topic Re: calculating lung volume from airflow signal in Life Science

calculating lung volume from airflow signal

burcu — Sun, 16 Jan 2005 22:41:29 GMT

Hi,
I'm acquiring airflow signal. But I want to calculate and display volume from airflow signal. In order to do this I know I want to take the integral of airflow signal. My sample rate is 250 Hz.My acquired airflow signal is attached . I've tried to use Integral x(t) function in order to do this.I put 0.004(1/250) to dt.And I didn't wire anything to initial condition and final condition. But I couldn't get the desire lung volume signal. Could anyone help me please?

Re: calculating lung volume from airflow signal

rpursley8 — Mon, 17 Jan 2005 02:31:15 GMT

What is wrong with the signal? Why do you think you aren't getting what you expect? The integral works as expected. You might try truncating your data so that it starts at a zero value. What kind of values are you expecting?

Re: calculating lung volume from airflow signal

burcu — Tue, 18 Jan 2005 14:05:54 GMT

the peaks are too sharp in the integrated signal.In the attachment the second wiindow displays integrated signal. And the third one displays delayed integrated signal and the peas are round.I want to see like the third one.
I found at a publication that(which I taken the attachment http://www.biopac.com/AppNotes/app181intairflow/airflowint.htm)
It says:

To synchronize the two signals, you can enter a Maximum cycle period. The Maximum cycle period will allow you to set the length of the delay. By controlling the delay, you can add an additional calculation channel that will allow you to delay the flow signal by the same time period.

Do you have any recommendations to see integrated signal like the third one.Where and how should I put delay?

Thanks

Re: calculating lung volume from airflow signal

falkpl — Tue, 18 Jan 2005 14:20:37 GMT

Another quick and dirty method of integrating a "realtime" trace of data is to simply sum the data and multiply it by the delta time. If the data has a very high order function or lots of noise or sharp peaks this will not give you an accurate result. Increasing the data acq rate will also give you a more accurate integration of the signal. The integral is simply the sum over time of the F(t)*dt where the dt can be seen 1/sample rate and the signal data is your f(t). The computational over head for such a result is very fast; use the sum array for the last set of data and multiply it by the elapsed time (number of points * 1/sample rate) to yield an integration in sample units*seconds. If you need a more accurate approximation of the integral you can still use the integration VIs.

-Paul

Re: calculating lung volume from airflow signal

burcu — Tue, 18 Jan 2005 15:23:54 GMT

thanks for your reply.

Re: calculating lung volume from airflow signal

rpursley8 — Wed, 19 Jan 2005 04:30:14 GMT

When I do the following

Re: calculating lung volume from airflow signal

rpursley8 — Wed, 19 Jan 2005 04:30:55 GMT

I get these results. Is this what you get?

Re: calculating lung volume from airflow signal

burcu — Sat, 22 Jan 2005 23:14:06 GMT

Hi, yes this is what I get. but some of my airflow signals I couldn't get this ,the integrated signal was strange.I saved the data with the same procedure. you can find data as attachment. What would be the reason for this?

Re: calculating lung volume from airflow signal

burcu — Sat, 22 Jan 2005 23:17:01 GMT

You can find the strange integrated signal in the attachment

Re: calculating lung volume from airflow signal

chilly_charly — Sun, 23 Jan 2005 02:17:13 GMT

Hi Burcu !
Still stuck with peaks ? 😉
There is nothing strange in your integration signal : You are integrating over the whole signal range, and your data present a small offset. That gives a continuously increasing result.
Remember : the integral of a constant is a straight line.
And the integral of a sine function is a cosine function.
This second statement explains why you do not obtain the lung volume : you are integrating over the whole signal, instead of integrating on only a breath duration!
I suppose that your signal is the air flow rate (BTW, what is the signal unit ? ml/s, l/min ?). You are apparently recording both positive and negative air flow : air entering and leaving the lungs. Of course, the sum of the two operations should be near zero, since respiration produces an amount of CO2 (as volume) nearly equal to the consumed O2. Otherwise the lungs would collapse (out>in) or explode (in>out)!
What you have to do is to detect the instants when the air flow crosses the zero value (ie going from breath in to breathe out, or the reverse), and integrate the signal only between these two instants. You will get result which sign will depend on the breath direction.
I'm sure that with Randall help's you will rapidly find the solution now.

CC

Re: calculating lung volume from airflow signal

rpursley8 — Sun, 23 Jan 2005 02:34:36 GMT

For each set of data, try doing the following

1. Truncate any part of the data that is not actually representative of the airflow measurements
2. Find the average value of the remaining data and subtract that from your signal
3. Take the running integral as before

Your signal should be the airflow signal

Re: calculating lung volume from airflow signal

chilly_charly — Sun, 23 Jan 2005 02:43:50 GMT

Just a correction to my previous post :
there is no real need to find the zero crossing point : the lung volume is simply the positive and negative maxs of the signal integral over several breaths. Sorry to have missed that !
The only thing that remains to be done is to remove the DC component when present, as in the last Burcu's example...

CC

Re: calculating lung volume from airflow signal

burcu — Sun, 23 Jan 2005 21:50:00 GMT

Hi,
My signal is airflow and unit is liters/second.I'm trying to calculate volume from this signal.I'm taking integral of this signal offline after saving airflow data.It is strange that I saved a data 1 as you can find as attachment and I can see a proper signal when I take the integral of it.

Re: calculating lung volume from airflow signal

burcu — Sun, 23 Jan 2005 21:52:52 GMT

However, Ican't see the proper signal in my saved data called 2 as you can find in the attachment. Isaved these two data in the same ondiitons with the same vi. Why can I see with data 1 a proper volume signal while I can't see with data 2?

Re: calculating lung volume from airflow signal

burcu — Sun, 23 Jan 2005 21:55:53 GMT

I'm sending the vi as attached.How should I modify this in order to see volume properly.

Re: calculating lung volume from airflow signal

rpursley8 — Mon, 24 Jan 2005 01:54:47 GMT

If you look at the 2.txt data you will see that there is a DC offset across your data of around 0,12. When you subtract the DC offset from the data, you get a good looking plot. There is a function called 'AC&DC Estimator' that will give you the number to subtract from your data. Add this to your program before you take the integral. Also, it wouldn't hurt to apply a lowpass filter as with your ECG data, you seem to have 50/60 Hz riding on your signal.

As for getting your data, you really need to start from a known state. If I were you, I would have your subject take as big a deep breath as he can and hold it until you start the acquisition and then exhale as much as he/she can. Have the subject repeat two or three more times (in the same acquisition) and then breathe in whatever way you want. The first few will give you a max/min reference for (assuming the exhale is the minimum volume or zero reference point) the rest of your analysis.

Re: calculating lung volume from airflow signal

burcu — Tue, 25 Jan 2005 06:53:36 GMT

Hi,
I used AC&DC estimator and it worked. Thanks for your help.

Me again with new subject...

LW-s — Sun, 12 Jun 2005 15:20:12 GMT

Hello Charlie,

I am trying to acquire pressure signals from the parallel port in order to calculate flow and volume waveforms and some time data related to flow waveform.
but i have some problems;

1- i need to automaticly measure and digitally display the inspiration time and expiration time which are related to flow waveform; inspiration time is the total duration of flow travilling on the positive side and expiration time is the duration of flow travelling on the negative side.

2- my sample rate is 200 Hz in the waveform graph. should i use and array to combine x and y values and should i use 0.005 value for x-axis.

3- when my pressure signal is zero at the input, i see 24 value on the inport at labview. how can i deal with it and pull the value to zero for zero input value.
other vaules of input are accurate. when i send 255, i see 255 on inport function.

i am attaching an example flow graph, and i will send a screenshot of my block diagram at my next message.

thanks for your help.

Burcu

Block diagram

LW-s — Sun, 12 Jun 2005 15:23:18 GMT

i am attaching my block diagram`s screen shot...

flow

LW-s — Sun, 12 Jun 2005 15:24:53 GMT

I am attaching an example flow waveform graph...