Constant volume respirometry
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When using the BASIC STATS... (or AVERAGE), MINIMUM VALUE... or MAXIMUM VALUE... functions, a button labeled 'Use C.V.R.' is available. This stands for Cinstant Volume 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:
Note that this option assumes that the data being analyzed are in units of % gas concentration and that baseline has already been corrected. Click the 'Set C.V.R. Parameters...' button and, in the window that opens, specify gas type, chamber volume, elapsed time, chamber temperature, barometric pressure, 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 ('is excurrent CO2 absorbed?' button). When done, click the 'Store Data and Close' 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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