ABNORMAL DYNAMIC CARDIORESPIRATORY RESPONSES TO EXERCISE IN PEDIATRIC-PATIENTS AFTER FONTAN PROCEDURE

Objectives. Novel protocols were used to focus on dynamic cardiorespir atory function during submaximal exercise and on the recovery from 1-m in pulses of exercise in children who had undergone Fontan corrections for single-vent-ride lesions, Background. Particularly in children, m aximal oxygen uptake ((V) over dotO(2)max), which is commonly used to assess the functional capability of patients after the Fontan procedur e, is highly effort dependent and not physiologic and leads to uncomfo rtable metabolic and cardiorespiratory stress, Alternative approaches include the measurement of dynamic responses during progressive exerci se and recovery after short. bursts of exercise, These strategies yiel d mechanistic insight into cardiorespiratory impairment and can be use d to gauge limitations in daily life activity, Methods. Sixteen patien ts (mean [+/-SD] age 12.2 +/- 2.4 years; 9 boys) and 10 age-matched co ntrol subjects (mean age 12.2 +/- 2.4 years; 6 boys) performed two sep arate cycle ergometer tests in which gas exchange was measured on a br eath by breath basis: 1) Progressive exercise was used to determine th e dynamic relation among (V) over dotO(2), carbon dioxide production ( (V) over dotCO(2)), ventilation ((V) over dotE), heart rate (HR) and w ork rate (WR). 2) A 1-min constant WR test was used to determine the r ecovery time for gas exchange and HR. Results. Peak (V) over dotO(2) a nd anaerobic threshold were reduced in patients who underwent the Font an procedure compared with control subjects by 57% and 52%, respective ly (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 decreas ed (p < 0.001) and Delta(V) over dotE/Delta over dotCO(2) , was increa sed (p < 0.005) in the Fontan group patients, Recovery times for HR an d (V) over dotO(2) were prolonged in the Fontan group patients by 154% and 69%, respectively (p < 0.01), Conclusions. The results demonstrat e that submaximal gas exchange responses to progressive exercise and r ecovery times after brief high intensity exercise are abnormal in pati ents after the Fontan procedure, These observations complement the fin dings of reduced (V) over dot(2)max observed here and by others, We sp eculate that the mechanisms for these responses are related to 1) a pe rvasive reduction in stroke volume for both low and high intensity exe rcise, 2) an abnormal linkage of ventilation to tissue carbon dioxide production, and 3) increased dependence on anaerobic metabolism in ske letal muscles, The prolonged recovery of HR and (V) over dotO(2), prov ides a possible mechanism for reduced physical activity. (C) 1998 by t he American College of Cardiology.