react-native-ecg-utils

Mathematical library for working with ECG data from the Callibri sensor.

The main functionality is the calculation of cardio-interval lengths, heart rate and Stress Index (SI).

During the first 6 seconds the algorithm is learning, if no 5 RR-intervals are found in the signal 5 RR-intervals are not found, the training is repeated. Further work with the library is iterative (adding new data, calculating indicators).

Initialization

Determine the basic parameters

• Raw signal sampling frequency. Integer type. The allowed values are 250 or 1000.
• Data processing window size. Integer type. Valid values of sampling_rate / 4 or sampling_rate / 2.
• Number of windows to calculate SI. Integer type. Allowable values [20...50].
• The averaging parameter of the IN calculation. Default value is 6.

Creating a library instance

Firstly you need to determine lybrary parameters and then put them to library. Tne next step is initialize the filters. In the current version the filters are built-in and clearly defined: Butterworth 2nd order BandPass 5_15 Hz.

You can initialize averaging for SI calculation. It is optional value.

ReactNative (JavaScript)

// 1. Raw signal sampling frequency
let sampling_rate = 250;
// 2. Data processing window size
let data_window = sampling_rate / 2;
// 3. Number of windows to calculate SI
let nwins_for_pressure_index = 30; 
let math = new EcgMath(sampling_rate, data_window, nwins_for_pressure_index)
// Filters are initialized in the constructor

// optional
// 4. The averaging parameter of the IN calculation. Default value is 6.
let pressureIndexAverage = 6;
math.setPressureAverage(pressureIndexAverage);

Initializing a data array for transfer to the library:

The size of the transmitted array has to be of a certain length:

• 25 values for a signal frequency of 250 Hz
• 100 values for a signal frequency of 1000 Hz

ReactNative (JavaScript)

var samples: number[] = new Array(25)
// or
var samples: number[] = new Array(100)

Optional functions (not necessary for the library to work)

Check for initial signal corruption. This method should be used if you want to detect and notify of a distorted signal explicitly.

ReactNative (JavaScript)

if(math.isInitialSignalCorrupted){
    // Signal corrupted!!!
}

Work with the library

• Adding and process data:

ReactNative (JavaScript)

math.pushData(samples)

• Getting the results:

ReactNative (JavaScript)

// check for a new peak in the signal
if(math.isRRdetected){
    // RR-interval length
    console.log(math.RR)
    // HR
    console.log(math.HR)
    // SI
    console.log(math.PressureIndex)
    // Moda
    console.log(math.Moda)
    // Amplitude of mode
    console.log(math.AmplModa)
    // Variation range
    console.log(math.VariationDist)
    math.setRRchecked()
}

Finishing work with the library:

ReactNative (JavaScript)

math.clearData()
math.free()