FUNCTIONAL OUTCOME OF PATIENTS WITH CHRONIC OBSTRUCTIVE PULMONARY-DISEASE AND EXERCISE HYPERCAPNIA

Chronic hypercapnia is associated with a poor prognosis in chronic obs tructive pulmonary disease (COPD), Some patients are normocapnic at re st but retain CO2 during exercise, The significance of this abnormalit y on the course of the disease is unknown. Sixteen stable COPD patient s (13 males and 3 females, aged 60 +/- 5 yrs, mean +/- SD) who had pre viously undergone pulmonary function tests and progressive exercise te sting with arterial blood sampling at rest and maximal capacity, enter ed the study, At first evaluation (E1), subjects were normocapnic at r est (arterial carbon dioxide tension (Pa,CO2): 4.9-5.7 kPa, (37-43 mmH g)) and all presented exercise-induced hypercapnia (end-exercise Pa,CO 2 >5.7 kPa (43 mmHg) with a minimal 0.5 kPa (4 mmHg) increase from res ting value), The subjects were re-evaluated 24-54 months later (34 +/- 8 months) (second evaluation (E2)). At E2, forced expiratory volume i n one second (FEV(1)) had decreased from 42 +/- 13 to 38 +/- 15% of pr edicted values, and mean resting Pa,CO2 had increased from 5.2 +/- 0.3 to 5.7 + 0.4 kPa, Maximal exercise capacity (Wmax) decreased between E1 and E2 from 76 +/- 30 to 56 +/- 22 W. Even if Wmax was lower at E2, end-exercise Pa,CO2 was higher than at E1 (6.6 +/- 0.8 vs 6.4 +/- 0.5 kPa), At E2, eight subjects presented resting hypercapnia (group H), whilst the others remained normocapnic (Group N), Group H subjects had higher Pa,CO2, at Wmax than Group N and lower Wmax than Group N at E2 , Group H and N were not significantly different for physiological dea d space/tidal volume ratio (VD/VT), FEV(1), lung volumes and transfer factor of the lungs for carbon monoxide (TL,CO), both at E1 and E2. In half of the patients studied, exercise hypercapnia was a step in the progression of COPD towards resting hypercapnia, and was associated wi th severe exercise limitation, During exercise, patients who responded to a deterioration in their lung function by increasing minute ventil ation remained normocapnic at rest, whilst those who did not increase their ventilation developed chronic hypercapnia at rest during the 2-4 year follow-up period.