Respiratory rate

Question

Hi,
I have a data acquisition vi. I dislay respiration signals and trying to calculate respiratory rate per minute. In order to calculate RPM(respiratory perminute) I’ve used a threshold peak detector. I calculate the difference of the index of the first peak and the index of the second peak,the result generates the number of total samples between two consecutive counts. To count respiratory rate I divided the sample rate by the number of samples per breathing.Then I’ve multipiled the result by 60 to generate RPM.
I ‘ve put the width value for the threshold detector 30.
You can see the frontpanel of my vi and diagram as attachment.
The problem is everything is ok while fast breathing however, while breathing slowly the difference of the index of the first peak and the index of the second peak(you can see in the front panel as x-y ) is negative. Thus the RPM is negative.Also the RPM values lower than 30 is always negative.
What should I do?
Attachments:
bre soru.JPG ‏51 KB

Answer 1

After doing some analysis, this approach helps some, but maybe not enough to help you.
Essentially the Hilbert Transform does the following. Perform an FFT on your signal, negate the negative frequency values and perform an inverse FFT to get back to the time domain. This relates and even signal to its corresponding odd counterpart (i.e. the Hilbert transform of a cosine signal is a sine signal and vice versa).
Here is a procedure that works for the simulated data that I have.
1. Subtract the value of the first point of data from all of your data to make your first point equal to zero.
2. Use a Butterwork Filter (filter type = Bandpass, order = 2, fh = .1, fl = 0.005) to filter your data (Advanced Analysis->Filters).
3. Use the Derivative function to take the derivative of your data (Advanced Analysis -> Time Domain)
4. Use the Peak Detect function to capture the peaks (Advanced Analysis -> Time Domain)
This will hopefully enhance the peaks in your respiration data making it easier to capture them with the peak detection function.
If you have data you can send me to work with I can see if it works well. I am using LabVIEW 7.1 so I will attach a JPG of the code.
Randall Pursley
Attachments:
respire.JPG ‏58 KB