Fontan Physiology Revisited

Abstract

The Fontan operation places the systemic and pulmonary circulations in series, driven by a single ventricular chamber. It has become the treatment strategy of choice for palliating single-ventricle congenital heart disease. This anatomy engenders profound changes in physiology, affecting the cardiovascular and respiratory systems with direct implications for anesthetic and intensive care. The physical basis of these changes and their sequelae are reviewed.

Inspiratory Muscle Training Is Associated With Improved Inspiratory Muscle Strength, Resting Cardiac Output, and the Ventilatory Efficiency of Exercise in Patients With a Fontan Circulation

“…The Fontan circulation, in which systemic venous return bypasses a subpulmonary ventricle, has inherent limitations of chronic elevation of central venous pressure and restricted ventricular preload . These inherent limitations may be compounded by chronotropic incompetence, nonuniform distribution of pulmonary blood flow, elevated pulmonary and systemic vascular resistance, and reduced skeletal muscle blood flow and strength . The limitations of a Fontan circulation manifest during exercise, and various parameters of exercise performance have been associated with adverse outcomes in Fontan patients …”

“…6 To our knowledge, the effects of IMT have not been reported previously in patients with a Fontan circulation. The aims of the current study in Fontan patients were to test whether IMT improved (1) inspiratory muscle strength and (2) objective measures of exercise capacity. Regarding the latter aim, we specifically tested the hypothesis that IMT improves the ventilatory efficiency of exercise, as measured by the slope of the relationship of minute ventilation (VE) to carbon dioxide production (VCO 2 ).…”

Single-Ventricle Physiology

“…They are largely dependent on skeletal muscle pump and ventilation mechanics during exercise to increase their venous return and stroke volume. 7,8 It has been demonstrated that in adults with Fontan circulation, nearly 30% of their venous flow through the pulmonary artery is dependent on respiration, whereas in patients with two ventricles this number is closer to 15%. 8,10 Due to the increase in their venous vasculature resistance, people with Fontan circulation also have a diminished venous capacitance.…”

“…7,8 It has been demonstrated that in adults with Fontan circulation, nearly 30% of their venous flow through the pulmonary artery is dependent on respiration, whereas in patients with two ventricles this number is closer to 15%. 8,10 Due to the increase in their venous vasculature resistance, people with Fontan circulation also have a diminished venous capacitance. 8,11 In people with two ventricles, approximately 70% of total blood volume is stored in the venous vasculature.…”

“…8,10 Due to the increase in their venous vasculature resistance, people with Fontan circulation also have a diminished venous capacitance. 8,11 In people with two ventricles, approximately 70% of total blood volume is stored in the venous vasculature. 8,12 Fontan patients do not have this reserve immediately available to them and this makes them susceptible to decreases in intravascular volume, or to agents that may decrease their vascular tone, either of which can decrease their pulmonary return and cardiac output.…”