In Vitro Study of Flow Regulation for Pulmonary Insufficiency

Abstract

Given the tolerance of the right heart circulation to mild regurgitation and gradient, we study the potential of using motionless devices to regulate the pulmonary circulation. In addition, we document the flow performance of two mechanical valves. A motionless diode, a nozzle, a mechanical bileaflet valve, and a tilting disk valve were tested in a pulmonary mock circulatory system over the normal human range of pulmonary vascular resistance (PVR). For the mechanical valves, regurgitant fractions (RFs) and transvalvular pressure gradients were found to be weak functions of PVR. On the low end of normal PVR, the bileaflet and tilting disk valves fluttered and would not fully close. Despite this anomaly, the regurgitant fraction of either valve did not change significantly. The values for RF and transvalvular gradient measured varied from 4 to 7% and 4 to 7 mm Hg, respectively, at 5 lpm for all tests. The diode valve was able to regulate flow with mild regurgitant fraction and trivial gradient but with values higher than either mechanical valve tested. Regurgitant fraction ranged from 2 to 17% in tests extending from PVR values of 1 to 4.5 mm Hg/lpm at 5 lpm and with concomitant increases in gradient up to 17 mm Hg. The regurgitant fraction for the nozzle increased from 2 to 23% over the range of PVR with gradients increasing to 18 mm Hg. The significant findings were: (1) the mechanical valves controlled regurgitation at normal physiological cardiac output and PVR even though they failed to close at some normal values of PVR and showed leaflet flutter; and (2) it may be possible to regulate the pulmonary circulation to tolerable levels using a motionless pulmonary valve device.

In vitro simulation and validation of the circulation with congenital heart defects

“…As a verification test, the tubing length between the test section and the compliance sections on the mock right heart circuit were systematically reduced from a generous initial value while maintaining flow rate. For this test, a fluid diode, a motionless, preferred direction and resistance device was used in place of a pulmonary valve (13, 20). Instantaneous pressure and flow rate were measured and regurgitant fraction through the diode determined as shown in Fig.…”

“…The tricuspid valve is represented by an ideal diode, to block reverse flow, with a resistance and inertance in series. The pulmonary artery test section can contain a pulmonary valve, no valve, or a flow control device (13). The test section is modeled as a variable resistance and impedance, the appropriate values being different in systole versus diastole.…”

“…The system has been used to study heart valves (10) and the potential of a motionless, flow resistance device known as a fluid diode to regulate pulmonary insufficiency (13). In those studies, regurgitant fraction (RF) is extracted from the instantaneous flow rate (Q) signals as $$\text{RF}[\%]=\frac{{\text{Q}}_{\text{reverse}}}{{\text{Q}}_{\text{forward}}}\times 100$$ The instantaneous peak-peak transvalvular pressure gradient (PPG) is determined as $$PPG\left[mmHg\right]=RP{V}_{Peak}-PA{P}_{Peak}$$ Reported average values are based on a statistically stationary ensemble of 75 contiguous cycles to achieve uncertainty to within 1.2% (p< 0.025).…”

“…Comparisons of pressure and flow measurements made in vivo (left; swine model) and in vitro (right) under similar conditions using an 18 mm open cusp fluid diode as a pulmonary flow regulating device (13). …”

Imaging and patient-specific simulations for the Fontan surgery: Current methodologies and clinical applications

“…An exciting new development is the use of in vitro mock circuits to simulate the part of or the entire circulatory system. in, for example, the three stages of Fontan repair, which are currently being developed by Figliola and colleagues (see related article in this issue) (Gohean, Figliola et al 2006; Camp, Stewart et al 2007; Chiulli, Conover et al 2010). Alternatively, Steele and colleagues used an in-vivo sheep model of the Fontan circulation to quantify the effect of respiration on the pulmonary circulation and validate their coupled 1D/structured-tree representation of the pulmonary vasculature (Lucas, Ketner et al 2006; Clipp 2007).…”