Below are some limitations of this procedure, according to the international scientific community:
Overestimation of TGV in subjects with severe obstruction or induced bronchospasm unless slow ‘panting’ speed
(ie, approximately 1 cycle/s) is maintained.
Erroneous measurement of TGV, Raw, or sGaw due to improper panting techn ique. Excessive pressure
fluctuations or signal drift during panting may invalidate TGV, Raw, or sGaw.
Non-panting measurements have been suggested for use in children or others who have difficulty mastering the
panting maneuver. Non-panting maneuvers in plethysmographs with built-in thermal leaks may invalidate TGV or
Raw measurements.
Computer-determined slopes of either TGV or Raw tangents may be inaccurate. All slopes should be visually
inspected and adjusted according to an established laboratory procedure.
Excessive abdominal gas or panting techniques that employ accessory muscles may increase the measured TGV,
due to compression effects.
Plethysmography is a complex test. Careful calibration of multiple transducers is required. Attention to frequency
response, thermal stability, and leaks is necessary.
Choice and application of reference values affect interpretation. Reference values for TGV using
plethysmographically determined lung volumes are not widely available.
Make a tentative selection from whatever published reference values are available. The characteristics of the
healthy reference population should match the study group with respect to age, body size, gender, and race. The
equipment, techniques, and measurement conditions should be similar.
Following selection of seemingly appropriate reference values, compare measurements obtained from a
representative sample of healthy individuals (10-20 subjects, over an appropriate age range) to the predicted
values obtained from the selected reference values. If an appreciable number of the sample fall outside of the
normal range, more appropriate reference values should be sought.