Introduction to the HP Component Monitoring System - fourth-generation patient monitoring system - includes related article on medical expectations of monitors

This fourth-generation patient monitoring system offers a set of hardware and software building blocks from which functional modules are assembled to tailor the system to the application and the patient.

Over the past twenty years HP has been a supplier of patient monitoring equipment to the healthcare industry. Patient monitors are observational and diagnostic tools that monitor physiological parameters of critically ill patients. Typical parameters include the electrocardiogram (ECG), blood pressure measured both invasively and noninvasively, pulse oximeter (SaO[sub.2] and respiratory gases, among others. The catalog of parameters is still growing based on the need for better patient care and the technical feasibility of new measurement techniques.

Patient monitors are used in a variety of departments within hospitals. These include operating rooms, intensive care units, cardiac care units, in-hospital and out-of-hospital transportation, and special function areas such as lithotripsy and x-ray. A patient monitoring system must be versatile and applicable to most of these areas. This means that it must support a wide range of configurations and allow quick adaptation to the patient-specific level of care. For a normal appendectomy, monitoring the ECG, noninvasive blood pressure, SaO[sub.2], and one temperature will suffice. At the other extreme, during a cardiovascular operation as many as eight different physiological parameters will be measured.

The HP Component Monitoring System is designed to meet these requirements. This article outlines the high-level project goals and the approaches taken to meet them. It also describes the overall hardware and software architecture of the HP Component Monitoxing System. Subsequent articles in this issue highlight the technical contributions of the Component Monitoring System project in more detail.

Design Goals

The HP Component Monitoring System is the fourth generation of patient monitors to be designed and built by the HP Medical Products Group. Based on our experience, current customer needs, and expected future trends in the medical field, two objectives were viewed as areas in which HP could make a major contribution. One is the area of modularity and flexibility and the other is ease of use.

Modularity and Flexibility. The monitor is composed of the following functional modules:

* Data acquisition

* Parameter signal processing

* Monitor control and data input

* Display

* System connects.

Each of these functional modules is implemented in a set of hardware and software building blocks, which as a whole form the Component Monitoring System depicted in Mg. 1. Separating the monitor into its generic elements provides many advantages. First, the monitor can easily be configured to best meet the application needs of the individual customer. Parameters can quickly be combined according to the required level of care and changed when necessary. Second, adding functionality to a monitor is as simple as inserting the appropriate hardware into an existing unit and updating the software if necessary.

A third advantage is that the Component Monitoring System can be kept abreast of new technological trends by enhancing or redesigning the appropriate functional element. Implementation will only affect one building block, and will be fully backward compatible with existing systems.

Finally, production has been dramatically simplified. Customization of each monitor is the last integration step in production. Thus, all components can be assembled and tested without knowing the specific configuration in which they will be used.

Flexibility is enhanced by designing the monitor components so that their physical location can be optimized to address ergonomic considerations and by allowing the user to program the monitor's default settings and standard configuration. This means that the monitor can be adapted to a wide range of current and future clinical applications.

Ease of Use. Ease of use is of particular importance for patient monitors in operating rooms and critical care units, where clinicians use patient monitors to make informed decisions about potentially life-threatening situations. In the past, clinicians have had to strike a compromise between the desired functionality of a patient monitor and its ease of use. Our goal was to make this very sophisticated piece of equipment truly intuitive for doctors and nurses to use. Other areas that we focused on, and that played an important role during the development phase were:

Implementation of methods to meet HP quality goals.

* Minimization of production costs and support for a linear cost profile. This means that functionality can be segmented down to its generic building blocks. Should a particular feature be needed, the customer pays for it and nothing more.

* Standardization, ranging from uniform design tools and software development environments all the way to minimizing the number of different electrical components used in the Component Monitoring System as well as the number of mechanical parts needed to assemble the unit.

System Architecture

From an architectural standpoint the Component Monitoring System can be divided into three segments (see Fig. 2):

* Module rack with parameter modules

* Computer module

* Displays.

The module rack and parameter modules represent the interface to the patient. Each parameter module is dedicated to the measurement of one or more physiological signals, and is housed in a separate enclosure. Within the parameter modules, the transducer signals are electrically isolated from ground potential, amplified, sampled, and converted from an analog to a digital format. The digital parameter values together with the status of each module are polled at fixed intervals and sent to the computer module for further interpretation.

Up to eight single-width modules fit into one module rack. The module rack can be either an integral part of the computer module or totally detached, in which case it would be called a satellite module rack. The satellite module rack is connected to the computer module by an umbilical-cord-like cable, which carries both the digital signals and a 60V de power line for the parameter modules. One computer module can support as many as four satellite module racks. This concept allows the user to position the parameter modules as close as possible to the patient, where the signal is measured. The transducer cables can thus be kept short, minimizing the amount of wiring as well as the tendency for it to become tangled or draped over the patient.

Computer Module

The computer module is the main processing unit. It consists of a cardcage that can house up to 23 function cards and one dc-to-dc converter Fig. 3). Function cards currently available include CPUs, memory cards, interface cards, display controllers, and a utility card. For the first release, a total of 11 function cards were designed. The interconnection within the cardcage takes place via the central plane, a motherboard located in the middle of the chassis with press-fit connectors mounted on both sides of a printed circuit board. Data exchange between the function cards takes place on the message passing bus. This bus is routed to aU 23 slots on the central plane, allowing a high degree of freedom as to where a function card can be inserted. The message passing bus is the backbone of the Component Monitoring System. Many of the goals listed above only became possible with the help of this communication concept.

The basic function of the message passing bus is that of a broadcast system. Each message sent on the bus consists of a header, which describes the content, and the actual data. A source (e.g., a CPU card) will obtain control of the message passing bus and transmit its information. The data is not transmitted in a point-to-point fashion from one source to one receiver. Instead, message passing bus data is transmitted without any specific destination, and it is up to the function cards to watch for the information needed by their applications. As. soon as a card detects a match between a header it is looking for and the header of the message on the bus, it automatically puns this data into an internal stack.

The activities of bus arbitration, transmission, header matching, and data reception are controlled by the message passing bus chip. One of these interface chips is located on each function card that actively takes part in the communication process. The chip was designed specifically for the Component Monitoring System. It also was the first HP production ASIC application-specific IC) to be designed using a silicon compiler tool.

A more detailed description of the message passing bus concept and the design of the interface chip can be found in the article on page 10, which covers the Component Monitoring System hardware architecture.

Displays

The customer can choose either a monochrome or color high-resolution display. Multiple independent displays can be used to present different sets of information to specific user groups. For example, the surgeon needs a different presentation of patient information than the anesthesiologist during surgery.

Physically separating the display from the computer module gives the user a choice of screen sizes and the possibility of mounting the computer module at a remote location when space next to the patient is at a premium.

The user interacts with the monitor through a combination of hardkeys and softkeys on the display keypad or through a remote keypad which functionally duplicates the keys on the display bezel.

Software Modularity

The concept of a modular system also applies to the software architecture (see Fig. 4). Application-specific modules represent the basic budding blocks out of which the total solution can be assembled. The ECG application, for example, including the signal interpretation, alarm handling, and control interaction, is all encapsulated in one module. To the surrounding environment these application software modules are totally self-contained packages, and only exchange information with one another via the message passing bus. By virtue of this concept, it is possible to link each module as an independent entity with any of the other modules and assign it to one of the Component Monitoring System CPU cards.

A more detailed description of the software architecture can be found in the article on page 13.

All of the Component Monitoring System software is stored on EPROM function cards. These cards are physically located next to a CPU, and the applications running on that CPU execute directly from the adjacent memory card. All other CPU cards in the monitor get their application software downloaded into the on-board RAM during boot time. The advantage of this solution is that installing software is as easy as inserting one EPROM card.

Summary

The Component Monitoring System has proved that the concept of component modularity can be extended far beyond the mere ability to mix and match parameter modules. Modularity in this system means that the customer can tailor the patient monitor to best fit the application all the way from the parameters that need to be registered to the displays and interfaces the system should incorporate. The Component Monitoring System can also grow with the user's needs over time, and thus secure the hospital's assets for many years.

The success of the modularity concept is reflected in the fact that some of the hardware and software elements have found their way into other medical devices manufactured by HP. Overall, the Component Monitoring System architecture has proven it can function as a monitoring platform for years to come.

Acknowledgments

The design of the Component Monitoring System has been a team effort involving at times up to 50 engineers located at the Waltham and Boblingen Medical Divisions. All of these individuals and many others deserve recognition for their hard work to make this product a success. I would also like to thank all who contributed to this series of articles on the Component Monitoring System. Besides the authors of each chapter, and the numerous unnamed supporters, one person deserves particular recognition: Heike Schreiber. Her continued enthusiasm and devotion helped to make this issue of the HP Journal possible.

COPYRIGHT 1991 Hewlett Packard Company
COPYRIGHT 2004 Gale Group