CDP Best Practices Update: Clinical Considerations for Using New Bertec Norms
Introduction
In this blog post we’ll highlight how Bertec’s advances in balance assessment technology affect the data obtained during CDP assessments and how it relates to normative data (norms) for the sensory organization test (SOT). We’ll highlight the differences between Bertec’s norms and historical norms for the SOT, answer questions regarding the data compatibility with that obtained on historical devices for the SOT and ADT, and present recommendations to aid in clinical decision-making.
Bertec’s Advanced Technology
The primary technical differences between the NeuroCom and Bertec CDP systems affecting the assessment results include force plate differences and the immersive visual surround of the dome.
Force plate considerations
The Bertec force plate sampling frequency of 1000 times per second and its higher natural frequency result in significantly different sway energy scores used in calculating the Adaptation Test (ADT) scores. Therefore, it is likely that the Bertec and NeuroCom ADT scores differ significantly. The Motor Control Test (MCT) latency scores are based on detecting rapid center of pressure changes during the semi-automatic postural reflex response. During the typical latency interval of 120-140 milliseconds, the Bertec system’s 1 millisecond resolution eliminates any errors in latency scoring and results are comparable to those obtained on the NeuroCom.
Clinical Implications: MCT results are interchangeable with those obtained on the NeuroCom due to the greater number of samples collected during the latency interval. ADT results obtained on the Bertec demonstrated greater sway than on the NeuroCom. Sway scores for the toes up condition in the 70-79 year age group were higher than all other age groups (20-69 years). Since research hasn’t examined how Bertec’s higher frequency force responses affect the ADT results differently than those obtained on the NeuroCom, we recommend selecting the Bertec normative data set to pay special attention to the sway responses for the TU condition and risk of fall, especially in elders. Qualitative visual analysis of each trial provides an indication of whether central adaptation is occurring over time.
Immersive visual surround
In the Bertec system, the sensation of visual motion is generated by scenes that are projected onto the fixed, fully immersive dome of the Bertec CDP. During the CDP assessments subjects experience standing in a tube-like tunnel without horizontal or vertical reference points and no distant horizon. During SOT3 and SOT6, the walls appear to move with the degree of COG sway, requiring the subject to suppress inappropriate visual cues. In contrast, the box-like moveable enclosure of the NeuroCom system had visible horizontal and vertical edges and a horizontal scene reference that provided visual cues as a visual anchor. This enclosure moved as a unit in response to the subject’s sway. The way that visual conditions and visual motions are generated is completely different between the two systems.
Clinical Implications: Individuals who experience visual discomfort in the Bertec system may display lower SOT1 scores relative to SOT2 as closing their eyes relieves the discomfort. SOT4 scores may also be lower in these individuals because there is no possibility to compensate with vision due to a lack of a horizontal or vertical visual anchor in the scene. Therefore, the Bertec may be more sensitive in assessing impairments in effectively using visual cues for postural control. Second, individual responses to Bertec’s SOT3 and SOT6 may be more provocative in those with visual sensory impairments, visual preference, or visual motion sensitivity. A low visual preference score is an indicator of difficulty in resolving visual conflict: the individual relies on visual information even when that information is incorrect, resulting in visual motion sensitivity. The immersive virtual reality scenes and fully customizable parameters allow the clinician to design targeted training programs in the CDP to treat visual motion sensitivity.
Sensory Organization Test: Bertec Normative Values
The new Bertec normative values are classified by decade, ranging from 20-79 years of age. The new Bertec norms for vestibular sensory score ratios are not significantly different between the oldest and youngest age groups (20-79 years), potentially making it easier to detect even small vestibular impairments with the Bertec SOT. However, historical norms should be used for those who fall outside the 20–79-year age range.
In those who are suspected of balance problems related to impairments in using vision for balance, SOT1 and SOT4 scores may be lower. Those with a visual preference (i.e. the degree to which one relies on visual information even when that information is incorrect because of the inability to suppress inappropriate visual cues) will respond differently to SOT3 and SOT6.
In developing the Bertec norms, strict exclusion criteria were utilized, resulting in similar SOT vestibular ratio scores between the eldest and youngest groups. Therefore, Bertec norms may be more sensitive in detecting vestibular impairments. Second, the Bertec normative data sets demonstrate smaller minimal detectable change (MDC) scores for composite and individual sensory conditions, meaning that the Bertec norms are better able to identify treatment effects. However, the clinician should keep in mind that larger vestibular score differences for SOT5 and SOT6 are required to document change due to treatment. This contrasts with the stable platform where small changes in the scores are clinically significant. These detailed MDC values for each sensory condition, in addition to the composite score MDC value of 6.5 points, are unique to Bertec’s norms and provide valuable information to aid in treatment decisions.
When compared with clinical outcome measures, the Bertec SOT is moderately correlated with the non-instrumented dynamic visual acuity test (DVA) and the functional gait assessment—indicating an interaction between postural control, gaze stability, and walking in those with vestibular impairments. Combining the Bertec SOT with the Bertec Vision Advantage computerized assessment of gaze stability and dynamic visual acuity will yield more data upon which to base clinical decisions.
Final Thoughts
Technological advances in force plate technology and immersive virtual reality combined with the results of normative studies of the Bertec SOT have demonstrated greater sensitivity in detecting impairments related to the use of visual information, resolving visual conflict, and lower MDC values, suggesting that the Bertec CDP / IVR™ is more sensitive to smaller treatment effects than the NeuroCom. Normative data are based on three trials per condition; therefore, we recommend performing all three trials. The clinician may consider re-testing patients who present with significant anxiety, fear of falling, and loss of confidence, common in those with vestibular dysfunction. Regardless of the normative data set selected, the clinician should follow the same test protocol for sequential testing including set up, foot placement, harness use, standardized instructions, and performing three trials per condition. Finally, the data obtained by the SOT can be used to design fully customizable immersive virtual reality training programs targeted to address sensory impairments.
For more detailed information, contact Bertec Sales: [email protected].
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References
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Grove, C. R., Whitney, S. L., Hetzel, S. J., Heiderscheit, B. C., & Pyle, G. M. (2021). Effect of Repetitive Administration of a Next-generation Sensory Organization Test in Adults with and without Vestibular Dysfunction. Otology & neurotology: official publication of the American Otological Society, American Neurotology Society [and] European Academy of Otology and Neurotology, 42(3), e363–e370. https://doi.org/10.1097/MAO.0000000000002950
Heinrichs, K. I. (2024). CDP Best Practices Update: New Bertec Norms. Bertec Corporation, Columbus, Ohio.
Nashner, L. M. (2019). Understanding Normative Values for CDP: A Comparison of Bertec Balance Advantage and Neurocom Equitest Systems. Bertec Corporation, Columbus, Ohio.
Quintana, C., Heebner, N. R., Picha, K. J., Andrews, M. L., Abt, J. P., & Hoch, M. C. (2021). Test–retest reliability and methodological considerations of the sensory organization test in healthy young adults. Athletic Training & Sports Health Care, 13(3), 103-110.
Trueblood, P. R., Rivera, M., Lopez, C., Bentley, C., & Wubenhorst, N. (2018). Age-based normative data for a computerized dynamic posturography system that uses a virtual visual surround environment. Acta oto-laryngologica, 138(7), 597–602. https://doi.org/10.1080/00016489.2018.1429653
