Sensor Networks for E-Health: A Survey

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Abstract

Health care –or sometimes referred to as E-health- has recently been a hot topic for researchers in computer science. The availability of new sensing technologies helps develop different types of health care applications and raised the concept of e-medicine as well. This paper surveys the state of the art of health care sensing technologies, devices, and applications. In addition, the use of expert systems in health care is presented. This includes diagnosis, suggestion for treatment, and prediction possible effects of different therapeutic interventions.

Keywords

Heath care, E-health, E-medicine, sensor network, health management, patient monitoring.

  1. Introduction

Health care is an essential topic that includes many issues. Some of these issues are related to the patient health and his/her protection, others are related to the patient information, and some others are associated to the used technology. In fact, these issues cannot be totally separated. Patient health is the responsibility of the hospital staff that theymight depend on smart software and hardware for diagnosis as well as monitoring the patient’s health;Artificial Intelligence (AI) and expert systems play major roles in such cases which is included as a core of many of the health care applications. At the same time, patient information is kept secure on a computer at the hospital. Staffs are the only persons that can access such information.

As can be seen from the previous scenario, there are many restrictions on such approach of handling patients’ information. For instance, if a patient in a critical health condition is admitted to another hospital that does not have his/her health record;such information might cost the patient his/her life. Nowadays, the advances of the sensing technology and networking lead to a revolution in the health care application. Electronic health (E-health) is named after the technology took place in the health applications. Patients are not required to stay at hospitals for continuous monitoring any more. They can stay at their comfort zones and their status is continuously reported to the hospitals where staff can see such information. Small but smart sensing devices such as pressure sensors play a critical rule in such case.

Throughout this paper, we give the reader the state of the art in the e-health technology and applications. Up to our knowledge, this is the first work that surveys the sensing technology along with e-health applications. We think that this survey will be beneficial to all of the researchers that are working on sensors, sensor networks, and e-health. It is the also, the first step towards deep investigation in e-health solutions.

The paper is organized as follows: Health Care Medical and Sensing Technology are investigated in the next section. Section 3 looks at some of the current sensors prototypes as well as commercial sensors that are used in the field of e-health. Section 4 presents the up-to-date e-health applications; some of these applications are very simple; others are very complicated in terms in sensing and networking. The current E-Health expert systems are categorized for the benefit of the reader in section 5. Finally, the paper concludes in section 6.

  1. Health Care Medical and Sensing Technology

Sensing technology has come a long way. Many devices have been produced in the last few years due to the high demands on such technologies as well as their applications. For instance, there are many new sensors for location identification, e.g. GSM cell and Wi-Fi, proximity, e.g. RFID tags, movement, e.g. movement sensors, and health sensors, e.g. basic vital signs and glucose. A sensor is used to measure the physical environment such as temperature, pressure, glucose level, heart rate,…..etc. The signal measured by the sensor is transferred to the processing unit via I/O ports. After processing, and recording these signals, they can be sent to a remote server. Some devices can display this information to the patient via LCD displays.

In this section, we provide the reader with the state of the art sensing technology and sensors in the field of e-health including the commercial sensors. Such survey is intended to provide the functionalities of each sensing device as well as its applicability in fitting a real life sensor networks.

2.1.Sensors Architecture

Sensors are usually consists of four main units in addition to the two optional units which are mobility support and location finding units. The four main units are, as shown in Figure xxx, sensing, processing, communication, and power units.

Figure xx: Sensors Units

Sensing Unit

A sensor is used to convert a physical parameter into electrical signal. Most of these signals are analog and week signals. Therefore, the main components of the sensing unit are the sensors which differ from application to another. The second component is the analog to digital (ADC) converter. Depending on the application a variety of sensors are available. These sensors include but not limited to[2]:

•an ECG (electrocardiogram) sensor for monitoring heart activity

•an EMG (electromyography) sensor for monitoring muscle activity

•an EEG (electroencephalography) sensor for monitoring brain electrical activity

•a blood pressure sensor

•a tilt sensor for monitoring trunk position

•a breathing sensor for monitoring respiration

•movement sensors used to estimate user's activity

•a "smart sock" sensor or a sensor equipped shoe insole used to delineate phases of individual steps

A common requirement for these sensors is that they must be small and light. Most of sensors are passive elements which indicate no need for power. However in the case of the need of power another restriction is added to these sensors. The power consumption of these sensors must be as small as possible.

Processing Unit

The processing unit is considered as the main core for sensor device. Its function is to process data and control all other modules. From many processing devices such as microprocessors, microcontrollers, DSPs, and FPGA, microcontrollers (MCUs) are considered the most common devices used in health care sensors. Microcontrollers represent the integration of many functions in a single small,cheap, and low power chip. In addition, the producing of specific microcontrollers for health care applications makes them more suitable for this task. Microcontrollers used in health care are ultra low power devices which lengthen battery life. They contain some special peripherals in addition to the normal peripherals contained in normal microcontrollers. A precise ADC ( analog to digital converter) is an important component which receive the sensor signal. LCD driver can be used to drive LCD display to show information and measurements. DACs , timers , and counters are normal components contained in most microcontrollers. Also integrated flash and RAM memory are important to store data and programs. Interfaces such as I2C, and SPI are used to easily connect microcontrollers to other components. Wireless connection can be established via RF converter contained in some health care microcontrollers.

Sensors storage as a part of the processing unit is usually built in flash and RAM memories. However in many cases they are not enough for storing programs and data. External memories are needed in these cases to compensate small memory capacities. Between many memory technologies, flash memory is considered as an optimum selection for health care sensor devices. flash is light, compact, energy-efficient, and ever less expensive. There are two kinds of flash namely : linear flash and ATA flash. Linear flash, as the name implies, is laid out and addressed linearly, in blocks. The same address always maps to the same physical block of memory, and the chips and modules contain only memory plus address decoding and buffer circuits. This makes them simple, cheap, and energy-efficient. Linear flash is the obvious choice for nonvolatile memory that's built permanently into an embedded system. ATA flash memory appears as if it was sectors on a hard disk and is accessed via the same register interface used by the original IBM PC/AT's hard disk controller (and, more recently, IDE disk drives).

The main advantages of ATA flash, from the embedded system developer's perspective, are flexibility and interchangeability with hard disks. Flash memory offerings vary widely in capacity, price, speed, and features. This makes designing with flash a non-trivial exercise; the effective embedded system designer must know the full range of available products in order to choose a cost-effective solution.One of the first tradeoffs the designer must consider-as with all embedded systems components-is the inevitable compromise between power and speed. Some flash memories can run at lower voltages (as low as 3V or less), which saves power, but works more slowly. Others run at higher speeds but require five or even 12V.

Communication Unit

Communication module is a vital component in health care sensor to send data to a server to monitor data, store information, or take an action. This server can be mobile phone,laptop,internet, or a hospital. Many technologies are available with different characteristics of power, communication distances, bandwidths, and transfer rates. Bluetooth technology has a range of 100 meters and not necessarily is in sight and the power used by Bluetooth is very less. The nearest competitor of Bluetooth is infrared. Infrared has many additional features but it loses on one point with Bluetooth, as infrared rays cannot pass through the walls and other obstacles. Infrared technology is up in rate of data, Bluetooth has 1MBps whereas infrared has 4 MBps. Infrared is faster than Bluetooth technology.Wi-Fi uses RF waves to exchange data; however Wi-Fi has a larger range than blue tooth.Communicating to a distant server such as hospitals requires another technology. GSM is the best solution for this task.

ZigBee is an attractive communication technology for our application.

Give me an example on the sensing devices that use each technology,please?

Power Unit

Many technologiesare being focused on how to operated devices with reduced power consumption, but at the same time battery technologies need to catch up with application requirements.There is certainly no shortage of battery- and chemistry-related technologies, ranging from regular lithium-ion batteries to portable rechargeable batteries to fuel cells. Portable rechargeable cell chemistries include Alkaline, Nickel Cadmium (NiCd), Nickel Metal Hydride (NiMH), and Lithium Ion (Li-ion). The Li-ion cells have the highest energy density by both weight and volume. With the appropriate level of safety designed into a Li-ion pack, Li-ion offers the most attractive method of portable battery power.

  1. Heath Monitoring Sensors

Before describing some of the sensors applications in the field of health monitoring, it is appropriate to look at the current sensing devices that are used in this field. The following are some of the commercial devices that used separately or part of an application.

Pocket PC

Smart Pocket PCs play an important role in different application. Since they are always carried by a human, it can be used to help people in many different directions. The usage of the Pocket PC in e-health could be essential in applications such as cutting smoking. One of the real example is “ My last Cigarette” project[20]; such project , as shown in Figure xxxx, displays nicotine level readout , expected cravings readout , daily motivational quote or medical fact, deaths since you quit readout , daily motivational message, and many other features. These readings are extracted through a simple nicotine patch that is connected to the pocket PC holder. It is really impressive how such device can help saving his/her holder life since the holder could be dying for data; the reader is referred to this story to realize the importance of keeping the medical information along with the patient

Pocket PC / My last Cigarette Software
Figure xxxx: Pocket PC[2]

Medical Alerts and Recording Devices

Nowadays, human accessories became important medical devices. For instance, the simple bracelets or necklaces, shown in Figure xxxx, could hold the holder person’s medical information in forms like RFID tag, barcode, or the patient ID is just engraved on the back of it. One of the real applications is the CADEX watch [21]. This watch is used to save the patient critical information such as his/her hospital, ID, and/or insurance information. It can also set different alerts for different medications and times.

Figure xxxx: Simple medical alerts and recording devices[3]

Blood Pressure/Pulse Monitors

Another device, as shown in Figure xxx that can help in early detection of patients’ heart problems is the blood pressure reader or pulse monitor device. Such device is designed with high accuracy and error detection techniques as well as fuzzy logic measurements. In addition, it contains a memory for keeping the measurements history for some time. It is obvious that such device can give an indication to his/her holder by the current situation especially elder people.

Figure xxx: Blood pressure monitoring device[4]

Wearable Insulin Pumps

Persons with Diabetes are given special care due to the criticality of their cases. A wearable insulin pump device is invited especially for them, e.g. see Figure xxxx. Such device has a catheter at the end of the insulin pump that is inserted through a needle into the abdominal fat of a person with diabetes.Dosage instructions areentered into the pump's small computer and the right amount of insulin is injected in a controlled manner. It will be more beneficial of such device can transfer the patient’s information to its treatment hospital at the same time to keep his/her record updated.

Figure xxx: Wearable insulin pump device

AMON - Advanced Telemedical Monitor

AMON is wireless monitoring system that is described at [5].The system includes a wrist-mounted Monitoring Device (WMD), as shown in Figure xxx,with different sensors such as heart rate, heart rhythm, 2-lead ECG, blood pressure, O2 blood saturation, skin perspiration and body temperature sensors. The device is a part of a system that uses these advanced bio-sensors to gather vital information, analyze it automatically using a built-in expert system, and transmit the data to a remote telemedicine centre, for analysis and emergency care, using GSM/UMTS cellular infrastructure.

Figure xxx: The wrist-mounted Monitoring Device

The “Digital Plaster”

The digital plaster shown in Figure xxx is a device meant to be embedded in ordinary plaster that includes sensors for monitoring health-related metadata such as blood pressure, temperature and glucose levels. The “digital plaster” contains a Sensium silicon chip, powered by a small battery, which sends data via a cellphone or PDA to a central computer database. If the results show any worrisome signs, patients and doctors alike would be notified of the change in the data patterns. This also planned to add a motion sensor to the device so it could additionally serve in the role of “granny monitor” by detecting things like falls or complete inactivity.

Figure xxxx: Digital plaster device [6]

  1. Health Care Applications/Prototypes

In this section, we will survey some of the current e-health applications. Some of these applications are very simple to implement. However, many others are complicated since they combine different types of networks and sensing devices.

4.1 Baby Care - Sleep Safe

Foremost among these risk factors is stomach sleeping. Numerous studies have found a higher incidence of Sudden Infant Death Syndrome (SIDS) among babies placed on their stomachs to sleep [8][9]. Stomach sleeping puts pressure on a child's jaw, therefore narrowing the airway and hampering breathing. A simple prototype (called SleepSafe) [7] detects the sleeping position of the infant. It alerts the parents when the infant is detected to be lying on its stomach, offering them peace of mind without having to constantly watch their child while it sleeps. This prototype architecture is shown in Figure aaa(a).

Figure aaa: SleepSafe baby monitor for detecting infant sleeping position [7]

The sensor mote attached to the infant’s clothing is a SHIMMER mote [14]. This mote has a 3-axis accelerometer; a single axis is used to sense the infant’s position relative to gravity. With the mote oriented “face-up” on the infant’s chest, 3 discrete positions (back, side, and stomach) are measured as anti-parallel, perpendicular, and parallel to the force of gravity. Figure aaa(b) illustrates how these positions are measured relative to gravity.

4.2. Baby Care - Baby Glove

As the weight of children decreases, the mortality rateincreases[10]. Many of these statistics are due in part to their extreme sensitivity to temperature fluctuations, which must stay within a consistent range of 36◦C to 38◦C. With these very tight restrictions, very sensitive, bulky and rather expensive devices are implemented to closely monitor vitals. An integrated health monitoring devicehas been developed, contained within a swaddling baby wrap (called The Baby Glove)[7].