DYNAMICS OF RESPIRATORY GAS-EXCHANGE DURING EXERCISE AFTER CORRECTIONOF CONGENITAL HEART-DISEASE

In pediatric exercise testing, conventional measures of aerobic exerci se function such as maximal O-2 uptake or the ventilatory anaerobic th reshold (VAT) use only one value for the assessment of exercise capaci ty. We studied a more comprehensive approach to evaluate aerobic exerc ise function by analyzing the steepness of the slope of CO2 production (VCO2) vs. VO2 above the VAT (S3). This was calculated in 32 patients operated on for congenital heart disease [16 for transposition of the great arteries (TGA) and 16 for tetralogy of Fallot (TF)] and was com pared with 16 age-matched controls (nl). The results show that the rep roducibility of this new assessment method was excellent (coefficient of variation for S3: 8.6 %). S3 was significantly steeper (P < 0.05) i n the patients (1.31 +/- 0.22 for TGA and 1.28 +/- 0.16 for TF) compar ed with the nl (1.10 +/- 0.22). Also, the difference between S3 and th e slope of VCO2 vs. VO2 below the VAT was significantly higher in the patients (0.37 +/- 0.22 for TGA and 0.31 +/- 0.10 for TF) than in cont rols (0.22 +/- 0.06). The steeper slopes were associated with lower th an normal values for VAT and O-2 during exercise. It is concluded that the analysis of the steepness of the slope of CO2 is a sensitive, rep roducible, and objective approach to evaluate the integrative cardiopu lmonary response to exercise. It complements the assessment of a subno rmal VAT by reflecting the extent of anaerobic metabolism.