Abnormal dynamic cardiorespiratory responses to exercise in pediatric patients after Fontan procedure

Objectives. Novel protocols were used to focus on dynamic cardiorespiratory function during submaximal exercise and on the recovery from 1-min pulses of exercise in children who had undergone Fontan corrections for single-vent-ride lesions, Background. Particularly in children, maximal oxygen uptake ((V) over dotO(2)max), which is commonly used to assess the functional capability of patients after the Fontan procedure, is highly effort dependent and not physiologic and leads to uncomfortable metabolic and cardiorespiratory stress, Alternative approaches include the measurement of dynamic responses during progressive exercise and recovery after short. bursts of exercise, These strategies yield mechanistic insight into cardiorespiratory impairment and can be used to gauge limitations in daily life activity, Methods. Sixteen patients (mean [+/-SD] age 12.2 +/- 2.4 years; 9 boys) and 10 age-matched control subjects (mean age 12.2 +/- 2.4 years; 6 boys) performed two separate cycle ergometer tests in which gas exchange was measured on a breath by breath basis: 1) Progressive exercise was used to determine the dynamic relation among (V) over dotO(2), carbon dioxide production ((V) over dotCO(2)), ventilation ((V) over dotE), heart rate (HR) and work rate (WR). 2) A 1-min constant WR test was used to determine the recovery time for gas exchange and HR. Results. Peak (V) over dotO(2) and anaerobic threshold were reduced in patients who underwent the Fontan procedure compared with control subjects by 57% and 52%, respectively (p < 0.001), Dynamic relations during progressive exercise-Delta(V) over dotO(2)/Delta HR and Delta(V) over dot O-2/Delta WR-were decreased (p < 0.001) and Delta(V) over dotE/Delta over dotCO(2) , was increased (p < 0.005) in the Fontan group patients, Recovery times for HR and (V) over dotO(2) were prolonged in the Fontan group patients by 154% and 69%, respectively (p < 0.01), Conclusions. The results demonstrate that submaximal gas exchange responses to progressive exercise and recovery times after brief high intensity exercise are abnormal in patients after the Fontan procedure, These observations complement the findings of reduced (V) over dot(2)max observed here and by others, We speculate that the mechanisms for these responses are related to 1) a pervasive reduction in stroke volume for both low and high intensity exercise, 2) an abnormal linkage of ventilation to tissue carbon dioxide production, and 3) increased dependence on anaerobic metabolism in skeletal muscles, The prolonged recovery of HR and (V) over dotO(2), provides a possible mechanism for reduced physical activity. (C) 1998 by the American College of Cardiology.