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Respirometry menu
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If you are unfamiliar with the fundamentals of respirometry, you might want to read this page before diving into the rest of this section. .   Also, John Lighton's book, Measuring Metabolic Rates - A Manual for Scientists is an excellent reference.
Choose one of two computation modes: • Positive-going deflection: Changes in gas concentration are positive with respect to baseline (the default). • Negative-going deflection: Changes in gas concentration are negative with respect to baseline. This can be used if -- as in oxygen consumption -- gas exchange is measured as a depletion of gas concentration. Many users find positive-going deflections more intuitive, but the negative-going option is available if desired. • NO downstream scrubbing Switches respirometry mode to computing gas exchange without removal of water vapor and CO2 from analyzed gas, as described on this page.
Results are stored either in the source channel or optionally (if there are less than 40 channels) in a new channel. Gas calculations begin with flow rate source selection. Flowrate is entered from the file or by the user, or is obtained from a channel (i.e., recorded from a flow meter).
For VO2 and VCO2 , you need to specify: • whether incurrent CO2 is absorbed – note that this refers to gas entering the metabolism chamber, NOT to gas entering the analyzers. If you are using ‘standard’ air (where the CO2 concentration is about .04%), this option has little effect. • concentrations of O2 and CO2 in ambient gas (FiO2 and FiCO2; default 20.95% and 0.04%, respectively – note that the program expects these to be entered as percentages, not fractions).
For relative humidity sensors, you will also need to indicate operating temperature of the sensor (this is done later; see below). Channel selection: In the next window (below,left) you select the channel containing gas concentration data, and if you are obtaining flow from a channel, the flow rate channel: Flow configurations: Next you select a flow configuration ('Mode' 1, 2, etc.). This specifies the conversion equation to be used, based on where flow rate is measured (upstream or downstream of the animal chamber and gas sensor) and how (and if) the the gas stream is dehumidified and scrubbed of CO2.
Pick the configuration and mode closest to your own respirometry system. It's quite important to give LabAnalyst the right information about your flow arrangement. In some -- but not all -- cases, with 'normal' incurrent concentrations of CO2 and O2 (about 0.04% and 20.9%), different modes yield fairly similar results. However, in some cases, serious errors (20% or more) can result if the wrong equations are used (this is most problematic for VO2). Selecting the appropriate configuration is most critical if the sample gas from the animal chamber has large deflections from ambient concentrations of CO2 and O2. An important and easily avoidable error will result if the gas stream at the flow meter contains a significant (but unknown) fraction of water vapor. Therefore it's good practice to use DRY gas whenever possible -- and if you can't, be sure to compensate as described in the next section.
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