Effects of Exercise and Respiration on Blood Flow in Total Cavopulmonary Connection

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Abstract
Background— Little is known about blood flow and its relationship to respiration during exercise in patients with total cavopulmonary connection (TCPC). Methods and Results— We studied 11 patients 12.4±4.6 years (mean±SD) of age 5.9±2.8 years (mean±SD) after TCPC operation. Real-time MRI was used to measure blood flow in the superior vena cava (SVC), inferior vena cava (IVC), and ascending aorta under inspiration and expiration during supine lower-limb exercise (rest, 0.5 and 1.0 W/kg) on an ergometer bicycle. IVC and aortic flow increased from 1.60±0.52 and 2.99±0.83 L/min per m 2 at rest to 2.58±0.71 and 3.97±1.20 L/min per m 2 at 0.5 W/kg and to 3.25±1.23 and 4.62±1.49 L/min per m 2 at 1.0 W/kg ( P ≤0.05). SVC flow remained unchanged. Resting flow in the IVC was greater during inspiration (2.99±1.25 L/min per m 2 ) than during expiration (0.83±0.44 L/min per m 2 ) (inspiratory/mean flow ratio, 1.9±0.5), and retrograde flow was present during expiration (11±12% of mean flow). The predominance of inspiratory flow in IVC diminished with exercise to an inspiratory/mean flow ratio of 1.5±0.2 ( P ≤0.05) and 1.4±0.3 at 0.5 and 1.0 W/kg, respectively. Conclusions— In the TCPC, circulation IVC and aortic but not SVC flows increase with supine leg exercise. Inspiration facilitates IVC flow at rest but less so during exercise, when the peripheral pump seems to be more important.