Metrics & Definitions

This document defines the metrics calculated and displayed by the application, including the specific time windows used for calculation.

Heart Rate (HR)

• Definition: The frequency of heart contractions.
• Unit: Beats Per Minute (bpm).
• Calculation:
  • The displayed Heart Rate is not the instantaneous value from the sensor.
  • It is a median of the last 5 beats.
  • This filtering removes outliers (missed beats or artifacts) while remaining responsive to rapid rate changes.

Heart Rate Variability (RMSSD)

• Definition: Root Mean Square of Successive Differences between heartbeats.
• Unit: Milliseconds (ms).
• Calculation:
  • Input: Raw RR intervals (ms) provided by the hardware sensor (e.g., Polar H10).
  • Window: The application calculates rolling averages simultaneously for 1, 5, 15, and 60-minute windows.
  • Filtering: None. All intervals, including premature beats (PVCs) and artifacts, are included.

Note: Because no filtering is applied, this metric represents "total rhythm variability" rather than just autonomic tone.

Baevsky Stress Index

• Definition: A geometric measure of heart rate variability derived from the histogram of RR intervals.
• Unit: Index units (arbitrary scale, typically 50-1000).
• Calculation:
  • Window: Calculated over a 1-minute rolling window of RR intervals.
  • Update Frequency: Updated every time a new QRS complex is detected by the internal Pan-Tompkins algorithm.
• Interpretation (Visualized Zones):
  • 0 - 150 (Green): Normal State. Balanced autonomic regulation.
  • 150 - 500 (Yellow): Moderate Stress. Increased sympathetic tone or exertion.
  • 500+ (Red): High Stress. Significant strain on regulatory systems.

Beat Morphology Clustering

• Definition: The grouping of heartbeats into clusters based on their waveform shape.
• Calculation:
  • Window: Analyzes ECG data from the last 60 seconds.
  • Update Frequency: The clustering algorithm re-runs every 5 seconds.

Activity Recognition

• Definition: Automatic classification of physical activity based on device motion.
• Source: Android Activity Recognition API (utilizing phone sensors).
• States: Still, Walking, Running, Cycling, Driving.
• Usage:
  • Real-time display on the dashboard.
  • Automatic annotation in data streams to correlate heart rate changes with exertion.

RR Interval

• Definition: The time elapsed between two successive R-waves (heartbeats).
• Unit: Milliseconds (ms).
• Source: Directly reported by the BLE sensor.