Architecture

The evolution of low-power wireless communication technologies like Zigbee (IEEE 802.15.4), low-power Bluetooth^*, etc. has enabled the development of small, body-wearable, wireless sensors for patient monitoring.

As shown in Figure 2, these sensors can be configured to form a Wireless Body Area Network (WBAN) [3] and enable monitoring of multiple bio-parameters (such as ECG, Pulse Oxygen saturation, Blood Pressure, etc.) of multiple patients at a central location. Each body-wearable sensor, known as a Bio-Front End device (BFE), is composed of a sensor for bio-signal sensing, the related front-end hardware, a low-power microcontroller for data acquisition and a wireless transceiver for data transfer to the receiver. There can be multiple BFE devices connected to a patient for monitoring multiple parameters. An aggregator (AGG) device worn by the patient performs the function of receiving the wirelessly transmitted data from multiple BFE devices connected to a patient and transmits the aggregated data to a backend PC or server. The AGG device can be a device like a Portable Digital Assistant (PDA) or a scaled down version of that without a Liquid Crystal Display (LCD). The AGG and the BFE devices form a localized WBAN, with each BFE device having a unique device ID.

Figure 2: Architecture of a body-wearable, wireless health monitoring platform
click image for larger view
 

Following are the advantages of this architectural framework:

• The functional partitioning of the PMS allows a single PC to cater to the computing and results display requirements of multiple patients, thereby reducing the cost of the overall system.
• There is better resource utilization since a single resource (like a network printer) can be shared across multiple patients.
• It enables patient mobility and comfort.
• It allows central monitoring of multiple patients from a single location.
• It allows the entire patient-monitoring framework (consisting of WBANs of multiple patients) to be managed from a central location.
• Such a framework does not require the doctor to be in close proximity to the patient or to the monitoring equipment, since the patient's physiological data can be made available to the doctor anytime and anywhere on his hand-held communication device.

System components in the health monitoring framework

There are three major components in the health monitoring framework as shown in Figure 3:

• The BFE device.
• The AGG.
• The backend computational platform such as a PC or server.

Figure 3: System components of a self-managing framework for health monitoring
click image for larger view
 

The Bio-Front End

The BFE device, which is worn by the patient, consists of the sensor, the front-end hardware and firmware for processing the sensor signals, a low-power microcontroller and a low-power wireless transceiver device for communication. The communication technology between the BFE and the AGG device can be based on a low-power wireless standard like the 802.15.4 (Zigbee) or low-power Bluetooth in order to maximize the battery life. The type of sensor and the front-end hardware is specific to the physiological signal being measured. For example, if the BFE device is designed to monitor ECG, the sensors would be pre-gelled electrodes, whereas for pulse oximetry, the sensor would be an optical finger probe. The microcontroller controls the overall functionality of the device and performs the functions such as data acquisition, device control, data formatting, packet forming, wireless transmission and execution of the commands sent by the AGG device.

The Aggregator

The AGG device is also worn by the patient and it serves to aggregate the data from multiple BFE devices connected to a patient and sends these data wirelessly to a PC for further processing. The AGG uses low-power wireless technology like Zigbee to communicate with the BFE devices and Wi-Fi or other appropriate communication technology to communicate with the PC, since the required data rate and range is larger than that for a body-area network. The AGG device also serves as the intermediate messaging link between the BFE device and the PC.

The Personal Computer or server

The PC is used to collect data from multiple AGG devices connected to multiple patients and process these data. The PC also serves to display the physiological waveforms and parameters of several patients on the screen, does further signal processing and computation, performs feature extraction, stores data, and communicates with other terminals over the Internet protocol. The PC also keeps the doctor updated on the patient status by sending the patient information on his mobile phone or PDA. It also manages resources such as printers, scanners, and other devices, which are shared across multiple patients.