Clinical Ratings of Dyspnea
A modification of the MRC scale, the OCD, and the BDI were used to quantify dyspnea in the patients. The modified MRC scale consists of five grades based on increasing levels of physical activity which provoke breathlessness. After the patients read the descriptive phrases, they selected the grade which best corresponded to their level of dyspnea. The OCD is a vertical line measuring 100 mm in length with daily activities positioned along the line according to increasing oxygen requirements. The patient was instructed “to mark the vertical line at a point above which you would become breathless.” The distance from the bottom of the vertical line to the patients mark was measured in millimeters. The BDI consists of five grades for each of three categories which provoke breathlessness: functional impairment; magnitude of task; and magnitude of effort. An observer was able to grade the degree of breathlessness based on the patients responses, and a baseline focal score was obtained by adding the grade for each of the three categories. The total time for each observer to complete the measurement of dyspnea using all three methods was less than five minutes per subject. All ratings were obtained without knowledge of results of pulmonary function testing.
The elastic breathing circuit consisted of four rigid, airtight glass containers of different volumes resulting in elastic loads of 20, 40, 80 and 160 cm H20/L. During presentation of the load, a container was connected to the inspiratory side of the breathing circuit by plastic tubing 2 cm in diameter; otherwise, it was vented to atmosphere. The resistance of the unloaded circuit was less than 1 cm HtO/L/s.
Initially, the subject sat comfortably in a dental chair and breathed through a mouthpiece connected to a two-way valve for 5 min. Thereafter, an elastic load was manually added to the circuit for a single inspiration approximately every 30 s. Prior to testing, each subject was given the following instructions:
You will breathe through the device before you. On a signal, an adjustment will be made making it harder to take your next breath. After just one breath, you will breathe normally. A series of these harder than normal breaths will be presented, each separated by approximately ten normal breaths. Immediately after each of these breaths, you will be asked to pick a number from the 0 to 10 scale. Please choose the number which most closely matches the difficulty of that breath (breathlessness).