Virtual Corset™

The Virtual Corset™ has been described as "a gentle reminder to stand up straight". A more erect posture can reduce trunk muscle activity, and may reduce the loads borne by the spinal column.

By combining an inclinometer, data logger and silent vibrating alarm in a tiny pager enclosure, the Virtual Corset™ keeps track of trunk inclination, and warns the wearer when a prescribed inclination angle limit has been reached. The clinician or therapist sets the unit's inclination limits, sample frequencies, and data save intervals using the serial port of a personal computer (PC); once programmed, the Virtual Corset may be disconnected from the PC. In the field, it performs its pre-programmed datalogging and biofeedback tasks while worn anywhere: during work, play, exercise, and rest.

U. S. Patent 5887351 and Patents Pending

General Documentation

• Virtual Corset™ Manual

Scientists at the University of Vermont (Krag et al, RESNA, Pittsburgh, 1997) performed studies using the Virtual Corset™. Their study contained two main objectives: 1) to provide a clinical measure of the effect of limiting trunk motion through the use of feedback (using the Virtual Corset™) on patients with low back pain, and 2) to compare these results to those obtained through the use of a traditional cloth corset and no cloth corset. Seventeen persons with mechanical low back pain were recruited to participate. The Virtual Corset™ was used as the feedback device. The Virtual Corset's bin frequency (or sample rate) was set at 2 samples per second, at 2˚ increments in 1 hour Bin save intervals (data segments). Using this configuration, subjects were able to use the Virtual Corset for about 10 days of continuous data collection (for prototype Virtual Corset with only 64 K bytes memory).

Shown above are two typical graphs constructed from Virtual Corset™ data from this study. Figure 1 is an illustration of a histogram with percent of total wear time on the Y axis and trunk angle on the X axis. The data can also be manipulated to look at other aspects of activity as illustrated in Figure 2, with percent of total time on the Y axis and trunk angle on the X axis. Figure 2 shows one subject's typical daily trunk inclination patterns for each day in a one week period.

The results suggested that feedback is as good or better than traditional cloth corsets at helping the user maintain a more neutral posture with less total exposure to extreme flexion angles. Longer term studies are now underway to determine if the use of feedback (to encourage more erect postures and to reduce exposure to trunk inclination) can also reduce the amount of back pain.

Data adapted from: (1) Krag M.H., Fox, J.R., McDonald, L.P.: "Evaluation Of Biofeedback Device In Reducing Pain and Improving Function Of Individuals With Low Back Pain", presented to Rehabilitation Engineering Society of N. America, Pittsburgh, PA, 1997

The Virtual Corset™ provides biofeedback to enhance one's awareness of their trunk inclination, while simultaneously saving inclination data for future interpretation.

Data are saved as histograms; each histograms' sum represents the total count of trunk inclination angles measured at the programmed sample rate (binning frequency). Binned data are very useful in reducing the datalogger's requisite memory; once collected, these histogram data are easily downloaded over the serial port for analysis. The Virtual Corset™ logs inclination in 1˚ increments (factory set) over ±180 in the flexion extension axis and ±70 degrees on the lateral bending axis. The sample rate for data collection is termed the binning frequency; as data is collected, the unit builds a histogram of inclination over specified time intervals (bin save interval) and then saves this histogram to memory. The process is repeated until the Virtual Corset™ is turned off or the memory capacity is reached. Note that the data (and programming parameters) are saved in non-volatile memory, and will not be lost in the event of power down or low battery capacity.

The bin save interval can be programmed for any amount of time, however, longer intervals provide lower resolution of the wearer's activity. For example, if the bin save interval were set at one hour, at the end of the day there would be 24 histograms showing the wearer's trunk inclination angle at the period of the binning frequency. This would show a histogram of inclination for each hour over the course of a day. If the bin save interval were set at 12 hours, at the end of a day there would be only 2 histograms of inclination. Longer bin save intervals use less memory than shorter bin save intervals, but longer bin save intervals provide less information about daily activities.

Below we provide a summary of Virtual Corset™ key term definitions:

• Inclinometer: sensing instrument which measures the angle of a body with respect to gravity
• Data Logger: portable micro computer with data storage and data downloading capabilities
• Binning frequency: how often the inclinometer is interrogated to bin the inclination angle, for example, once per second
• Bin save interval: how often the histogram is saved to memory, for example, once per hour