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Clinical relevance of constant power exercise duration changes in COPD

¹ Servicio de Neumología, Hospital General Universitario Gregorio Marañón, ² Fundación Jiménez Díaz, ⁴ Hospital Virgen de la Torre, CIBER Enfermedades Respiratorias (CIBERES), Madrid, Spain. ³ Los Angeles BioMedical Research Institute at Harbor-UCLA Medical Center, Torrance, CA, USA.

CORRESPONDENCE: L. Puente-Maestu, Hospital General Universitario, Gregorio Marañón, Servicio de Neumología, c/ Doctor Ezquerdo 46, 28007 Madrid, Spain. E-mail: lpuente.hgugm{at}salud.madrid.org

Keywords: Chronic respiratory questionnaire, clinically relevant changes, constant exercise test reliability

Received: May 24, 2008
Accepted February 17, 2009

The endurance time during constant high work-rate exercise (t_LIM) is used to assess exercise capacity in patients with chronic obstructive pulmonary disease and as an outcome measure for pulmonary rehabilitation. Our study was designed to establish the minimum clinically important difference for the t_LIM.

t_LIM was measured in 105 patients (86 males) before and after an 8-week outpatient pulmonary rehabilitation programme. Subjects were asked to identify, from a five-point Likert scale, the perceived change in their exercise performance immediately upon completion of the exercise tests. The scale ranged from "better" to "worse".

The mean±SD age was 64±5 yrs, forced expiratory volume in 1 s (FEV₁) 47±10% and FEV₁/forced vital capacity 54.7±16.3%. Baseline t_LIM at 75% of the peak work rate was 397±184 s, which increased by 62±63% after rehabilitation. In subjects who felt their exercise tolerance was "slightly better", the mean improvement was 34% in the relative improvement over the baseline value (95% CI 29–39)% or 101 (86–116) s compared with 121 (109–134)% in those who reported that their exercise tolerance was "better" and 8 (2–14)% in those who felt their exercise tolerance was "about the same".

Minimum clinically important improvement for t_LIM averaged 33% of baseline. Patients were able to distinguish at least one further additional level of benefit at 120% of baseline.