Measurement of Respiratory Sensation in Interstitial Lung Disease: Psychophysical Testing

5 Dec

Following the presentation of each respiratory load, the subject estimated the perceived magnitude of the sensation by pointing to a number on the Borg category scale. This scale lists phrases of increasing subjective intensity from zero, or “nothing at all,” to ten, or “maximal.” Each elastic load was presented in random order five times. The actual elastance applied on each loaded breath was calculated directly from the chart record by dividing the peak mouth pressure, measured by a differentia] pressure transducer (No. 4500, Vacu-metrics, Ventura, CA), by the corresponding tidal volume integrated from flow signals measured by a heated pneumotachograph (Hans Rudolph, Kansas City, MO). Signals were recorded on separate channels of a thermal recorder (model 1400, Honeywell, Inc, Newton, MA).

Prior to scaling added elastances, subjects estimated the heaviness of weights. While seated, the individual rested the elbow of his dominant upper extremity on a piece of foam placed on top of a table. With the forearm extended, the subject flexed his forearm to lift a handle attached to a weight inside an enclosed box. The subject lifted the handle until the box prevented further upward movement. The subject estimated the magnitude of the weight using the Borg category scale. Each of five different weights (2.3, 3.4, 4.8, 5.7, and 7.1 kg) was presented five times in random order.
The numerical exponent (n) describing the relationship between perceived magnitude (¥) and the physical stimulus (<!>) was determined using the psychophysical power function: ¥ = M>° where k is a constant. For heaviness of lifting weights, $ was the measured weight and ¥ was the Borg rating of heaviness. For magnitude estimation of added elastic loads, 4> was examined for the mouth pressure generated during the loaded breath, and ¥ was the perception of breathlessness on the Borg scale.