Patent Application
20160262620
This disclosure relates generally to patient monitoring. Particularly to ECG monitoring.
When a patient is being monitored by ECG it is greatly desirable to do it wirelessly, as nurses have problems with tangled cables, and patients need to be mobile.
Multiple ways for managing ECG and telemetry cabling are available and have been proposed as described in [1]. Telemetry also has problems, e.g. battery life, battery change, battery charging, pairing of the patient worn transmitter with the receiver/display after each disconnect (typical after battery change or charging). Pairing is a specific problem in wireless monitoring, as it has to be clear which patient connects to which ECG waveform (and other display, alarms etc.); a problem not encountered with wired monitoring. Other issues with telemetric monitoring is its limited compatibility with wired monitoring, especially with patient occasionally mobile, e.g. toilet visits. The switching between devices is cumbersome and error prone.
The present invention is a novel approach in combining wired and wireless ECG monitoring. Here an ECG Wireless Plug (“Wplug”) is inserted between the Trunk Cable and the Leadwire Cable, so as to both pass the ECG to the Host Monitor, and to intercept the signal for processing and wireless transmission.
One preferred embodiment of this is a Wplug that has two connectors on opposite sides, one Trunk connector intended to mate with the Leadwires and one Leadwire connector intended to mate with the Trunk Cable. The Wplug has its own battery to feed the electronic part that intercepts the ECG on its way to the Host Monitor, processes it and sends it wirelessly to a Wireless Host, e.g. a Smartphone, a Central Station or the Host Monitor wireless receiver. This “Basic” embodiment has the advantage of not requiring modifications to the Host Monitor, but has limited functionality and must have its own battery replacement or recharging arrangements.
Another preferred embodiment is a version can charge the battery from the Host Monitor, but requires modification of either the Host Monitor or the Trunk Cable.
Still another preferred embodiment uses digital communication, e.g. USB, with the host.
Both the charging and the USB communication can be embedded in the redundant shield pins in a typical Leadwire and Trunk Cable connectors.
All versions can also support identifying the patient on the Wireless device (Pairing) by, at least briefly, have both the Host Monitor and the Wplug capture the ECG. The Wireless Host then compares the, initially unpaired, ECG waveform stream from the Wplug with a set of candidate ECG waveforms streams of Named Patients (normally the patients of the supported hospital department). Correlating the waveforms or physiological parameters derived from the waveforms (R-R intervals, Heart Rate . . . ) produces a Pairing with virtually 100% reliability.
Still another preferred embodiment uses the Wplug Host Monitor side connector (the “L” connector) to allow connection to an expanded set of Leadwires C2 . . . C6, also known as the Chest Leads or Precordial Leads in a 12 Lead ECG. As implemented in
Having the processing close to the patient is advantageous, as the effects of communication disturbances are minimized.
The detailed design of “eavesdropping” on the signals from the patient to the host is crucial. The Wplug must show high impedance in all eavesdropping connections so as not to reduce ECG performance of the Host Monitor. Note that the Host Monitor typically has defibrillation protection resistors in its front end, which means that during defibrillation the voltage between any leads can rise to 5000 volts. Also, the Host Monitor may use Impedance Respiration, meaning it feeds 30-100 kHz current to the patient and measures chest impedance variations. None of this can be disturbed by the Wplug.
Special attention must be given to the Right Leg Drive (RLD), a standard way of reducing noise in an ECG monitor, as it involves active feedback from the ECG amplifier system into the patient. The Wplug RLD must be very weak or switchable to off when the Host is connected. Host connection can be detected by the Wplug in various ways: by using the standard Leads Off mechanism, where a small current is injected into the electrodes to measure DC or AC impedance, or by detecting the presence of the shield connections (Rash, Lash . . . ) which the host connects to floating ground. Fortunately the need for RLD in wireless mode is much smaller than in standard Host Monitor mode, as the leakage current through the Host Monitor ECG floating front end is essentially missing. The preferred design is weak RLD by using a large value for the defibrillation resistor Rdef.
Also the Leads Off mechanism should be flexible and adapt to the Host Monitor Leads Off mechanism when connected. Otherwise the mechanisms will interfere.
The Basic design has a replaceable battery (alkaline, lithium, rechargeable) or a built in battery. In the case of a replaceable battery, it is desirable to have a super capacitor as internal backup, as it enables operation during the time the battery is removed from the Wplug. With good industrial design battery replacement takes less than one minute, which a 1 Farad super capacitor can easily support.
If the Wplug is replaced with a second device while the first one is removed for charging, the Pairing needs to be re-performed. The Wireless Receiver detects the break in operation, and automatically performs or requests a re-Pairing.
Small variations in the connectors are included in the invention. Examples of these are the use of 6 Lead ECG connectors instead of 5 Leads (6 Leads adds C2 to the standards 5 Lead connector. Also a unified 3-5-6-12 Lead connector can be used [2].
A 3 Lead cable can be used on the patient side, but the Host port must use at least a 5 Lead connector that has a dedicated N pin.
It is obviously much more elegant to have Host Monitor support for power. In case of a Host Monitor that is supportive of the Wplug, it is useful to add a direct wired communication modality to the Wplug, e.g. USB. This can be used for several purposes, e.g. making the pairing faster and less dependent on correlating ECG waveforms. Again, the easiest way of doing this is using the redundant “T” and “L” connector shield ground pins.
Normally this allows 12 L ECG only when in non-Host mode, but it is obvious that a multiport adapter is easy to design, which would allow all modalities to be used simultaneously.
The Wplug can also be used for other physiological monitoring, e.g. a pulse oximeter. In addition to dedicated connector for this, a Host port that is redundant when not connected to a Host Monitor, can be used to connect an oximeter or an oximeter probe.
