Reproducibility of the parameters of the on-transient cardiopulmonary responses during moderate exercise in patients with chronic obstructive pulmonary disease

To be clinically useful as indices reflective of altered physiological func tion consequent to interventions in patients with chronic obstructive pulmo nary disease (COPD). the time constant (tau) and steady-state amplitude of the kinetic responses for oxygen uptake ((V)over dotO(2)) carbon dioxide ou tput ((V)over dotCO(2)) ventilation ((V)over dot(E)) and heart rate (HR) ha ve to be appropriately differentiable and reproducible. We therefore assess ed the reproducibility of a and steady state amplitude values in 41 patient s with severe COPD [mean (SD)] [forced expiratory volume in 1 s=41 (7)% pre dicted], aged 64 (5) years. Of the total, 6 of the patients (15%) did not p roduce breath-by-breath data of sufficient quality to warrant kinetic analy sis. The remaining 35 patients completed two moderate-intensity 10 min squa re-wave exercise tests separated by 2 h, both before and after an endurance training programme. Tests were conducted on an electromagnetically-braked cycle ergometer at an exercise intensity corresponding to 80% of the estima ted lactate threshold (theta (La)) or 50% of peak oxygen uptake if theta (L a) was insufficiently differentiable. Breath-by-breath measurements of (V)o ver dotO(2), (V)over dotCO(2), (V)over dot(E) and HR were averaged into 10 s bins and the on-transient response kinetics were estimated using a mono-e xponential model. Analysing the pre-training and the post-training test 1 a nd test 2 comparisons together, the test 1 -test 2 differences were not sig nificantly different from 0 for either tau or A. The standard deviation of the test 1 -test 2 differences allowed us to define the magnitude of change that would reach statistical significance. For tau, this averaged some 8, 10, 11 and 8 s. for (V)over dotO(2), (V)over dotCO(2), (V)over dot(E) and H R, respectively, for a one-tailed paired-comparisons test (i.e. appropriate for assessing hypothesised improvements resulting from an intervention); f or a two-tailed comparison, the differences were approximately 2 s greater. The corresponding one-tailed values for A were 100 ml(.)min(-1), 95 ml(.)m in(-1). 2.5 1(.)min(-1) and 4 beats(.)min(-) 1, respectively; the two-taile d values were 10%-15% greater. We therefore conclude that both tau and A fo r moderate-intensity exercise can be reproducibly estimated in patients wit h COPD when the data set provides a sufficiently large amplitude of respons e and sufficiently low sample variability to allow appropriate parameter es timation.