William Hyman: Closed-Loop Control and Patient Equipment

I have addressed closed-loop medical devices twice in this blog space: first, with respect to a sedation delivery system and second, with respect to insulin delivery. In both cases, there is a drug delivery device that monitors appropriate patient variables and adjusts the dosage accordingly.

At a recent meeting of the New York Metropolitan Area Clinical Engineering Directors Group, I learned about the LifeVest technology from Zoll. (I have no professional association with Zoll and I am not endorsing this product.) The LifeVest is an externally worn defibrillator-in-a-vest with an attached electronics package. The device monitors the patient’s ECG and when appropriate initiates a sequence of events leading to a defibrillating shock—without the need for human intervention. A device operator is not required. However, if the vest wearer is still conscious and alert, he or she can interrupt the sense-evaluate-deliver sequence with manual buttons. A nice piece of supporting technology is that the built-in “paddles” are dry until just before a shock, when a signal causes release of a blue gel. Besides facilitating defibrillation, the blue material is also an indicator that a shock sequence has occurred. With training, EMS and ED personnel will recognize both the vest and the blue indicator. This system is truly closed loop, unlike AEDs which require an operator to initiate use and to manually trigger the shock. The key closed-loop questions apply here. Will the device respond properly when it should and not respond (shock) when it shouldn’t? A premarket clinical trial and ongoing performance monitoring are said to suggest that the answer is predominantly yes.

The LifeVest might trigger the classic question of what to do about patients using their own (or, in this case, rented) medical equipment in the hospital, either for patients that come in because they have been resuscitated by the device or for another reason. In the case described above, there would need to be some re-upping of the device’s capability. While one might argue that patients in a hospital do not need their defibrillators, at least some patients would insist on using their own device, especially if they believed it had just saved their life. Moreover, it would make for an interesting discussion if a patient was denied the use of his or her own defibrillator, and then had a cardiac event that was not adequately responded to by the hospital staff.

As a result of this presentation, I was reminded that ICDs are also closed loop, i.e., they too sense and respond without any human intervention. Pacemakers (or artificial pacemakers to be more exact) also have a degree of automatic physiologic responsiveness. An interesting technology in the latter is the use of an accelerometer to detect increased patient activity and then predict the need for more cardiac activity. This is cleverly indirect.

Closed-loop control offers the possibility of improved patient opportunities and outcomes. In this regard, the notion of medical devices “talking to” and controlling each other has often been raised in interoperability discussions—although what they are talking about and who created the script is often a bit vague. Nonetheless, it can be expected that more closed-loop products, or systems, will be entering the market, preferably subject to reasonable proof of safety and efficacy.

William Hyman, ScD, is professor emeritus of biomedical engineering at Texas A&M University. He now lives in New York where he is adjunct professor of biomedical engineering at The Cooper Union. Hyman may be contacted at w-hyman@tamu.edu

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