This study was designed to investigate the reproducibility and clinical relevance of several lung function and exercise test indices in a sample of patients with stable severe chronic obstructive pulmonary disease (COPD). Twenty subjects (ages 67.8 +/- 2.0 years, forced expiratory volume in 1s, [FEV1] 39.7 +/- 2.8% predicted) receiving conventional medical therapy and pulmonary rehabilitation were tested 4 times at 1 month intervals. Testing procedures included lung function (inspiratory vital capacity [IVC], FEV1, plethysmographic functional residual capacity [FRC], specific conductance of the airways (sGaw), single breath transfer factor divided by the alveolar volume [TL/VA]); incremental, progressive, symptom-limited, cycle exercise (maximum work load [Wmax], maximum heart rate [HRmax], maximum ventilation [VEmax], maximum oxygen uptake [VO2max]); and 2 modes of submaximum exercise (12 min walking test [12 MWD] and endurance cycle test). The mean of the absolute value of the individual patient, session-to-session, variation was found to be 0.131 for FEV1, 102 ml/min for VO2max. The within-subject variability was the smallest for HRmax and IVC (mean intrasubject coefficient of variation, [CV intra] 5.0 and 6.5%) and the greatest for TL/VA, the work performed during the endurance cycle test (EW) and sGaw (CV intra 16.5, 19.4, and 22.7%), while it was reasonably low (8.1-10.2%) for all the other variables studied. Calculation of the F ratio of the intersubject variance to the residual (total minus intersubject) variance, interpreted as a signal-to-noise, ratio, yielded the following, in decreasing order: TL/VA, EW, VEmax, VO2max, IVC, FEV1, HRmax, Wmax, sGaw, 12 MWD, FRC. If we assume that a useful variable should combine a low within-subject variability (CV intra less than or equal to 10%) with a high signal-to-noise ratio, we conclude that, among all the variables studied, IVC, FEV1, VEmax, and VO2max are those with the greatest clinical potential for functional assessment in patients with COPD.

The aim of the study was to evaluate the relationship between several lung function indices and perceived dyspnoea during bronchoconstriction. Acute changes in lung function were induced by inhaled histamine followed by terbutaline, in 12 asthmatics and 12 subjects with chronic obstructive pulmonary disease (COPD). A bipolar visual analogue scale (VAS), allowing subjects to report either improvement or worsening when moving off from a 'nochange' midpoint, was used to rate shortness of breath. Large swings in ratings were seen in all asthmatics and in seven out of 12 COPD subjects (high perceivers). Using linear regression of VAS rating against parallel change in lung function, on a within-subject basis, the highest degree of correlation between dyspnoea and objective response was found to involve the change in specific inspiratory resistance (sRin) in the asthmatics. In the five low perceivers, the ability to discriminate an increase in airway obstruction, estimated as the VAS/change in lung function slope, was very poor. Using a stepwise multiple regression analysis, the sensation of dyspnoea was found to be significantly related to the FEV1 and the sRin in the asthmatics, to the inspiratory vital capacity and the maximal inspiratory flow at 50% FVC (MIF50) in the COPD subjects with high perception, and to the MIF50 in the COPD subjects with low perception.

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