Measuring ease of breathing in young patients with cystic fibrosis

Our objective was to compare two new objective measures of ease of breathing with the visual analog scale (VAS). Twenty-eight patients with CF, 7-34 years old (FEV(1) 25-114% of predicted), enrolled. Ease of breathing was evaluated by a standard 10-cm VAS, maximum phonation (time, in seconds, to sustain the syllable "Ahh") using a single breath, and counting in a single breath at one number per second (Count) at rest, following 3 min of stepping exercise at 15 steps per minute (STEP15), and 3 min at 30 steps per minute (STEP30). Heart rate (HR) and oxyhemoglobin saturation (SaO(2)) were measured.HR and VAS increased significantly, and SaO(2), phonation, and Count decreased significantly from rest to STEP15 and STEP30. Phonation time correlated significantly (and inversely) with HR after exercise. Phonation time was positively correlated with SaO(2) at rest and after STEP30. Counts at rest and after STEP30 were significantly related to SaO(2). VAS showed no relationship to heart rate at rest or after exercise, but was related to SaO(2) at the end of STEP30. Test-retest reliability for three trials of phonation was 0.92, and for the five trials of counting was 0.93. Correlation coefficients for maximum phonation at rest, STEP15, and STEP30 on 2 separate days were 0.61, 0.94, and 0.91, respectively. Correlation coefficients for Count at rest, STEP15, and STEP30 on 2 separate days were 0.96, 0.94, and 0.94, respectively. Correlation coefficients for VAS at rest, STEP15, and STEP30 on 2 separate days were 0.25, 0.89, and 0.97, respectively. Thus both the maximum phonation and Count have good test-retest reliability within one session, and across 2 separate days, for both rest and exercise conditions. In conclusion, maximum phonation and Count are valid and reliable measures of ease of breathing; they reflect increasing work loads and show stronger correlations with heart rate and SaO(2) than does VAS. These measures could be an important tool for clinical research and patient care.