How to calculate power in specific frequency band

Question

Hi Everyone. I have been trolling on here for months but this is my first post so I hope I am putting this in the correct place.
What I am trying to do is simple in theory but I have tried over and over and am having no luck in getting this to work. I wish to calculate the power in specific frequency bands for heart rate variability analysis.
Referring to the article "Using LabVIEW for Heart Rate Variability Analysis"  http://zone.ni.com/devzone/cda/epd/p/id/5832 I am aware of the steps I need to follow.
I have plotted the RR intervals and resampled these with cubic spline interpolation to give a nice time dependent series. I then wire this to a PSD VI and this is where I am out of my depth.
I know from the above article that I am looking for power in these frequency bands
VLF  
ms2
Power from 0–0.04 Hz.
LF  
ms2
Power from 0.04–0.15 Hz.
HF
ms2
Power from 0.15–0.4 Hz.
The NI Biomedical Startup kit can do these, however I am unable to look into the source code as I do not have some required plugins in my installation. I have LabVIEW 8.6 full development system.
As this is not my area there is a steep learning curve and I have read many forum posts and pages but am still unsure of what I need to do here.
It is my understanding that the frequency resolution is simply the sample rate/number of samples. So if I require a resolution of 0.01Hz then theoretically 100Hz sample rate and 10,000samples would give me this.Furthermore I gather that the size of the output array from the PSD VI is equal to the # of data points (This i have just noticed from trial and error so I may be wrong).
Therefore if I am using the above values then is it correct that PSD would return an array and all I need to do is simply sum the contents of those array elements to get the power?
For example if frequency resolution is 0.01 , then to get power from 0-0.04Hz I must simply add the first 4 elements in the PSD output array?
I have made a test VI to show what I am talking about and attached it to this post.
Some feedback on the required approach would be a lifesaver here. I have purchased a couple of books and read through pages of forum posts but am still having trouble with this.
Many thanks!
Attachments:
labviewhelp.jpg ‏53 KB

Answer 1

Sorry about that, I didn't realize you wanted to run the code too The VI was doing a bunch of other stuff so I have tried to clean that out and just leave the relevant bit. As mentioned above, the case block executes when a peak is detected in the data and appends this value to an array.
I am using the technique of resampling the data because this is what was mentioned in this http://zone.ni.com/devzone/cda/epd/p/id/5832 and also in another reference that I have been following titled "Heart Rate Variability Standards of Measurement, Physiological Interpretation, and Clinical Use" http://circ.ahajournals.org/cgi/content/full/93/5/1043 which states
"The spectrum of the HRV signal is generally calculated eitherfrom the RR interval tachogram (RR durations versus number ofprogressive beats; see Fig 5a,b) or by interpolating the DES,thus obtaining a continuous signal as a function of time, orby calculating the spectrum of the counts–unitary pulsesas a function of time corresponding to each recognized QRS complex.35Such a choice may have implications on the morphology, themeasurement units of the spectra, and the measurement of therelevant spectral parameters. To standardize the methods used,the use of RR interval tachogram with the parametric method,or the use of the regularly sampled interpolation of DES withthe nonparametric method may be suggested; nevertheless, regularlysampled interpolation of DES is also suitable for parametricmethods. The sampling frequency of interpolation of DES mustbe sufficiently high that the Nyquist frequency of the spectrumis not within the frequency range of interest."
Attachments:
Exp-PulseOximeter.vi ‏205 KB