Updated with several time-domain calculations for evaluating Heart Ra…

PulseSensorAmped_Arduino_1dot4/AllSerialHandling.ino

@@ -20,10 +20,27 @@ void serialOutputWhenBeatHappens(){
  Serial.print("*** Heart-Beat Happened *** "); //ASCII Art Madness
  Serial.print("BPM: ");
  Serial.print(BPM);
- Serial.print(" ");
+ Serial.print(", IBI: ");
+ Serial.print( IBI );
+ Serial.print( ", NNDelta: " );
+ Serial.print( RRDelta );
+ Serial.print( ", SDNN: " );
+ Serial.print( SDNN );
+ Serial.print(" || HRV: ");
+ Serial.print( int( LN20RMSSD ) );
+ Serial.print(" (RMSSD: ");
+ Serial.print( RMSSD );
+ Serial.print( "), SDSD: " );
+ Serial.print( SDSD );
+ Serial.print( ", NN50: " );
+ Serial.print( NN50 );
+ Serial.print( ", pNN50: " );
+ Serial.print( PNN50 );
+ Serial.println( " " );
  } else{
- sendDataToSerial('B',BPM); // send heart rate with a 'B' prefix
- sendDataToSerial('Q',IBI); // send time between beats with a 'Q' prefix
+ sendDataToSerial('B',BPM); // send heart rate with a 'B' prefix
+ sendDataToSerial('Q',IBI); // send time between beats with a 'Q' prefix
+ sendDataToSerial('H', int( LN20RMSSD ) ); // send HRV with a 'H' prefix
  } 
 }
 
@@ -39,8 +56,8 @@ void sendDataToSerial(char symbol, int data ){
 
 // Code to Make the Serial Monitor Visualizer Work
 void arduinoSerialMonitorVisual(char symbol, int data ){ 
- const int sensorMin = 0; // sensor minimum, discovered through experiment
-const int sensorMax = 1024; // sensor maximum, discovered through experiment
+ const int sensorMin = 0;  // sensor minimum, discovered through experiment
+ const int sensorMax = 1024;  // sensor maximum, discovered through experiment
 
  int sensorReading = data;
  // map the sensor range to a range of 12 options:
@@ -50,7 +67,7 @@ const int sensorMax = 1024; // sensor maximum, discovered through experiment
  // range value:
  switch (range) {
  case 0: 
- Serial.println(""); /////ASCII Art Madness
+ Serial.println("");  /////ASCII Art Madness
  break;
  case 1: 
  Serial.println("---");

PulseSensorAmped_Arduino_1dot4/Interrupt.ino

@@ -1,17 +1,14 @@
-
-
-
-volatile int rate[10]; // array to hold last ten IBI values
-volatile unsigned long sampleCounter = 0; // used to determine pulse timing
-volatile unsigned long lastBeatTime = 0; // used to find IBI
-volatile int P =512; // used to find peak in pulse wave, seeded
+volatile int rate[61]; // array to hold last 61 IBI values
+volatile unsigned long sampleCounter = 0; // used to determine pulse timing
+volatile unsigned long lastBeatTime = 0; // used to find IBI
+volatile int P = 512; // used to find peak in pulse wave, seeded
 volatile int T = 512; // used to find trough in pulse wave, seeded
 volatile int thresh = 525; // used to find instant moment of heart beat, seeded
 volatile int amp = 100; // used to hold amplitude of pulse waveform, seeded
 volatile boolean firstBeat = true; // used to seed rate array so we startup with reasonable BPM
 volatile boolean secondBeat = false; // used to seed rate array so we startup with reasonable BPM
-
-
+volatile int successiveRRDeltas[60]; // used to track differences between successive RR values
+ 
 void interruptSetup(){ 
  // Initializes Timer2 to throw an interrupt every 2mS.
  TCCR2A = 0x02; // DISABLE PWM ON DIGITAL PINS 3 AND 11, AND GO INTO CTC MODE
@@ -24,22 +21,23 @@ void interruptSetup(){
 
 // THIS IS THE TIMER 2 INTERRUPT SERVICE ROUTINE. 
 // Timer 2 makes sure that we take a reading every 2 miliseconds
-ISR(TIMER2_COMPA_vect){ // triggered when Timer2 counts to 124
+
+ISR(TIMER2_COMPA_vect){ // triggered when Timer2 counts to 124
  cli(); // disable interrupts while we do this
  Signal = analogRead(pulsePin); // read the Pulse Sensor 
  sampleCounter += 2; // keep track of the time in mS with this variable
  int N = sampleCounter - lastBeatTime; // monitor the time since the last beat to avoid noise
 
-  // find the peak and trough of the pulse wave
+ // find the peak and trough of the pulse wave
  if(Signal < thresh && N > (IBI/5)*3){ // avoid dichrotic noise by waiting 3/5 of last IBI
- if (Signal < T){ // T is the trough
- T = Signal; // keep track of lowest point in pulse wave 
+ if (Signal < T){  // T is the trough
+ T = Signal;  // keep track of lowest point in pulse wave 
  }
  }
 
  if(Signal > thresh && Signal > P){ // thresh condition helps avoid noise
- P = Signal; // P is the peak
- } // keep track of highest point in pulse wave
+ P = Signal;  // P is the peak
+ }  // keep track of highest point in pulse wave
 
  // NOW IT'S TIME TO LOOK FOR THE HEART BEAT
  // signal surges up in value every time there is a pulse
@@ -50,10 +48,14 @@ ISR(TIMER2_COMPA_vect){ // triggered when Timer2 counts
  IBI = sampleCounter - lastBeatTime; // measure time between beats in mS
  lastBeatTime = sampleCounter; // keep track of time for next pulse
 
+ int i;
  if(secondBeat){ // if this is the second beat, if secondBeat == TRUE
  secondBeat = false; // clear secondBeat flag
- for(int i=0; i<=9; i++){ // seed the running total to get a realisitic BPM at startup
- rate[i] = IBI; 
+ for(i=0; i<=60; i++){ // seed the running total to get a realisitic BPM at startup
+ rate[i] = IBI; 
+ }
+ for( i=0; i<59; i++){ // seed the successiveRRDeltas array with 0s
+ successiveRRDeltas[i] = 0;
  }
  }
 
@@ -64,21 +66,96 @@ ISR(TIMER2_COMPA_vect){ // triggered when Timer2 counts
  return; // IBI value is unreliable so discard it
  } 
 
-
- // keep a running total of the last 10 IBI values
- word runningTotal = 0; // clear the runningTotal variable 
-
- for(int i=0; i<=8; i++){ // shift data in the rate array
- rate[i] = rate[i+1]; // and drop the oldest IBI value 
- runningTotal += rate[i]; // add up the 9 oldest IBI values
+ for( i=0; i<=59; i++){ // update rate array. shift data
+ rate[i] = rate[i+1]; // and drop the oldest IBI value 
+ }
+ rate[60] = IBI; // add the latest IBI in the rate array
+
+ // calculate a running total of the last 10 IBI values
+ word runningTotal = 0; // clear the runningTotal variable 
+ for( i=51; i<=60; i++ )
+ {
+ runningTotal += rate[i];
  }
-
- rate[9] = IBI; // add the latest IBI to the rate array
- runningTotal += rate[9]; // add the latest IBI to runningTotal
  runningTotal /= 10; // average the last 10 IBI values 
  BPM = 60000/runningTotal; // how many beats can fit into a minute? that's BPM!
  QS = true; // set Quantified Self flag 
  // QS FLAG IS NOT CLEARED INSIDE THIS ISR
+
+ // HRV Analysis
+ // https://en.wikipedia.org/wiki/Heart_rate_variability#HRV_analysis
+
+ for( i=0; i<=58; i++){ // update successive RR difference array. shift data
+ successiveRRDeltas[i] = successiveRRDeltas[ i + 1 ];
+ }
+ successiveRRDeltas[59] = rate[ 60 ] - rate[ 59 ]; // set the newest RR difference as the last entry in the array
+
+ RRDelta = successiveRRDeltas[59]; // store the newest RR difference
+
+ // SDNN: the standard deviation of NN (RR) intervals.
+ // alternate calculation method for stdDev without a second loop may be possible:
+ // https://en.wikipedia.org/wiki/Algorithms_for_calculating_variance#Online_algorithm
+ double tVal = 0; // temp utility variable to be re-used in loops
+ double aveRR = 0; // calculate the average RR value.
+
+ for( i=1; i<=60; i++){ // add up the last 60 RR values and divide by 60
+ aveRR += rate[ i ]; // (Don't include the first entry or you'll add 61 values)
+ }
+ aveRR /= 60;
+
+ for( i=1; i<=60; i++){ // calculate the standard devation of RR intervals
+ tVal = aveRR - rate[ i ]; // using the average that was just calculated
+ SDNN += tVal * tVal;
+ }
+ SDNN = sqrt( SDNN / 60 );
+
+ // SDSD: standard deviation of successive differences 
+ // The standard deviation of the successive differences between adjacent NNs (RRs).
+ SDSD = 0;
+ int aveRRDelta;
+ for(int i=0; i<=59; i++) // find the average of successive differences
+ {
+ aveRRDelta = successiveRRDeltas[ i ]; 
+ }
+ aveRRDelta /= 60;
+
+ for(int i=0; i<=59; i++) // calculate the standard deviation of successive differences
+ { // using the average that was just calculated
+ tVal = aveRRDelta - successiveRRDeltas[ i ];
+ SDSD += tVal * tVal; 
+ }
+ SDSD = sqrt( SDSD / 60 );
+
+ // RMSSD: root mean square of successive differences
+ // The square root of the mean of the squares of the successive differences between adjacent NNs (RRs).
+ RMSSD = 0;
+
+ for(int i=0; i<=59; i++) // square each successive RR difference
+ { // take the sum of all the values
+ tVal = successiveRRDeltas[ i ]; // divide by the total sample size to get the mean
+ RMSSD += tVal * tVal; // and take the square root
+ }
+ RMSSD = sqrt( RMSSD / 60 );
+
+ LN20RMSSD = 20 * log( RMSSD ); // take the natural log of RMSSD
+ // then scale the result so the range is linear and values 
+ // fall approximately on the scale of 0-100. 
+
+ // NN50: the number of pairs of successive NNs (RRs) that differ by more than 50 ms.
+ NN50 = 0; // add all the successive differences that are greater than 50ms
+ for(int i=0; i<=59; i++)
+ {
+ if( abs( successiveRRDeltas[ i ] ) > 50 )
+ {
+ NN50 ++; 
+ }
+ }
+
+ // pNN50: the proportion of NN50 divided by total number of NNs (RRs).
+ PNN50 = NN50 / 60; // divide the total number of successive differences greater than 50s
+ // that were found and divide by the total sample size to get the 
+ // percent of successive differences greater than 50s.
+
  } 
  }
 

PulseSensorAmped_Arduino_1dot4/PulseSensorAmped_Arduino_1dot4.ino

@@ -10,6 +10,9 @@ This code:
 
 Read Me:
 https://github.com/WorldFamousElectronics/PulseSensor_Amped_Arduino/blob/master/README.md 
+
+Updated with HRV display by Elliot Mebane, Roguish, Inc. Feb 2016
+HRV requires 1 minute of data before it's accurate. 
  ---------------------- ---------------------- ----------------------
 */
 
@@ -26,6 +29,14 @@ volatile int IBI = 600; // int that holds the time interval between
 volatile boolean Pulse = false; // "True" when User's live heartbeat is detected. "False" when not a "live beat". 
 volatile boolean QS = false; // becomes true when Arduoino finds a beat.
 
+volatile int RRDelta = 0;
+volatile double RMSSD = 0;
+volatile double LN20RMSSD = 0;
+volatile double SDNN = 0;
+volatile double SDSD = 0;
+volatile double NN50 = 0;
+volatile double PNN50 = 0;
+
 // Regards Serial OutPut -- Set This Up to your needs
 static boolean serialVisual = false; // Set to 'false' by Default. Re-set to 'true' to see Arduino Serial Monitor ASCII Visual Pulse