GAS EXCHANGE AND ENERGY COST OF RUNNING IN ASTHMATIC CHILDREN

Abstract

Little information is available on the ventilatory and gas exchange changes occurring during exercise in children with exercise induced asthma (EIA).The purpose of this study is to evaluate the pattern of gas exchange during exercise and the energy cost of running in asthmatic children with and without premedication. 12 children (7.1-15.5 years) with a history of mild-moderate bronchial asthma and EIA performed two maximal exercise tests on treadmill on separate days: 1) test A = without premedication; 2) test B = disodium cromoglycate (DSCG) (40 mg) was inhaled 30 min before exercise. After a 3-min resting evaluation, the sceed of the belt was set at 6.5 km/h and the inclination was increased stepwise by 2%. every minute until exhaustion. Oxygen uptake (VO2). carbon dioxide outoufc (VCO2), ventilation (VE), respiratory rate (RR) and heart rate (HR) were measured every 4 seconds. The nertent post-exercise fall in FEV1 was calculated. The energy cost (CE) of running, defined as the amount of energy (above pre-exercise resting} spent oer unit distance, was calculated as a function of the incline of the belt at each minute of exercise. None of the children was limited by dyspnoea during the run; the postexercise fall in FEV1 after test A was ≥20% for each child, the mean fall being 32.8±11.6% in comparison with 12.6±8.9% after test 8 to (p<0.001). The run time increased from 8.0±2.6 min in test A to 9.1±2.1 min in test S (p<0.01). Baseline VO2 was not different between the two tests, VO2max decreased from 43,9±7.7 ml/min/kg in test A to 37,7±6.0 lower in test B (p<0.01). VE (l/min) and CE of running (ml 027/kg/m) were significantly lower in test B from the second to the last minute of exercise. In conclusion children with post-exercise bronchcsoasm snow which level of ventilation which causes secondary increased O2 cost of oreathinc during exercise, when they are asymptomatic. Our results, that surprisingly demonstrate a decrease of VO2max with premedication, suggest that the energy cost of running is a is more reliable parameter than tne VO2max in the evaluation of exercise response in diseases, such as asthma, in which high values of oxygen uptake are not coupled to high values of external work.