R/InterpolateNIHR.R

In RHRV: Heart Rate Variability Analysis of ECG Data

InterpolateNIHR <-
function(HRVData, freqhr=4, method= c("linear", "spline"),
         verbose=NULL) {
# -------------------------------------
# Interpolates instantaneous heart rate
# -------------------------------------
#	freqhr -> frequency for interpolating heart rate
#	method -> "linear" interpolation or "spline" monotone interpolation

  method = match.arg(method)
  HRVData = HandleVerboseArgument(HRVData, verbose)

	VerboseMessage(HRVData$Verbose, 	
		paste("Interpolating instantaneous heart rate"))
	VerboseMessage(HRVData$Verbose, 	
	               paste("Frequency:", freqhr, "Hz"))
	
	HRVData$Freq_HR=freqhr

	first = head(HRVData$Beat$Time,1)
	last = tail(HRVData$Beat$Time,1)
 	npoints=as.integer((last-first)*HRVData$Freq_HR+1)

 	VerboseMessage(HRVData$Verbose, 	
 	               paste("Number of beats:", length(HRVData$Beat$niHR)))
 	VerboseMessage(HRVData$Verbose, 	
 	               paste("Number of points:", npoints))
 	
 	
 	if (method == "linear") {
 	  fun = approxfun(HRVData$Beat$Time,HRVData$Beat$niHR,
 	                  method = "linear", ties = "ordered")
 	} else {
 	  fun = splinefun(HRVData$Beat$Time,HRVData$Beat$niHR,
 	                  method = "monoH.FC", ties = "ordered")
 	}
 	
 	vectorxint=seq(first,last,1/HRVData$Freq_HR)
 	
 	HRVData$HR=fun(vectorxint)
 	
 	# limit indicates the maximum width in seconds of an interval without beats
 	limit = 30 # seconds
 	# beg and end are the beginning and end of the interval without beats
 	begindex = which(diff(HRVData$Beat$Time)>limit)
 	beg = HRVData$Beat$Time[begindex]
 	end = HRVData$Beat$Time[begindex+1]
 	
 	# the value of HR in these intervals is set to zero
 	if (length(begindex) > 0) {
 	  for (i in 1:length(beg)) {
 	    HRVData$HR[vectorxint>beg[i] & vectorxint<end[i]] = 0
 	    warning("interval without beats detected!")
 	  }
 	}
 	
 	return(HRVData)
}