The objective measurement of breathlessness.

Both direct and indirect psychophysical methods can be used to measure breathlessness. With indirect methods, detection thresholds can be defined. Direct methods are easier to apply and give more information than indirect methods. Direct methods include interval (partition) and ratio scales, which are easy to apply; both have advantages and disadvantages. The selection of scale depends largely on the question addressed. For comparison across individuals or for the measurement of absolute magnitude (however imprecise), simple category scales are adequate and useful. Open magnitude scaling is best used to define the stimulus parameters influencing perceptual magnitude. Comparison across groups or individuals using exponents as an index of perceptual sensitivity should be interpreted with caution. Where possible, alternative methods should be used to validate differences found. The age-old bias against sensory measurement may be in part our inability to understand the sensory mechanisms and have little to do with the validity of the measurements.