Wireless body area networks: What engineers need to know

In recent years, we’ve witnessed the emergence of body area network technology for remote patient monitoring. BAN development has been driven by pressure to reduce health care costs, and by an increased focus on prevention and early risk detection.

Market studies predict demand for BAN devices will reach an annual volume of 100 million units by 2011, driven by wearable and implantable devices for use in patient monitoring, as well as for consumer health and fitness.

Given the aging population in many regions, the monitoring aspect of health care represents an important piece of the puzzle, especially in countries where the availability of clinicians is the fundamental capacity limitation of the system. A system that continuously monitors the condition of elderly patients, sharing the information with remote care providers, can better cope with health care demand. This is particularly true when health care and elder care providers strive to allow senior citizens with chronic conditions to live independently for as long as possible.

BANs are highly localized wireless networks that can potentially support a variety of medical applications, from tracking vital signs to monitoring the functioning of implants and performing state-of-the-art endoscopic exams.

Traditional patient monitoring consists of physiological sensors connected between a patient’s body and a dedicated signal processing unit located nearby through unwieldy wires. Those wires limit the patient’s mobility and comfort, and some studies suggest they can be a source of in-hospital infections. Moreover, motion artifacts from the connected wires can negatively affect the measured results.

With the advent of low-power and low-cost wireless connectivity technologies, BANs can now be implemented and deployed using available complementary technologies. Figure 1 illustrates a typical wireless BAN.

Figure1. A typical body area network. Click on image to enlarge.

 
 
 

A network of sensors is placed on or close to the surface of the patient’s body or implanted statically into tissue to enable the collection of specific physiological data. Such an arrangement allows for the continuous monitoring of a patient’s health regardless of the person’s location. Sensed signals can be those for electroencephalography (EEG), electrocardiography (EKG), electromyography (EMG), skin temperature, skin conductance and electrooculography (EOG).

Each of the sensors transmits collected information wirelessly to an external processing unit, located on the patient or at the patient’s bedside. The processing unit can then use traditional data networks, such as Ethernet, Wi-Fi or GSM, to transmit all information in real-time to a doctor’s device or a specific server. The sensors used in a BAN generally require accuracy for their physiological parameter of interest and a certain level of low-power signal processing as well as wireless capability.

In some instances, the sensors can be transceivers or receivers, depending on the bandwidth of the data to be collected—for instance, temperature or heart rate data, vs. an analog EKG waveform.

Sensors used in BANs can be classified into two main categories, depending on their operation mode.

Wearable BANs usually comprise sensors that are attached to the surface of the body or implanted very close to the surface of the body for short periods of time (less than 14 days). They typically consist of inexpensive, lightweight and small sensors that allow unrestricted ambulatory health monitoring to provider near-real-time updates on the health status of the patient.

Implantable BANs have sensors that are located deeper in the body, in areas such as the heart, brain and spinal cord. Implantable BANs meld active stimulation and physiological monitoring, and represent a highly desirable proposition for some chronic conditions that until now have only been treatable using drugs. Examples of such treatments include deep-brain stimulation for Parkinson’s disease, spinal stimulators for chronic pain and bladder stimulators for urinary incontinence.

An understanding of BAN requirements is key to the design of reliable products in this space. BANs are characterized by easily configured, low-cost, ultralow-power and highly reliable sensor systems. Their packaging and operation must be sterile for use in proximity to or inside a human body. In addition, the wireless communication must be robust against RF interference in the environment from such sources as Wi-Fi networks, microwave ovens and cordless phones.