Hemodynamic, not ventilatory, inefficiency is associated with high VE/VCO2 slope in repaired, noncyanotic congenital heart disease

Abstract Background A high slope of the ventilation vs. carbon dioxide relationship (VE/VCO 2 slope) during incremental exercise has been reported in several congenital heart disease (CHD) types, but it is not clear whether the main cause of high VE/VCO 2 slope is excessive ventilation or reduced perfusion. Methods We studied 169 adolescent and adult patients with repaired, noncyanotic CHD, divided into 2 groups according to VE/VCO 2 slope %predicted values (≤120 and >120), and 15 age- and sex-matched normals. VCO 2 /VE max and VO 2 /VE max were considered proxies of the perfusion/ventilation relationship, with VCO 2 and VO 2 as indirect descriptors of cardiac output. Results VCO 2 /VE max was significantly and inversely related to VE/VCO 2 slope (r=−0.73, p 120 (39.6±7.7, 36.1±5.3 and 28.5±4.1, respectively, p 2 at VCO 2 /VE max was higher in normals and ≤120 than in >120 (1701±474, 1480±492 and 1169±388ml/min, respectively, p 2 /VE max showed no changes (43±8, 41±12, 41±11 and 41±9l/min, respectively, p=0.82) between groups. Thus, differences in VCO 2 /VE max and VE/VCO 2 slope between groups were due mostly to changes in VCO 2 , i.e. in cardiac output, rather than ventilation. The same behavior was observed for VO 2 /VE max. Conclusions A high VE/VCO 2 slope observed in patients with repaired, noncyanotic CHD seems not to depend on excessive ventilation but on hypoperfusion due to impaired cardiac output response to incremental exercise. This finding should focus researchers' attention mainly on the heart when addressing exercise pathophysiology of this patient population.