Cardiovascular Signals
Cardiovascular signals are the foundation of stress detection. Heart rate and heart rate variability (HRV) provide the most reliable real-time indicators of autonomic nervous system activity — the body's stress response system.
Accepted Fields
| Field | Type | Unit | Description |
|---|---|---|---|
heart_rate | float | BPM | Instantaneous heart rate (40-220) |
rmssd | float | ms | Root mean square of successive RR differences — primary HRV metric |
sdnn | float | ms | Standard deviation of NN intervals — overall HRV |
pnn50 | float | % | Percentage of successive intervals differing by >50ms |
mean_ibi | float | ms | Mean inter-beat interval |
ibi_count | int | — | Number of inter-beat intervals in the sample window |
spo2 | float | % | Blood oxygen saturation (90-100) |
How It Works
When you send cardiovascular data via /v1/ingest, Nefesh validates the values against physiological ranges, applies proprietary signal processing to filter noise and artifacts, and fuses the result into the unified stress score.
Higher heart rate combined with lower HRV (RMSSD, SDNN) indicates sympathetic nervous system activation — the body's fight-or-flight response. Nefesh detects this pattern in real-time and adjusts the stress score accordingly.
Compatible Devices
- Polar H10 — chest strap, RR intervals via Web Bluetooth
- Apple Watch — heart rate via HealthKit
- Garmin — HR + HRV via Connect IQ
- Any device that outputs heart rate or RR intervals
Example Payload
{
"session_id": "sess_abc123",
"timestamp": "2026-03-30T14:30:00Z",
"heart_rate": 82,
"rmssd": 34.5,
"sdnn": 48.2,
"source_device": "polar_h10"
}Cardiovascular signals are fused in v1 and contribute directly to the stress score. They carry the highest weight among all signal categories due to their strong correlation with autonomic stress response.