John Zaleski, Ph.D., CPHIMS

Time synchronization of medical device data: a straightforward example

The following slides were generated by this author and presented at the FDA Workshop on Interoperable Medical Devices in January 2010. Perhaps an esoteric but important challenge in patient care management and clinical research is the time alignment of data streams automatically collected from patient care devices (PCDs). Data collected from individual patient care devices may contain (1) local time stamps from the devices themselves that are not synchronized with common clocks; and, (2) queries of these patient care devices for their data may not be synchronized with independent queries for similar data from other patient care devices, resulting in data that are not synchronized with one another.

This case is illustrated in Figure 1 below in which a sampling of multi-parameter data collected from a patient who has undergone coronary artery bypass grafting surgery is being monitored in time. As can be seen the plots of individual parameters (again, only a small subset shown) describe the evolution over time.

Discrete data points show lack of time synchronization

In Figure 2, the individual data points from the separate patient care devices are overlaid on the continuous data, illustrating that these discrete points are not time synchronized in terms of their query or resulting output.

Data reporting at any particular instant illustrates time synchronization need for patient care device data

the plot of Figure 3 illustrates the need for time synchronization of patient care device data. Should a data request from all devices be made at a particular instant, certain data may be “stale.” That is, lack of time synchronization can result in data that are old or not current. If the query frequency of data associated with a patient care device not be aligned in time, then should a request for data be issued, the data that are available may be that which is valid at a previous time stamp.

Lack of time synchronization may impact clinical decision making

Figure 4 illustrates further the possible implication of lack of time synchronization: data staleness associated with misaligned or non existent data.

Alignment with absolute time also impacts time synchronization as each patient care device may not be using standard time clocks

Figure 5 illustrates a further complication to time synchronization: the lack of a common time clock. Should patient care devices not use or synchronize to common time standards (such as network time services within the enterprise), then the very real and common problem of time offsets will exist. The net effect of this is to cause a bias or shift offset of time in terms of data collection, making the process of time synchronization impossible to solve.

Hazards and risks associated with patient care devices whose data are not time synchronized

Figure 6 summarizes the potential hazards of receiving and using data from patient care devices whose data are not synchronized in time.

Clinical Decision Support impacts on non-time-synchronized patient care device data

Figure 7 summarizes the impacts of time synchronization on real-time clinical decision making.

The end state: time synchronization of patient care device data

Figure 8 illustrates the objective: when data from patient care devices are not available at a particular reporting time, provide the capability to “fill in the gaps” by querying for these data.

 Time synchronization summary

As a result of this workshop and other efforts, IHE (Integrating the Healthcare Environment) created a workgroup to begin to address what became known as Asynchronous Data Query (ADQ). The work of this group is to establish a common transaction for retrieving time-synchronized device data from patient care devices.

Other resources on this topic include my research at other locations on this site. Thanks for visiting http://www.medicinfotech.com.