting the electrodes of the ECG to my chest and squeezing myself into the tight-fitting black spandex. When I emerged, Alex Derchak, director of clinical development for VivoMetrics, explained why the LifeShirt has to fit snugly: the device measures changes in the volume of the rib cage and abdomen by analyzing the frequency of weak oscillating currents flowing through wires embedded in the shirt's elastic bands. A phenomenon called self-induction is at work here: as the current oscillates, the magnetic field around the wire changes, too, inducing voltages that slow the oscillation. The degree of self-induction is proportional to the cross-sectional area of the circuit. As the wearer of the LifeShirt breathes in, the circuit expands and self-induction rises, lowering the frequency of the oscillating current; as the wearer breathes out, the opposite happens. [break]
Derchak connected my LifeShirt to a handheld unit that stores the recorded data on a compact flash memory card. The unit has a touch screen that allows patients to report their symptoms, moods and activities while wearing the LifeShirt. The requested information can vary depending on the type of clinical study. (During sleep studies, the handheld gadget is usually tucked inside a pillow.) The LifeShirt also comes with an accelerometer that can track the wearer's posture and activity level, indicating whether he or she is lying down or standing up, walking or running.
To demonstrate the device's abilities, Derchak suggested that I take a jog down the hallways of the Scientific American headquarters. Feeling incredibly foolish, I did three laps through the corridors while my colleagues gaped at me from their offices. "Don't be alarmed!" I called out. "It's all for science!" Derchak gave me a minute to catch my breath and then instructed me to lie down on the floor. (Luckily, he didn't order me to do any push-ups.) After a few more minutes, Derchak popped the flash card out of the handheld unit and inserted it into his laptop so we could review my results.
The laptop's screen displayed an array of squiggly lines. The top line showed my tidal volume--the amount of air inhaled with each breath--over the 16 minutes that I'd worn the LifeShirt. The middle lines detailed my raw ECG data and heart rate, and the bottom lines delineated the jolts of my physical movements. The software allowed us to focus on specific intervals of the LifeShirt session: when I was talking, when I was running, when I was lying down. I was fascinated to see how my breathing changed when I was speaking--each squiggle elongated as I took a big gulp of air and let it stream out over several seconds. When I was jogging, my heart rate climbed from 93 to 127 beats per minute, and the number of breaths per minute jumped from 19 to 38. And although I was exercising for only a minute and a half, it took more than two minutes for my heart rate to settle back to normal.
The LifeShirt can be outfitted with additional monitoring equipment, including a pulse oximeter for measuring the amount of oxygen in the blood and a throat microphone for determining the frequency of coughing. What is more, VivoMetrics is evaluating other uses for the high-tech garment besides medical research. Fire departments in Connecticut and Minnesota have tested LifeShirts in training exercises; worn under the firefighters' flame-retardant suits, the devices can wirelessly transmit data on heart rate, breathing, blood oxygen level and body temperature to officers in a nearby command truck. And the U.S. Army has signed a contract with VivoMetrics to incorporate the company's technology into a system designed to monitor the vital signs of soldiers during battle.
But you can't buy your own LifeShirt just yet. VivoMetrics currently leases the garments to clinics and research groups; although the company may eventually offer the LifeShirt to consumers, the plans for retail sales and pricing are still vague. Considering the number of hypochondriacs out there, that's probably just as well.