Patient monitor human interface design

Hewlett-Packard Journal, Oct, 1991 by Gerhard Tivig, Wilhelm Meier

Depending on the Component Monitoring System configuration and the user's choice, the resting display shows four, six, or eight real-time waveforms of the measured parameters with the digital values derived from the waveforms displayed next to them. For better vertical waveform resolution, up to two groups of waves can share a larger sector on the screen. This overlapping of waveforms allows the user to correlate different waveforms on the time axis.

Each waveform channel can be assigned a different speed. TWo presentation modes of the waveforms are possible: either the waveforms are fixed on the screen and old waveform samples are erased by the newest, or the waveforms move across the screen with the newest samples always next to the digital values.

The content of each channel can be configured. Additionally, the user has the choice of three preconfigured screens to make it possible to adapt quickly to changes of the patient's condition.

Digital, Values

The user has definite expectations about where, when, and in what format digital values should appear. The requirements for the arrangement of the digital values were:

* The values of a parameter plugged into a rack or turned on should show up automatically. It is unacceptable to have to position the value of such a parameter manually. It must appear in the right position.

* The digital values must be placed next to their corresponding waveform if possible.

* As many values as possible have to be shown with large digits. On a full display it is acceptable for the less-important values to be shown with small digits, but not on a display with just two measured parameters.

These requirements are met by an elaborate algorithm. It is an iterative, process that tries to find a place for all digital values available in the system. It first places all values next to their waveforms with large digits. It then places all other values, according to a priority list, in the right column next to the waveform values. Temperature values are first assigned large digits.

If there are still unassigned numerics left but no more space available, the algorithm starts decreasing values in size, starting with those of lowest priority, and repeats the process. As a last resort, temperature values are allowed to share the same place, alternating at two-second intervals.

Operating Concept

The general operating structure of the Component Monitoring System human interface is described by the state diagram shown in Fig. 4.

Keypad. After the keys on the parameter modules, which are mainly used to enter the menus and adjust parameter settings, the keypad underneath the screen is the main tool for users to interact with the monitor. Mg. 5 shows this keypad. As mentioned above, a handheld keypad for remote operation has some additional functions available.

The first row of keys on the keypad consists of seven function keys. Their functions are defined by the menus that appear on the screen.

The next row of keys is used to enter six different categories of monitor interaction.