heartbeat.go

package dsp

import (
	"fmt"
	"github.com/goccmack/godsp/peaks"
	"math"
)

type RPeaks struct {
	Indices             []int
	RPeakInterval       []float64
	HeartBeatsPerMinute []float64
}

func GetRPeaks(signal *Signal) RPeaks {
	// Assume that the highest heart rate is 200 BPM
	separator := signal.SampleRate / (200.0 / 60.0)

	indices := peaks.Get(signal.Signal, int(separator))

	rPeakInterval := make([]float64, 0)
	bpm := make([]float64, 0)

	previousTime := 0.0

	// Calculate the r-peak interval
	for i := range indices {
		currentTime := float64(indices[i]) * (1.0 / signal.SampleRate)

		t := currentTime - previousTime

		rPeakInterval = append(rPeakInterval, t)
		if t == 0 {
			bpm = append(bpm, 0)
		} else {
			bpm = append(bpm, 60/t)
		}

		previousTime = currentTime
	}

	return RPeaks{
		Indices:             indices,
		RPeakInterval:       rPeakInterval,
		HeartBeatsPerMinute: bpm,
	}
}

func (r *RPeaks) IsRPeak(index int) bool {
	for i := range r.Indices {
		if r.Indices[i] == index {
			return true
		}
	}

	return false
}

func (r *RPeaks) Avg() int {
	if len(r.HeartBeatsPerMinute) == 0 {
		return 0
	}

	sum := 0.0
	for i := range r.HeartBeatsPerMinute {
		sum += r.HeartBeatsPerMinute[i]
	}

	return int(sum / float64(len(r.HeartBeatsPerMinute)))
}

func (r *RPeaks) Count() int {
	return len(r.HeartBeatsPerMinute)
}

func (r *RPeaks) HeartRateVariabilityByRmssd() float64 {
	totalSamples := len(r.RPeakInterval)

	if totalSamples == 0 || totalSamples == 1 {
		return 0
	}

	total := 0.0

	for i := 0; i < totalSamples-1; i++ {
		diff := (r.RPeakInterval[i+1] * 1000) - (r.RPeakInterval[i] * 1000)

		total += diff * diff
	}

	result := math.Sqrt(total / float64(totalSamples-1))

	return result
}

func (r *RPeaks) String() string {
	return fmt.Sprintf("Total heart beats detected: %v, avg heart rate: %v BPM", r.Count(), r.Avg())
}