Guidelines for obtaining better respiration data when using a respiration belt transducer
Avoid noise in the first place
Properly use the Respiration Belt Transducer
A good signal requires proper attachment of the belt to the transducer and the transducer to the subject.
Respiration Belt Attachment
Respiration Transducer placement
Identify noise in the respiration data
It is not always trivial to determine whether an apparent abnormality in the respiration record is physiological in nature or not. A synchronized video recording of the subject can help in the identification of artifacts like subject movement, talking (see the AcqKnowledge software guide for information on recording video with AcqKnowledge). The experimenter could also manually enter markers in the data during the experiment whenever the subject moves, talks, etc. (See the section on Markers in the AcqKnowledge software guide).
There are several potential sources of noise for respiration recordings. This is how normal data and noisy data can look (RSP100C at gain 10, HP at 0.05 Hz and DC, LP at 1 Hz; respiration sensor placement over the abdomen):
The respiration data does not need to be sampled any faster than 50 samples per second. To make the filter transformations less computationally intensive resample the respiration waveform to 50 samples per second (if the sample rate is currently higher) by going to Transform > Resample.
Apply a Bandpass FIR filter between 0.05 Hz and 1 Hz. Go to Transform > Digital filters > FIR > Bandpass and enter 0.05 for the low frequency, 1 for the high frequency and 4000 for coefficients (assuming a sample rate of 50 Hz).
The signal will be a little cleaner and centered around 0. (Display >Autoscale waveform will bring the signal into view)
Keep the respiration rate calculation as it is.
PROS: Less work intensive and if the noise is a small fraction of the data it should average out
CONS: Reducing the statistical power of your experiment or even distorting the results; need to determine how much noise is acceptable
Use Connect Endpoints to interpolate over the problematic section.
PROS: Respiration is a slow signal and this solution will be acceptable over short periods of noise
CONS: Reducing the statistical power of your experiment or even distorting the results; need to determine how much interpolation is acceptable
Example: rate artifact before and after connect endpoints:
PROS: Ideal if the respiration cycles can still be visually identifiedCONS: Relies on human judgment to identify respiration cycles and itroduces subjectivity