biodex BioSway Operation Manual page 20

CONTENTS
4. The comprehensiveness of the test to address each of the systems that contributes to balance:
Visual, vestibular and somotosensory.
What is being measured during the CTSIB test?
• Stability Index
• Sway Index
Stability Index and Sway Index
The BioSway tracks the subjects sway angle and direction from center. This measure is called the
Stability Index. The Stability index is the average position from center. Specific information on
how the Stability index is calculated can be found in the appendix. The Stability index does not
indicate how much the patient swayed only their position. To quantify how much the person
swayed we use the standard deviation of the Stability index. This value we have called the Sway
Index.
For example:
If a patient is positioned in a manner that biases their placement from the center, the stability
index will be a large value. However, if the patient swayed very little the standard deviation
would be low. This is evident in the COG plots. A patient could have a score of equal 6.5, yet
standard deviation would only be .8 and the printout tracing would show they did not sway
very much. However, if they were positioned off-center, or even on-center – and swayed a lot -
the standard deviation would be higher. Thus the standard deviation is indicative of sway.
The Sway Index is an objective quantification of what commonly is done with a time-based
pass/fail for completing the CTSIB stage in 30 seconds without falling, or assigning a value of 1
to 4 to characterize the sway. 1= minimal sway, 4 = a fall.
The Sway Index is really the Standard deviation of the Sway Angle. The higher the Sway Index.
The move unsteady the person was during the test.
bioSway ctSIb normative data ranges for each condition.
Reliability and normative data are described in more detail in Appendix B.
CTSIB Normative Sway Index ranges are:
Condition 1: Eyes Open firm surface:
Condition 2: Eyes closed firm surface:
Condition 3: Visual conflict firm surface:
Condition 4: Eyes Open foam surface:
Condition 5: Eyes Closed foam surface:
Condition 6: Visual conflict foam surface:
If a patient cannot complete a condition, it is noted as "Fell" on results screen and report.
NOTE: Visual Conflict Eye Glasses: Clinicians that want to do the Visual conflict conditions will
require some type of glasses that provide a distorted yet transparent image. Commercially available Prism
type glasses are commonly used. Other improvised glasses are: 3D glasses, or clear safety glasses in which
the lenses have been marred or covered with Scotch™ type tape.
.21-.48
.48-.99
.46-.88
.38-.71
1.07-2.22
.84-1.47
— 4-5 — CLINICAL CONSIDERATIONS