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Respiration calibration


Calibration with fixed volume bags


The calibration analysis allows ANSLAB to translate a subject’s respiration band movements into calibrated respiration variables such as tidal volume or inspiratory flow rate.  During an experiment, all subjects need to perform a calibration procedure conisting of repeated (e.g., 8) inhalations and exhalations of a standardized volume (e.g., 750 ml).  ANSLAB matches the change in respiration bands with the known volume and uses this information to calculate lung volume throughout the experiment. Your job during the calibration analysis is to locate these breath cycles and select those which most consistently approximate the bag volume.  After telling ANSLAB which breaths to use, you may proceed to editing respiration data.


Select "Find breath maxima and minima automatically"....


----- Choose method for finding extremes: -----

 

      1) Find breath maxima and minima automatically

      2) Manual setting of maxima and minima



Select "Find maxima with default thresholds" ....



----- Choose threshold method: -----
 
      1) Find maxima with default thresholds
      2) Change default thresholds
      3) Quit



A window will open, displaying thoracic (yellow) and abdominal (magenta) breathing cycles. Your goal now is to exclude all non-calibration cycles, and all “bad” calibration cycles. In the optimal case, you keep 6-8 breathing cycles. But it is better to leave out breaths that are not done correctly than to have the full set. Therefore: When in doubt, exclude cycles. Minimally, you should have 3 good breaths altogether. “Good” are several regular breaths that are consistent and will probably add up to the same amplitude.

This window shows one good calibration set:

 



You can zoom into the signal by drawing a box with the mouse, and unzoom with a right mouseclick.

Now, you can step-by-step exclude all the “bad” cycles by typing in the corresponding numbers:
     
Take out cycle no. [e.g., 3, or: 1-12; <enter>=end] ==>  1
Take out cycle no. [e.g., 3, or: 1-12; <enter>=end] ==>  5






When you are done, you just hit <enter>:


 Take out cycle no. [e.g., 3, or: 1-12; <enter>=end] ==> <Enter>


 Then [select "Quit"]
     


Next, you are asked to decide how many channels were “OK”....


----- Specify qualitiy of thorax and abdomen: -----
 
      1) Both channels ok
      2) Only thorax ok
      3) Only abdomen ok


Depending on your decision select "Both channels o.k.” “only thorax o.k.” or “only abdomen o.k.” Most of the time you will be able to say “both channels o.k.,” but sometimes you might only be able to find 3 regular breaths for thorax, and have to say “only thorax o.k.” This might be the case if the other signal is bad due to technical difficulties, e.g. frequent resets or a zero signal.

Then, two new windows will open that will show the voltage change of the breathing bands and their “beta weights” predicting lung volume (don’t worry too much about their meaning). This second window, “beta-weights”, can additionally help you exclude outliers, since an outlier will be seen as a peak in this display, which is outside the broken line. Normally, though, if you have thoroughly excluded breaths in the first step, you can just move on by hitting <enter>

 


Note: In this figure, all breaths fit within an acceptable deviation from 750 ml (or cubic centimeters, ccm).  Keep all.


In some cases, though, there might still be an outlier. Keep in mind that the scale on your left can show a rather large range (e.g. 0-2500 ccm), in which case a peak will be relevant, or a rather small range (e.g. 400-1100 ccm), in which case a peak will be less relevant. When you exclude an outlier by typing in the corresponding number, the beta weight (displayed above the window) will change. Only if they change a lot, the outlier was relevant, but a rule of thumb is: “when in doubt, exclude.”

When you are done with excluding outliers, hit <enter>

Take which breath out of equation? (<enter>=end, 99=start again) ==> <Enter>


Then select 'Last betas'...


---- Save which betas to be used in analysis of respiration: -----
 
      1) Last betas
      2) Other betas
      3) Do not save betas (can be changed manually in file tex.txt)



    
Special Cases
     
What Do I Do When Thorax and Abdomen Move in Opposite Directions? This is called ‘paradoxical breathing’ and it makes calibration difficult.  If you can find some cycles or breaths within cycles that are synchronous, use them; if not, select ‘only thorax o.k.’ option.

What If There is No Usable Respiration Calibration File? You can still salvage respiration data.  The easiest ‘fix’ is to manually enter estimated calibration coefficients into the [study]c.m file using Excel.  Estimate these coefficients by looking at the coefficients of subjects of same age and sex.  As a constraint in the regression model estimating the beta weights, thoracic coefficients are set to twice the value of abdominal coefficients (this is supported by a publication that showed that this provides the most consistently accurate calibrations). Now check the baseline respiration data in ANSLAB.  Have most breaths been correctly detected?  You can modify the coefficients you entered if anything about the breaths or minute ventilation seems unreasonable.  For example, decreasing the coefficients by a factor of 3 will decrease baseline minute ventilation by about a factor of 3. Typical baseline minute volumes are in the order of 4-8 liters per minute. Using estimated coefficients will certainly affect the accuracy of respiratory volume variables (tidal volume, minute ventilation, inspiratory flow rate), but all timing related variables will be correct. The volume inaccuracy will be systematic within the subject. Since the error is multiplicative rather than additive, change scores for within subject analyses should be percent change scores.