Guidelines for Using Computerized Dynamic Posturography (CDP)

This video provides an overview of how to use Computerized Dynamic Posturography (CDP) for assessment purposes, with a focus on the Sensory Organization Test (SOT).

If you prefer reading, find the full transcript below.

Practical precautions

There are some important guidelines and recommendations to be aware of when performing computerized dynamic posturography (CDP).

1. Weight limit

The standard harness that is supplied with the CDP/IVR™ has an upper weight limit of 300 pounds. Alternative harnesses are available, for instance for pediatric use, or those who exceed this weight limit.

2. Shoes off

Patients should remove their shoes for the duration of their time on the CDP platform. It is recommended for hygiene purposes to use foot covers whenever standing on the CDP platform.

3. Attach harness loosely

The harness should be attached to the patient securely enough to support them should they fall, but relatively loosely in order to avoid restricting their movement and to avoid providing them with additional somatosensory feedback.

4. Patient may fall

It is important to be aware that the patient may fall, or step, when undergoing computerized dynamic posturography. The harness is there to protect them, and reassure them, however the clinician should also always position themselves behind the patient to reassure them of their presence, should they stumble.

5. Screen may move

In certain conditions, the screen may move. This is referenced to how much sway the patient has. In the sensory organization test (SOT), the CDP/IVR™ will provide a one-to-one ratio, which means the screen moves equally as much as the patient sways. This is called camera gain.

6. Platform may move

In certain conditions, the platform may move. This is again referenced to how much sway the patient has. In the SOT, the CDP/IVR™ will provide a one-to-one ratio, which means the platform moves equally as much as the patient sways. This is called sway gain.

7. Eyes open or closed

In different conditions, the patient will also be instructed to have their eyes either open or closed. As the patient will be facing the screen – and the clinician is unable to see the patient's face and eyes during testing – it's advisable to check with the patient after each trial that they did in fact maintain their eyes in the appropriate condition as instructed for the total duration of the trial.

SOT conditions

For the sensory organization test, there are six different conditions that need to be performed (Table 1).

Table 1: All six conditions with input disruption shown in italic.

Condition 1

Eyes open, still platform, static visual field

Condition one is really important to get right, so you might want to perform a practice run and delete it before starting the test properly to ensure the patient has understood the instructions. Condition one is the baseline against which the other conditions are calculated in order to get the sensory score ratios. So it's very important to get an accurate condition one recording.

Condition one is looking at whether the patient can stand still when they have all of the sensory inputs (vision, vestibular and somatosensory) available to them. So there's no reweighting process taking place here. We are just looking at how the patient performs in a very simple scenario.

Condition 2

Eyes closed, still platform, static visual field

Condition two is looking at what happens when vision is removed. Can the patient remain stable when their eyes are closed? Here, sensory reweighting is taking place and so they are relying on their somatosensory system as the main input, because they are still. However, there is still some vestibular input as well.

Condition 3

Eyes open, still platform, sway-referenced visual field

Condition three has the vision system back, as the eyes are open, but because the screen is sway referenced, the visual input is disrupted. Here, what we are investigating is whether the patient still prioritizes those disrupted, erroneous visual signals over and above the somatosensory and vestibular inputs.

Sensory reweighting should place the somatosensory and vestibular inputs as the priority inputs, but if the patient is over reliant on visual inputs because of their vestibular problem, then this can lead to problems in daily life.

Condition 4

Eyes open, sway-referenced platform, static visual field

In condition four, the somatosensory input is reduced because the platform is sway referenced. So in this condition, we are looking at whether the patient can prioritize and reweight the remaining inputs (the vision system and the vestibular system) and use these to help keep them stable and balanced.

Condition 5

Eyes closed, sway-referenced platform, static visual field

In condition five, vision has been completely removed because the patient's eyes are closed and the somatosensory input has been reduced, because the platform is sway referenced. And so the sensory integration process must reweight the vestibular system's input.

Condition five is looking at whether the patient can successfully prioritize the vestibular system and make use of the vestibular input signals to keep them stable.

Condition 6

Eyes open, sway-referenced platform, sway-referenced visual field

In the final condition, condition six, the patient has reduced somatosensory input because the platform is sway referenced and disrupted visual input because the screen is sway referenced. And so their sensory organization process should reweight the vestibular input as the priority.

Condition six is assessing whether the patient can successfully suppress the erroneous visual signals and make use of their vestibular signals in order to stay stable. Or are they over reliant on visual input because of a vestibular insult?

SOT instructions

When instructing the patient for the sensory organization test, you could give some initial instructions such as:

“The sensory organization test will determine how well you use your vision, the sensation in your feet and your inner ear to maintain balance. By challenging these three balance systems during the assessment, we can measure the effectiveness of each system in helping you keep your balance.”

It's important to explain each condition as you encounter them and instruct accordingly, considering especially whether the patient needs to keep their eyes open or closed. The instructions for each condition should be to:

“Try and stand as still as you can, trying not to move because the force plate underneath you is measuring the amount of sway that you have.”

At the end of each trial or condition, it's important to check whether they've managed to keep their eyes open, or closed, for the duration of the trial.

SOT key considerations

It is recommended to perform all three trials for each condition of the SOT, which will be averaged by the CDP/IVR™ into a composite score. It is vital to perform a minimum of two trials as the CDP/IVR™ will then average the two trials for the third trial. Without at least two trials, there will be no resultant calculation for that condition.

The normative data has been derived from data with shoes off, which is why the patient should remove their shoes during the assessment. It's recommended to look at the patient's feet during the different trials. This will tell you what is happening with regards to hip and ankle strategies.

Lastly, if you do not want to use a particular trial in the report, you must delete it immediately.