Medical Electronic Cable Assemblies
By John C. Colwell, Bishop & Associates Inc.

In 2007, medical cable assemblies accounted for approximately 35 percent of the total value of connector factory shipments to the medical electronics industry, or an estimated $386 million. This value is expected to grow in excess of 11 percent, reaching $430 million in 2008. Unlike most other industry sectors, where the ratio of the value of connectors applied to cable assemblies vs. total connector consumption is stable, the ratio of connectors applied to medical cable assemblies, compared to total medical connector consumption, is on the rise. This trend is attributable to the changing mix of cable assembly types and evolving circumstances of use within the medical electronics industry.

There are various ways to analyze the medical cable assembly market, for example, by form factor or type of construction, as shown below.

Looking deeper into the applications environments of the various types of cable assemblies, we find additional levels of characterization. Broadly speaking, medical cable assemblies can also be classified as equipment and sub-system interfaces, communications interfaces, and patient interfaces.

Equipment and sub-assembly interfaces include those cable assemblies that are installed as original equipment and typically remain in place for the life of the equipment. Examples would be harness assemblies found in a nuclear imaging device or, in the consumer world, a refrigerator. Except for equipment retrofits and upgrades, these assemblies are rarely replaced.

Communication interfaces include industry-standard serial cable assemblies, such as EIA RS-232, 422, 423, and 485 types, modular LAN interconnects EIA/T568 A/B types and fiber optic types. These cable assemblies are occasionally replaced when equipment is either rearranged or relocated within the facility.

Patient interfaces, or patient cables, include those cable assemblies that physically connect the patient to an electro-medical instrument for diagnostic or therapeutic purposes. As such, most patient cables are subject to periodic replacement throughout the course of the equipment life. Depending on the replacement frequency, the aftermarket value of patient cables can far exceed the value of the original equipment market. For a variety of reasons, the replacement frequency for several types of patient cables is increasing. To examine this trend, we must look a bit deeper into the classifications of patient cables.

Long-life/Expendable patient interface cables are designed for long life. However, it is generally accepted that most of these cables will be replaced several times during the life of the equipment. Cable assemblies are occasionally upgraded for performance reasons, or they become damaged from use and/or abuse. Such cable assemblies include ultrasound imaging transducer cable assemblies (shown right), ECG diagnostic and stress test cables, EEG diagnostic patient cables, defibrillator coil cord assemblies, MRI field coil cable assemblies, and control pendant assemblies.

Generally, cable assemblies in this category are custom designed for high reliability and long life. Specialty wires and cordage, designed for flexibility and wear resistance, are commonly employed in conjunction with well designed, bonded strain reliefs. Not only are these assemblies designed for reliability, they are also designed for ease of use. The optimal design is often a delicate compromise. A stiff, one-inch diameter ultrasound transducer cable would probably withstand being run over by the wheel of a heavy cart, but it would also make the ultrasound technician’s job difficult, if not impossible. It is for this reason that cable assembly manufacturers who specialize in medical assemblies have been so successful. They understand the environment.

Limited-use disposable patient cables include ICU/CCU monitor cables, ECG diagnostic leads, oxymeter cable assemblies, and similar types. Limited-use disposable assemblies are cable assembly types that are generally exposed to wear and tear in the application environment. For example, a 10-lead, ECG diagnostic patient cable typically consists of an interconnection yoke attached to a connectorized bulk cable and a set of 10 individual leads. The leads tend to deteriorate from exposure to mechanical stresses and cleaning solvents, resulting in faulty readings and the waste of valuable technician time.

A scheduled replacement of such assemblies is the preferred course of action, and also reduces labor costs and risk of failure.


Use-once disposable patient cables include catheters (right), electro-surgical knife assemblies, electro-surgical (dispersive) return electrodes, external pacing lead sets, surgical monitoring cables, fetal monitoring cables, neural stimulator lead sets, and other similar devices. For each of the various types of procedures performed in operating rooms, catheter labs, and delivery rooms, it has long been the practice to provide all of the instruments and accessories required for the procedure in a pre-packaged sterilized kit, assembled elsewhere in a six-sigma quality environment. That same concept is now beginning to be applied to use-once disposable cable assemblies. The bottom line is that the labor-cost of cleaning, sterilizing, and maintaining cable assemblies in a sterilized state for future re-use exceeds the initial cost of the assembly.

There is also a migration from some limited-use disposable cable assemblies to use-once types, as illustrated by the disposable pulse oxymeter shown at left. Instead of clipping onto a fingertip, the disposable type is more securely applied with medical tape. The finger-clip type, while reusable, tends to fall off the patient, resulting in false alarms at the nursing station and the need to dispatch someone to the patient’s location to re-apply the clip. The stay-on disposable device eliminates these unnecessary costs and distractions.

There are risk factors as well. Electro-surgical dispersive return electrodes collect and safely return the RF energy to the generator, thereby preventing hazardous leakage paths to ground. Traditionally, this was a two-piece assembly consisting of a disposable pad and a limited-use cord assembly. There were two points of interconnection: at the pad and at the generator. Increasingly, today’s return pads are provided with the return cable permanently attached, thereby eliminating the possibility of an inadvertent disconnect during surgery.

Moreover, hospital patient deaths as a result of nosocomial infections, specifically methicillin-resistant staphylococcus aureus (MRSA), are rising. This is forcing the health care industry to re-evaluate many of its cleaning and sterilization practices.

At the same time, the connector industry is beginning to focus on this shift towards limited-use and use-once disposable assemblies. Amphenol has introduced its Pulse-Lok^TM Series of limited use and disposable circular connectors (below left). W.W. Fischer Connector has introduced its L.U.C. ^TM line of disposable circular connectors designed for patient cable and similar applications (below right).

ODU has introduced its MEDI-SNAP ^TM line of circular disposable connectors (right). Other manufacturers of disposable medical connectors include Positronics, Lemo, and others.

These connectors are nonmagnetic, making them suitable for MRI applications. The number of mating cycles varies by manufacturer, from a very limited number of matings, to as many as 5,000 mating cycles.

Most disposable medical connector manufacturers have developed their own efficient, in-house cable termination capabilities. This enables them to furnish medical equipment OEMs with connectorized cord assemblies on a highly cost-effective basis.

John Colwell Director, Telecom, Medical and Instrumentation, Bishop & Associates Inc. John Colwell’s background includes 10 years at Nortel Networks‑Cable Group, where he directed the U.S. premises cable marketing effort. In addition, Colwell directed Nortel's global product development group. Prior to joining Nortel, Colwell held positions in engineering, business planning and development at Amphenol Corporation.