AIR TRAPPING AND CARDIOPULMONARY EXERCISE TESTING IN PATIENTS WITH MILD-TO-MODERATE BRONCHIAL OBSTRUCTION - CLINICAL ROLE OF TRAPPED GAS MEASUREMENTS

In 14 patients with obstructive airways disease (7 atopic asthmatics, 7 COPD pts with stable disease, FEV1 < 65 % pred., 11 m, 3 f, age 50.9 +/- 172 y) the effect of a beta mimetic agent on physical performance was studied. Protocol: Inhalation of 2.5 ml normal saline (P) or salb utamol 0.1 % (S) in double-blind random order on 2 successive days. Sp irometry, body-plethysmography, single-breath helium dilution at rest. Spiroergometry with incremental workload to tolerance. The volume of trapped gas (D) was derived from: TLC Body - TLC Helium Single Breath. Results: Base line values revealed mild to moderate airways obstructi on (FEV1 2.04 +/- 0.81 L, FEV1/VC 60.2 +/- 8.5 %). Subsequent to inhal ing S FEV1 increased significant by 20 % to 2.38 +/- 0.87 L. There was a concomitant substantial improvement of VC (3.37 +/- 1.09 L to 3.60 +/- 0.93 L). Rs declined sign. (2.37 +/- 1.43 to 1.69 +/- 0.8 kPs), a nd so did D (1.15 +/- 0.73 L to 0.55 +/- 0.89 L = -20 % from base line ). Despite clear-cut bronchodilation exercise performance did not impr ove in response to S (114.6 +/- 49.3 vs 112.5 +/- 50.0 Watt max, ns). Base line max. VO2 (19.78 +/- 6.36 ml/min/kg) and VO2 at anaerobic thr eshold (13.29 +/- 3.21 ml/min/kg) suggested only minimal impairment of physical performance. S induced a small but significant decrease in m ax. VO2 (19.78 +/- 6.36 to 18.43 +/- 6.27 ml/min/kg, p < 0.025). Gas e xchange (derived from AaDO(2)) was impaired at rest (30.18 +/- 10.4 mm Hg) and during exercise (28.07 +/- 13.03 mmHg). Wasted ventilation (VD /VT) was normal (0.22 +/- 0.07 r; 0.21 +/- 0.07 ex). Resting values de clined substantially following administration of S (0.22 +/- 0.07 to 0 .17 +/- 0.07). No correlation was established between AaDO(2) and VDA/ T on one hand and FEV1 on the other. The S-induced fall of D was not c orrelated with changes in maximal performance (r = -0.28). VD/VT prior to and after bronchodilation was only weakly related to the correspon ding D (r = 0.32/r = 0.44, n = 12, ns). Conclusions: Inhalation of 2.5 mg of salbutamol does not improve exercise performance in pts with mi ld to moderate airflow limitation. Changes in trapped gas volume and p hysical performance are not interrelated in pts under study. Conflicti ng results (1-4) are supposed to be due to different design and patien t selection. There is no definite proof so far that the volume of trap ped gas may be more intimately associated with wasted ventilation in o bstructive pts than are conventional parameters of airflow limitation. However, considering the still small number of patients, results have to be weighed with caution.