From tommytroen at gmail.com  Mon Apr  3 21:16:26 2006
From: tommytroen at gmail.com (Tommy Troen)
Date: Tue, 4 Apr 2006 03:16:26 +0200
Subject: [Physionet-users] 
	physical units in percent from BVP sensor - WFDB: wrsamp gain?
Message-ID: <3e29ad4d0604031816h1e5c10d8ha3714bc8cc4a322b@mail.gmail.com>

Hi..




I have recorded physiological data using a BVP(Blood Volume Pulse)
sensor from Thought Technology. From this data I want to get the IBI
intervals and calculate the heart-rate. I have tried to create a
record and a header file using wrsamp. I specified the sample rate to
256 Hz but left the gain option blank as I didn't know what to use.
When conducting a peak detection using 'wqrs' proper N intervals
didn't occur before after 70000 or so samples.. I guess this has
something to do with the conversion to millivolts, because when
outputting the signal file important precsion was lost in the data
resulting in a great amount of samples with the same value..

The BVP values are a relative measure and are presented as percent and
not millivolts. This is a sample of the input file with the BVP data
passed on to 'wrsamp':

34,52
34,526
34,534
34,546
34,563
34,587
34,619
34,66
34,71
34,771
34,842
34,923
35,013
35,111
35,215
35,325
(The values range from roughly 30 - 40 in a normal state.)

So my question is: do anyone know how to figure out what gain to use
with different signal types? Or in particular what gain to use with
the BVP signal which are stored in percent?

I hope I managed to explain my problem..:)
Any help would be greatly appreciated!

Thanks

Tommy