Knowledge Base

Definition

Dependent variable with two possible values (0 and 1) calculated from an imported data signal, resampled to the same sample rate as the EthoVision XT sample rate. The value of the state variable is calculated per sample from the values of the corresponding resampled variable, relative to one or two thresholds.

Top: Heartbeat. Bottom: Heartbeat state, defined in the Analysis profile as "Heartbeat > 400 bpm, with Downsampling= Mean value, Upsampling= Last value, Averaging interval =1". For clarity, it was renamed to Heartbeat state: hb >400.

How to Specify an External Data Variable "State"

1. Click the Add button next to the [data set name] state.
2. Under Select, choose the Downsampling method (default: Mean value) and the Upsampling method (default: Last value).
3. Under Outlier filter, select the Averaging interval (default: 1). See Averaging interval in External data (resampled).
4. Under State threshold, specify that the state is scored when the Signal is:
   • above (>=) or below (<=) a threshold value x.
   • within a range (>= x and <= x) or outside a range (<= x and >= x).
   Enter the thresholds you require.
5. Complete the procedure to add the variable.
6. Plot Integrated Data, or calculate the statistics.

The resulting state (frequency and duration) is much dependent on what you choose as downsampling/upsampling methods.

Below: Effect of different upsampling methods on a state variable Temperature state. Original temperature signal sampled every minute. Variables resampled at 25 Hz. The state variable is scored when the resampled value is >= 30 ºC, using the methods Last value, Linear interpolation, Missing value, and Zero value. Note that Temperature state in cases 4 and 5 gives very short states, because most of the data points in the corresponding Temperature resampled variable are missing or zeros, respectively.

NOTE: When calculating states, if the sample with a valid variable value is followed by missing samples, EthoVision XT keeps the calculated value of the state for the next three missing samples.

Below: Zoomed-in view of the previous picture for Temperature state upsampled with Missing value, and Temperature state upsampled with Zero value, around 240 s. A state is scored when the resampled value is >= 30 ºC. For simplicity, Averaging interval = 1. When calculating states, if the value of the resampled variable is followed by missing values, like in Temperature - "Missing", the calculated value of the state is kept for the next 3 samples. This is the reason why the Temperature state - "Missing" around time 240 s lasts 4 samples. In the case of upsampling with Zero value, the state is assigned only to the current sample.

How to Retrieve States from an Imported Signal

In the following example, the file containing the data set Phase with possible values 1, 2 and 3 is imported.

If you want to retrieve the original states with their duration:

1. In the Analysis profile, define three Phase state variables, and rename them to, for example, Phase 1, Phase 2, and Phase 3.
2. For each state variable, set the appropriate thresholds. For example, for Phase 1: Signal is <= 1.5.
3. Plot the variables to compare them with the original signal.

From top to bottom: original signal, resampled signal, states calculated using thresholds. Right: threshold for Phase 1.

Source: EthoVision XT 19 Help, Noldus Information Technology