Anthropometric characteristics, pulmonary function and blood gases data for normal subjects and the three functional classes of patients are presented in Table 1. Group mean values for age, weight and height were comparable with each group. In patients, the hemoglobin concentration was within normal range (160±20 g/L for men in the laboratory); this measurement was not obtained in normal subjects. In patients, deterioration in functional status from class B to D was accompanied by a progressive reduction in FEV1 and PaO2, and by the development of resting hypercapnia.
La/VO2 relationship in normal subjects and COPD: The La/VO2 relationship was fitted by an exponential function in each normal subject and in 46 of 54 COPD patients. The exponential curve fitting was not performed in patients with extremely poor exercise tolerance (class D patients) because only two or three experimental data points could be obtained in these individuals. In normal subjects and COPD patients, the experimental data were well fitted by the exponential function with r ranging from 0.95 to 0.99. Parameter a was similar for the two groups averaging -0.89±0.24 and -1.00±0.00 in patients and normal subjects, respectively.
Table 1. Subjects’ character i st i cs in relat i on to funct i onal class
|Class D (n=8)||Class C (n=31)||Class B (n=15)||Normal subjects (n=10)|
|FEV1 (% predicted)||28±8*||33±7*||48±14t||104±8t|
|FVC (% predicted)||52±4*||62±11§||68±13§||93±8t|
|TLC (% predicted)||134±17**||127±24**||121±18**||95±10t|
|DLCO (% predicted)||62±22**||68±22**||85±20**||107±11t|
|PO2 (mm Hg)||73±13*||77±8*||84±10fl||95±131|
|Oxygen saturation (%)||95±3*||96±2**||97±2tt||98±1tJ|
|PCO2 (mm Hg)||50±6t||43±5tt||41±4tt||39±4tt|
All values are mean ± SD. *P<0.05 versus class D or C and P<0.001 versus any other group; fP<0.005 versus any other group; *P<0.05 versus class B and normal subjects; §P<0.05 versus class D and normal subjects; ^P<0.05 versus any other group; **P<0.05 versus normal subjects; ffP<0.05 versus class D; **P<0.005 versus class D and C. DLCO; FEV1 Forced expiratory volume in 1 s; FVC Forced vital capacity; TLC Total lung capacity
PCO2 (mm Hg)