Vibrational characterization of cavitation in left ventricular assist device.

BACKGROUND: The left ventricular assist device (LVAD) is a mechanical circulatory support device for patients with severe heart failure. Microbubbles caused by cavitation in the LVAD can potentially lead to physiological and pump-related complications. The aim of this study is to characterize the vibrational patterns in the LVAD during cavitation. METHODS: The LVAD was integrated into an in vitro circuit and mounted with a high-frequency accelerometer. Accelerometry signals were acquired with different relative pump inlet pressures ranging from baseline (+20 mmHg) to -600 mmHg in order to induce cavitation. Microbubbles were monitored with dedicated sensors at the pump inlet and outlet to quantify the degree of cavitation. Acceleration signals were analyzed in the frequency domain to identify changes in the frequency patterns when cavitation occurred. RESULTS: Significant cavitation occurred at the low inlet pressure (-600 mmHg) and was detected in the frequency range between 1800 and 9000 Hz. Minor degrees of cavitation at higher inlet pressures (-300 to -500 mmHg) were detected in the frequency range between 500-700, 1600-1700 Hz, and around 12 000 Hz. The signal power of the dominating frequency ranges was statistically significantly different from baseline signals. CONCLUSION: Vibrational measurements in the LVAD can be used to detect cavitation. A significant degree of cavitation could be detected in a wide frequency range, while minor cavitation activity could only be detected in more narrow frequency ranges. Continuous vibrational LVAD monitoring can potentially be used to detect cavitation and minimize the damaging effect associated with cavitation.

Emissions of soot, PAHs, ultrafine particles, NOx, and other health relevant compounds from stressed burning of candles in indoor air.

Burning candles release a variety of pollutants to indoor air, some of which are of concern for human health. We studied emissions of particles and gases from the stressed burning of five types of pillar candles with different wax and wick compositions. The stressed burning was introduced by controlled fluctuating air velocities in a 21.6 m3 laboratory chamber. The aerosol physicochemical properties were measured both in well-mixed chamber air and directly above the candle flame with online and offline techniques. All candles showed different emission profiles over time with high repeatability among replicates. The particle mass emissions from stressed burning for all candle types were dominated by soot (black carbon; BC). The wax and wick composition strongly influenced emissions of BC, PM2.5 , and particle-phase polycyclic aromatic hydrocarbons (PAHs), and to lower degree ultrafine particles, inorganic and organic carbon fraction of PM, but did not influence NOx , formaldehyde, and gas-phase PAHs. Measurements directly above the flame showed empirical evidence of short-lived strong emission peaks of soot particles. The results show the importance of including the entire burn time of candles in exposure assessments, as their emissions can vary strongly over time. Preventing stressed burning of candles can reduce exposure to pollutants in indoor air.

Altered stresses and dynamics after single and double annuloplasty ring for aortic valve repair.

OBJECTIVES: Aortic valve repair procedures for the treatment of isolated aortic valve insufficiency may be improved by stabilizing the functional aortic annulus using a double annuloplasty ring at the aortic annulus and sinotubular junction (STJ). The objective of this study was to compare the geometrical changes and aortic root stress distribution when using a single subvalvular ring and a double sub- and supravalvular ring in vivo. METHODS: Both the single- and double-ring procedures were performed successively in nine 80-kg pigs. Measurements were performed intraoperatively using sonomicrometry crystals in the aortic root to evaluate geometrical changes and annular and STJ force transducers measuring the segmental radial stress distribution. RESULTS: The total force in the STJ was significantly reduced after the double-ring procedure from 1.7 ± 0.6 to 0.04 ± 1.1 N (P = 0.001). The double-ring procedure significantly reduced the STJ area from 234.8 ± 37.6 to 147.5 ± 31.8 mm2 (P = 0.001) and expansibility from 17 ± 6% to 8 ± 3% (P = 0.001). With the single-ring procedure, the STJ shape was circular but became more oval with the double-ring procedure. The double-ring procedure did not affect stress distribution or geometry in the aortic annulus. CONCLUSIONS: The double-ring procedure stabilized the whole aortic root by reducing radial stress distribution in the STJ more efficiently than the single-ring procedure. Both area and expansibility were reduced with the double-ring procedure. These results confirm the importance of addressing the entire functional aortic annulus for optimal aortic valve repair procedures.

Comparison of Dacron ring and suture annuloplasty for aortic valve repair-a porcine study.

BACKGROUND: A subvalvular annuloplasty is often used for aortic valve repair in patients with isolated aortic regurgitation with aortic annulus dilatation. Our aim was to characterize and compare annulus geometry and dynamics of the Dacron ring and suture annuloplasty and compare it with the native aortic annulus under standardized conditions. METHODS: We randomized 29 pigs of 80 kg into a Dacron ring group, a suture annuloplasty group and a native control group. The assessment was performed using sonomicrometry crystals for evaluation of dynamic geometry, and pressure measurements and echocardiography to evaluate valve performance. RESULTS: Aortic annulus area (AAA) was significantly reduced in the Dacron and Suture group compared with the Native group. Expansibility was similar and within normal physiologic limits in all three groups (Native: 12%±7%; Dacron: 11%±3%; Suture: 10%±4%). The largest segmental expansion was observed at the right coronary sinus (RC) in the Native and Dacron group but in the Suture group there was no significant difference between segments. The aortic annulus was primarily oval in systole and became more circular in diastole in the Native and Dacron group, however, in the Suture group, the sphericity remained relatively unchanged throughout the cardiac cycle. CONCLUSIONS: This study is the first to describe and compare detailed segmental geometry of the Dacron ring and suture annuloplasty in a standardized porcine model. The two annuloplasties effectively downsized the aortic annulus, while expansibility was maintained. Each annuloplasty had its own geometrical characteristics, but the Dacron ring was more similar to the native aortic annulus than the suture annuloplasty. This study suggests that the Dacron ring offers a more physiological and standardized support by mimicking the geometry and dynamics of the native aortic annulus and thus is a preferable choice over the suture annuloplasty for valve-sparing aortic root procedures.

Asymmetric Dynamics of the Native Aortic Annulus Evaluated by Force Transducer and Sonomicrometry in a Porcine Model.

PURPOSE: With new repair techniques of the aortic root and valve emerging, a detailed understanding of the dynamics of the aortic annulus and valve is required for optimal results. The objective of this study was to characterize geometrical changes and force distribution of the native porcine aortic annulus throughout the cardiac cycle. METHODS: Measurements were performed in an acute 80 kg porcine model (n = 7) using sonomicrometry crystals in the aortic annulus for evaluation of geometry and dynamics, annular force transducer evaluating force distribution, and pressure measurements and echocardiography evaluating valve performance. RESULTS: Overall, segmental force distribution and geometrical changes differed between different segments of the aortic annulus. The highest force development was found at the left/right interleaflet triangle (2.87 ± 2.1 N) and the largest segmental expansion was observed at the right-coronary and left-coronary sinus. The aortic annulus changed configuration throughout the cardiac cycle and became more oval in systole. CONCLUSIONS: This study is the first to describe detailed segmental dynamics and force distribution of the native aortic annulus in a porcine model in vivo. The heterogenous behavior of the aortic annulus suggests that different segments demand different support for repair of the aortic root and valve.

In-vitro and in-vivo evaluation of a novel bioprosthetic pulmonary valve for use in congenital heart surgery.

BACKGROUND: Management of congenital malformations of the pulmonary artery and valve can be challenging. The severity often demands early intervention, which is rarely definitive due to the natural growth and multiple surgeries may be required. An artificial valve made entirely from biodegradable materials that will serve as a bioscaffold for host recellularization would be an attractive solution for these patients. Such valves have been experimentally evaluated with various results. In this study, a simple valve design supported by an absorbable proximal stabilization ring is evaluated both in-vitro and in-vivo. METHODS: From a 6.7 × 5.0 cm sheet of CorMatrix® tissue we created the valve as an inverted tubegraft with three sutured commissures. A non-closed ring of LactoSorb® basally supported the valve. The commissure height was 2 cm. Inserted as an interposition graft the valve was tested in an in-vitro model and an acute porcine model. Right ventricular and pulmonary artery pressures were recorded. RESULTS: The in-vitro testing indicated a proper opening and closure function of valve at physiological simulated hemodynamic conditions. The in-vivo evaluation showed a peak right ventricular pressure of 38 mmHg and a peak pulmonary artery pressure of 27 mmHg and thereby a peak valve gradient of 11 mmHg. The pulmonary pressure wave demonstrated a dicrotic notch indicating competence of the valve. CONCLUSION: This new pulmonary valve made entirely from biodegradable tissue worked in an acute setting and displayed a good hemodynamic profile. The valve gradient observed is equal to or superior of today's surgical treatment options.

The effect of different mitral annuloplasty rings on valve geometry and annular stress distribution†.

OBJECTIVES: To characterize the remodelling effects and deformational forces of normosized rigid, semirigid and flexible mitral annuloplasty rings after implantation in healthy pigs. METHODS: Measurements were performed in vivo with 80-kg porcine animals. Twenty-eight animals were randomized into a no ring group, a flexible ring group (Duran AnCore Ring, Medtronic, Minneapolis, MN, USA), a rigid ring group (Carpentier-Edwards Classic annuloplasty ring, Edwards Lifesciences, Irvine, CA, USA) and a semirigid ring group (Carpentier-Edwards Physio I annuloplasty ring, Edwards Lifesciences). Sonomicrometry crystals were implanted together with an annuloplasty ring and a dedicated mitral annular force transducer. The mitral annuloplasty rings were compared with respect to annular geometry and mitral annular forces. RESULTS: Cyclic changes in the mitral annulus (MA) circumference were significantly lower for all ring groups (flexible: 7 ± 3 mm, semirigid: 4 ± 2 mm and rigid: 2 ± 1 mm) compared to the no ring group (11 ± 5 mm), implying the remodelling capacity of all annuloplasty rings. The cyclic change of the MA area and the septa-lateral and inter-commissural distances were equal in the semirigid and rigid ring groups and significantly lower compared to the no ring and flexible ring groups, suggesting a stronger and equal remodelling effect in the semirigid and rigid ring groups. Forces measured in the transducer reflected the remodelling capacity of the annuloplasty rings and were in general lower for the semirigid and rigid ring groups compared to the no ring and flexible ring groups. Especially the forces in the inter-commissural direction were significantly reduced for the semirigid and rigid ring groups (semi-rigid: 1.4 ± 0.8 N, rigid: 1.2 ± 0.8 N) compared to the no ring and flexible ring groups (no ring: 3.0 ± 1.1 N, flexible: 3.4 ± 1.6 N). CONCLUSIONS: This study is the first to describe different remodelling effects and deformational forces of normosized mitral annuloplasty rings in vivo . Insights into the relationship between the remodelling effects and the accumulated forces of different mitral annuloplasty rings may have implications for ring selections in an aetiology-based mitral valve repair strategy. We propose the application of such a biomechanical approach for quantitative comparison of mitral annuloplasty rings and for future innovations on a rational basis.

Semi-rigid mitral annuloplasty rings improve myocardial stress adaptation compared to rigid rings: insights from in vitro and in vivo experimental evaluation.

OBJECTIVES: Investigate myocardial stress adaptation and remodelling capacity of a rigid and semi-rigid mitral annuloplasty ring. METHODS: The annuloplasty rings were characterized in vitro in a mechanical setup with tensile and compressive forces from 0 to 3 N. The rings were tested with and without fixation of the ring to imitate the effect of annular implantation. In vivo measurements were performed with 21 porcine animals randomized into: A no ring group, a rigid ring group (Classic Annuloplasty Ring TM , Edwards Lifesciences) and a semi-rigid ring group (Physio I Annuloplasty Ring, Edwards Lifesciences). The rings were implanted together with a force transducer and sonomicrometry was used for geometry measurements. RESULTS: The flexibility range of the semi-rigid ring was 7.6 and 2.4 mm in the septal-lateral and commissural direction, respectively. With fixation the flexibility was reduced to 1.0 and 0.6 mm, similar to the rigid ring without fixation. In vivo measurements indicated that the rigid and semi-rigid rings equally restrict the annular movement. Septal-lateral flexibility of the semi-rigid ring was not observed. Both rings induced force absorption in the ring and sutures due to the annular fixation. The absorbed forces were significantly lower for the semi-rigid ring in the posterior segment and septal-lateral direction. CONCLUSIONS: This study demonstrates the importance of correct fixation when characterizing annuloplasty rings. The annular movement of the semi-rigid ring was similar to the rigid ring when implanted at the mitral annulus as confirmed in vitro . Despite this the semi-rigid ring demonstrated a favourable stress adaptation which could potentially decrease the risk of ring dehiscence.

New mitral annular force transducer optimized to distinguish annular segments and multi-plane forces.

Limited knowledge exists about the forces acting on mitral valve annuloplasty repair devices. The aim of this study was to develop a new mitral annular force transducer to measure the forces acting on clinically used mitral valve annuloplasty devices. The design of an X-shaped transducer in the present study was optimized for simultaneous in- and out-of-plane force measurements. Each arm was mounted with strain gauges on four circumferential elements to measure out-of-plane forces, and the central parts of the X-arms were mounted with two strain gauges to measure in-plane forces. A dedicated calibration setup was developed to calibrate isolated forces with tension and compression for in- and out-of-plane measurements. With this setup, it was possible with linear equations to isolate and distinguish measured forces between the two planes and minimize transducer arm crosstalk. An in-vitro test was performed to verify the crosstalk elimination method and the assumptions behind it. The force transducer was implanted and evaluated in an 80kg porcine in-vivo model. Following crosstalk elimination, in-plane systolic force accumulation was found to be in average 4.0±0.1N and the out-of-plane annular segments experienced an average force of 1.4±0.4N. Directions of the systolic out-of-plane forces indicated movements towards a saddle shaped annulus, and the transducer was able to measure independent directional forces in individual annular segments. Further measurements with the new transducer coupled with clinical annuloplasty rings will provide a detailed insight into the biomechanical dynamics of these devices.