When LP 2.0 was released, the original Respiration Monitor Belt files were changed from mmHg to kPa. The algorithm for rate calculation was not modified at the time. Any respiration wave that doesn't exceed 3 kPa is thrown out by the algorithm. The experiment files for Experiment 26 in BWC and the default experiment file in Probes and Sensors have been modified.
This problem does not exist in Logger Pro 3.
Download the latest version of Logger Pro 2 from the Vernier website to remedy this problem: http://www.vernier.com/tech/lpupdates.html
In LP 2.1.1 in order to measure heart rate and respiration rate (with either a Gas Pressure Sensor or a Biology Gas Pressure Sensor) at the same time you will need to adjust the "Respiration and Heart Rate" experiment file. To do this
(a) Open the experiment file;
(b) Go to Data/Modify Column/Rate;
(c) Select the 3 at the end of the rate formula and change it to 0.5.
(d) Click OK, and save the file.