| Minimum, maximum, level
Allow you to enter an interval (in seconds) and LabAnalyst will search within the selected block for either the highest or lowest continuous average over that interval, or the most level or most variable region within the block. In this example, the scan interval (86,400 seconds) is an entire day.
Activating the 'reuse this interval' button in the interval selection window will bypass the interval selection routine during subsequent uses of these analyses (such as when using the AUTOREPEAT option for new blocks).
You can restrict the analysis to specific ranges of data using the 'Exclude if' options. In the example, data with values less than 0.5 or greater than 21.12 are ignored during calculations.
For the MOST LEVEL option, the 'most level' region is the interval in which the sum of absolute differences from the interval mean (i.e., the sum of Xi - meanX, or point-to-point variance) is lowest. Note that this is not necessarily the interval with the lowest slope, although this usually turns out to be the case.
For the MOST VARIABLE option, you can select to search either for the region with maximum overall slope or the region with maximum point-to-point variance.
When your interval selection is complete, click the 'interval OK' button and the program will find the appropriate interval and display the results in the next window, shown below.
After calculations, the maximal, minimal, or most level area is shown as a color-inverted rectangle on the block window.
As for BASIC STATS, you can switch to other channels, but in the default mode the interval boundaries remain constant -- i.e., the same beginning and ending points as on the initially scanned channel are used for other channels. This sounds confusing but it allows you to scan for the period of, say, lowest VO2 and then get the temperature, CO2, etc. for that specific period.
Alternately, you can activate the 'rescan new channels' button to force a re-scan of each new channel selected.
Also as for BASIC STATS, you can see the channel labels if you 'float' the cursor over these buttons.
Two other considerations:
When using the MINIMUM VALUE... and MAXIMUM VALUE... functions, a button labeled 'C.V.R. data...' is available. This stands for Constant 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: 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.
You can avoid using interpolated data in these operations if you select the 'Avoid interpolated data' option in the ANALYSIS UTILITIES submenu (bottom of the ANALYSIS menu).