Medical Device Link.

Originally Published MEM Spring 2003

EMBEDDED SYSTEMS

With the Internet in nearly every household, it's no wonder that it's finding its way into the development of home healthcare medical devices.

Howard A. Raphael

Medical monitoring at home is more common than ever. The demand for remote monitoring has driven the development of devices and systems to fill this need. Moreover, the data gathered remotely must be communicated to medical personnel. Traditional store-and-forward applications such as Holter monitors, repertory monitoring, blood analysis, and other such non-life-threatening data acquisitions were done with modems built into an instrument or a docking station at a patient's residence. A modem connection provided clinicians with feedback for analysis and, in some cases, the ability to communicate adjustments, dosages, and results back to a patient. However, these data often needed third-party processing or dedicated processing hardware and software to extract relevant data.

Higher-performance digital signal processors (DSPs) and microprocessors were necessary to compact and preprocess the data. These processors could run more-sophisticated software such as signature analysis programs. Using the Internet, the data could be sent and received in a user-friendly format to any Internet-enabled PC via e-mail.

The missing link in the old system was a new type of component modem called an Internet modem, or iModem for short. Medical instruments that have built-in iModems are capable of bi-directional e-mail traffic. The medical PC terminal needs no special software because the e-mail sent from the instrument is preformatted. Should this data need to be extracted from the e-mail and processed or placed in a patient's file, a Windows-based software program can do this function unsupervised or automatically.

When designing an iModem, the Internet becomes the networking scheme that enables the instruments in the field to communicate with their respective hosts. No special networking technology is required because communications are based on the Internet's simple mail transfer protocol (SMTP), the industry standard for Internet e-mail. Basic e-mail messaging functionality is created when SMTP is combined with a mail retrieval protocol, such as POP3. When this capability is designed into a product, that product can become a networking element of the Internet. Because iModems cost about the same as traditional component modems, the additional capabilities add little to the design cost of the product. An iModem is a self-contained intelligent subsystem that can operate transparently and independently of its host instrument. The iModem allows the host to send or receive e-mail messages and route test e-mail messages to fax or voice messaging services using available machine-type Internet service providers (ISPs). Messages can be exchanged with PCs or with other instruments that have iModems.

Internet Service Providers

Modems connect to the Internet through an ISP using a local-access telephone number. Internet modem–based instruments can use an existing private corporate ISP or a general-purpose commercial ISP. Such instruments can now use a special machine ISP with unique amenities for Internet-enabled machines. Along with features such as text-to-voice messaging and text-to-voice file preprocessing, machine ISP is specifically designed for machine e-mail of large numbers of machine users. This function greatly enhances a device's capabilities and is, therefore, preferable to existing commercial ISPs.

Monthly access fees for a commercial ISP can range from $9 to $20. Machines use only e-mail (i.e., no Web browsing), which requires less access time and bandwidth of the ISP. ISP customer support is minimal for machines. Machine users in a group are all identical, so once a problem is solved for one, it is solved for all machines in the group. Machine ISP monthly access fees can be as low as $2 per month for basic service. A fixed monthly communications cost is often lower than variable telephone tariff usage charges associated with standard modems.

Embeddable Component

Figure 1. Basic functional blocks of an Internet modem include: intelligent microprocessor(µP), basic modem V90 element and modem interface, serial input/output (I/O) port and unique hardware I/O structure, and a telephone line interface. (click to enlarge)

An iModem is an embeddable component. As such, it is designed to be integrated into an instrument at the printed circuit board level like any other component or subsystem. An iModem has the following basic functional block elements (see Figure 1):

• Intelligent microprocessor (µP).
• Basic modem V.90 element and modem interface.
• Serial input/output (I/O) port and a unique hardware I/O structure, all generally running on 5 V.
• Data access arrangement (DAA), which provides a telephone line interface.
• Internet modem functional block diagram.

The combination of the modem and DAA components form the equivalent of a standard V.90, 56 Kb/sec modem. The SMTP firmware that allows the modem access to the Internet is part of the microcontroller. The I/O facilities are used to integrate the device symbiotically into the instrument. The host product's microprocessor communicates with the iModem through the modem's serial interface. These serial I/O facilities can also be used for receiving and sending e-mail.

Other designated I/O lines can be used for event-initiated actions, such as sending a prestored or casually composed e-mail message upon some event. Dedicated I/O facilities can also be used for resident sensor inputs, actuator outputs, or status line inputs. A single outgoing e-mail can transmit both the state of the certain input lines as communicable information and a text message. Incoming e-mail text can be used to activate and control output functions, alter displays, update product software, or provide text-messaging communications.

I/O Flexibility

An iModem can operate in two modes: autonomous event-driven mode or host-supervised control mode. Event-driven e-mail occurs when a hardware action triggers a predetermined e-mail response. For example, a contact closure can be programmed to initiate the sending of an e-mail message to a predefined e-mail address. Both pieces of information—the address and the message—can be stored in the iModem ready for the event to initiate the message.

Host-driven operation requires interaction between the iModem and the products host microprocessor. All iModems use special macro commands to control the iModem's operation. For example, an iModem uses "@T" as a command, similar to the "AT" commands of standard modems. Like AT commands, the unique Internet commands have macro-specific functionality. With host-supervised control, some aspect of the e-mail transfer is under the control of the host via the macro commands. Unlike event-driven operation where SMTP variables are fixed and stored in the iModem, the variables are dynamically changed and provided by the host's microprocessor for each communication. Each message will be different and each can have a different Internet address destination or origin.

Connecting to the Internet

Figure 2. Internet modem operational environment. (click to enlarge)

Each iModem connects to the Internet using unique e-mail identity parameters stored within its microcontroller firmware. These parameters, like a PC's e-mail software, operate transparently with the OEM's host software. Figure 2 shows the information ports to an iModem and the required user supply parameters. For all Internet connectivity, an iModem must have a unique identifier (a device ID number) programmed into the component modem with predetermined variables such as the following:

• Unique password.
• ISP access telephone number.
• Mail server hex address.
• Unique local e-mail Internet address for incoming e-mail.
• Destination Internet address unique to outgoing e-mail.

Figure 3. Unique macro commands used to control an Internet modem. (click to enlarge)

These variables are used to create a unique identifier for an iModem and the message being sent. This information is required to route the message from one server to another through the Internet and to its ultimate destination. The variables are programmed into the iModem using the unique set of AT-style commands (see Figure 3). (The Cermetek iModem uses "@T" to differentiate Internet commands from regular "AT" modem commands.)

Like all component modems, the commands are provided in serial form using the V.24 interface from the product's host microprocessor. Each variable is embodied in a separate command. The @T command, like the AT commands of a normal modem, give the user complete flexibility in controlling all operations.

When the modem begins an SMTP transfer, it acts autonomously of the product's host microprocessor. The correct address structure has been preformatted for the outgoing e-mail message or for the POP3 mail retrieval, the local-access number is dialed and, after the ISP connection is made, the log-on and password protection function is performed, completing the log-in. However, because this process does not always go as planned, a log-in attempt may fail. The iModem must be enough robust to recover from this failure and reattempt the connection, transparent to the host.

Conclusion

Through simple e-mail, an iModem creates the opportunity to add user-friendly communication capabilities, to medical instrumentation. The hardware needed is inexpensive and easy to integrate. To further extend iModem capabilities ISPs with machine-specific features now exist to provide gateways to the Internet.

To assist product designers, software development tools are also available. Such tools allow for easy configuration of an individual or group of iModems. This Internet-enabled technology allows designers to increase their medical product's functionality and utility. It also reduces cost and adds value.

Bibliography

Wood, David. Programming Internet Email. (Sebastopol, CA: O'Reilly and Associates, 1999).

Howard A. Raphael is president for Cermetek Microelectronics Inc. (Sunnyvale, CA). He can be reached at 408-752-5000 or sales@cermetek.com.

Illustration by EYEWIRE

Copyright ©2003 Medical Electronics Manufacturing