Constant volume respirometry

When using the MINIMUM VALUE...  and MAXIMUM VALUE... functions, a button labeled 'C.V.R.  data...' is available.  This stands for Cinstant Vplume Respirometry, and it opens a window that lets you set up the variables needed to compute O2 or CO2 exchange in a closed system.   In constant volume respirometry (or 'closed system' respirometry), the organism is placed in a sealed chamber, and over time its respiration changes the gas concentrations in the chamber.   You measure rates of gas exchange by determining gas concentrations (O2 and/or CO2 ) at the start and end of a period of measurement, and then using the cumulative difference in concentrations and the elapsed time to compute the average rate of change.

The most straightforward way to handle constant volume calculations with LabHelper and LabAnalyst is as follows:   First, collect samples of 'initial' and 'final' gas from the animal chamber(s) and inject them through a gas analyzer while continually recording the concentration (in %) with LabHelper.   Between injections, flush the analyzer with reference gas (or fluid). You should get a data file with a series of 'peaks', one for each injection of 'final' gas (or fluid).   Next, in LabAnalyst, use the baseline function to set the 'initial' values at zero.   The 'final' values now show the % change during the measurement period.  These peaks are what you analyze with the C.V.R. data... option.   For each peak, find the maximum deflection from baseline with the MAXUMUM VALUE option, and then switch to C.V.R. data....

Note that this option assumes that the data being analyzed are in units of % gas concentration and that baseline has already been corrected.   You need to specify the gas type, the chamber volume, the elapsed time, the chamber temperature, the barometric pressure, the initial relative humidity in the chamber (if the gas contains water vapor), the initial concentrations of O2 and CO2 (FiO2 and FiCO2), and the respiratory exchange ratio (RQ).  You also need to specify whether or not CO2 is absorbed prior to oxygen analysis ('excurrent CO2' buttons).  When done, click the 'Selection OK' button.

When C.V.R. data... is activated, the results window (example on the right) shows gas exchange rates in units of ml/min -- but note that only the mean value is computed as gas exchange (the SD, SE, etc.  are shown in their original units).  To switch off the C.V.R.  calculations, click the 'C.V.R.  data...' button.   Note that this is a “quick and dirty” CVR estimate; a more versatile CVR calculator is in the SPECIAL menu.


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