Exercise capacity in the Bidirectional Glenn physiology: Coupling cardiac index, ventricular function and oxygen extraction ratio

Abstract

In Bi-directional Glenn (BDG) physiology, the superior systemic circulation and pulmonary circulation are in series. Consequently, only blood from the superior vena cava is oxygenated in the lungs. Oxygenated blood then travels to the ventricle where it is mixed with blood returning from the lower body. Therefore, incremental changes in oxygen extraction ratio (OER) could compromise exercise tolerance. In this study, the effect of exercise on the hemodynamic and ventricular performance of BDG physiology was investigated using clinical patient data as inputs for a lumped parameter model coupled with oxygenation equations. Changes in cardiac index, Qp/Qs, systemic pressure, oxygen extraction ratio and ventricular/vascular coupling ratio were calculated for three different exercise levels. The patient cohort (n=29) was sub-grouped by age and pulmonary vascular resistance (PVR) at rest. It was observed that the changes in exercise tolerance are significant in both comparisons, but most significant when sub-grouped by PVR at rest. Results showed that patients over 2 years old with high PVR are above or close to the upper tolerable limit of OER (0.32) at baseline. Patients with high PVR at rest had very poor exercise tolerance while patients with low PVR at rest could tolerate low exercise conditions. In general, ventricular function of SV patients is too poor to increase CI and fulfill exercise requirements. The presented mathematical model provides a framework to estimate the hemodynamic performance of BDG patients at different exercise levels according to patient specific data.

Hemodynamic performance of tissue-engineered vascular grafts in Fontan patients

“…6a ) 22 . At both MET 3 and MET 5, OER increased above this range, consistent with behavior during exercise 23 . ePTFE graft geometry, 16 mm in Fig.…”

A computational study of the Fontan circulation with fenestration or hepatic vein exclusion

“…Migliavacca et al developed a pulsatile, closed–loop model of the Norwood circulation to explore the sensitivity of pulmonary and systemic flow to changes in different hemodynamic parameters, including heart rate and the geometry of the shunt which establishes the parallel circulation [17]. The works of Vallecilla et al used zero–dimensional models of variations on the Glenn physiology to characterize oxygen transport and other hemodynamic variables; in particular, they modeled the effect of exercise and a high altitude environment on blood flow [18,19]. Other researchers studied complications of HLHS by modeling pre– and post– surgical conditions [20].…”

Fontan procedure in patients with preoperative mean pulmonary artery pressure over 15 mmHg

“…Early closure of a systemic to pulmonary artery shunt is important, since the diastolic run off steals blood from coronary circulation which may lead to deprived performance of the future single ventricle. Moreover, bidirectional Glenn procedure is a more effective way of pulmonary gas exchange and provides better hemodynamic performance when compared with MBTS 45 . We uneventfully performed bilateral bidirectional Glenn procedure in three patients as stage‐2 palliation, which is speculated to have a worse outcome tendency in Fontan patients especially in association with pulmonary artery bifurcation stenosis 46 …”