Environmental Electrokinetics for a sustainable subsurface.

Soil and groundwater are key components in the sustainable management of the subsurface environment. Source contamination is one of its main threats and is commonly addressed using established remediation techniques such as in-situ chemical oxidation (ISCO), in-situ chemical reduction (ISCR; most notably using zero-valent iron [ZVI]), enhanced in-situ bioremediation (EISB), phytoremediation, soil-washing, pump-and-treat, soil vapour extraction (SVE), thermal treatment, and excavation and disposal. Decades of field applications have shown that these techniques can successfully treat or control contaminants in higher permeability subsurface materials such as sands, but achieve only limited success at sites where low permeability soils, such as silts and clays, prevail. Electrokinetics (EK), a soil remediation technique mostly recognized in in-situ treatment of low permeability soils, has, for the last decade, been combined with more conventional techniques and can significantly enhance the performance of several of these remediation technologies, including ISCO, ISCR, EISB and phytoremediation. Herein, we discuss the use of emerging EK techniques in tandem with conventional remediation techniques, to achieve improved remediation performance. Furthermore, we highlight new EK applications that may come to play a role in the sustainable treatment of the contaminated subsurface.

A new method for quantitative evaluation of perceived sounds from mechanical heart valve prostheses.

Closing clicks from mechanical heart valve prostheses are transmitted to the patient's inner ear mainly in two different ways: as acoustically transmitted sound waves, and as vibrations transmitted through bones and vessels. The purpose of this study was to develop a method for quantifying what patients perceive as sound from their mechanical heart valve prostheses via these two routes. In this study, 34 patients with implanted mechanical bileaflet aortic and mitral valves (St Jude Medical and On-X) were included. Measurements were performed in a specially designed sound insulated chamber equipped with microphones, accelerometers, preamplifiers and a loudspeaker. The closing sounds measured with an accelerometer on the patient's chest were delayed 400 ms, amplified and played back to the patient through the loudspeaker. The patient adjusted the feedback sound to the same level as the 'real-time' clicks he or she perceived directly from his or her valve. In this way the feedback sound energy includes both the air- and the bone-transmitted energies. Sound pressure levels (SPLs) were quantified both in dB(A) and in the loudness unit sone according to ISO 532B (the Zwicker method). The mean air-transmitted SPL measured close to the patient's ear was 23 +/- 4 dB(A). The mean air- and bone-transmitted sounds and vibrations were perceived by the patients as an SPL of 34 +/- 5 dB(A). There was no statistically significant difference in the perceived sound from the two investigated bileaflet valves, and no difference between aortic and mitral valves. The study showed that the presented feedback method is capable of quantifying the perceived sounds and vibrations from mechanical heart valves, if the patient's hearing is not too impaired. Patients with implanted mechanical heart valve prostheses seem to perceive the sound from their valve two to three times higher than nearby persons, because of the additional bone-transmitted vibrations.

Assessment of perceived mechanical heart valve sound level in patients.

BACKGROUND AND AIM OF THE STUDY: When mechanical heart valves close, they generate an impulse that is transmitted to the patient's inner ear by two routes: (i) As acoustically transmitted sound waves; and (ii) as vibrations transmitted through bones and vessels. The aim of this study was to quantitate what patients perceive as sound from their mechanical heart valve prostheses - including both air-transmitted sound waves and bone-transmitted vibrations. METHODS: Thirty-four patients with implanted mechanical bileaflet aortic and mitral valves (St. Jude Medical and On-X) were included in the study. Measurements were performed in a specially designed sound-insulated chamber equipped with microphones, accelerometers, preamplifiers and a loud-speaker. The closing sounds measured by an accelerometer on the patient's chest were delayed 400 ms, amplified and played back to the patient through the loudspeaker. The patient adjusted the feedback sound to the same level as the 'real-time' clicks they perceived directly from their valve. In this way the feedback sound energy includes both the air- and bone-transmitted energies. Sound pressure levels (SPL) were quantitated in both dB(A) and in loudness units (sones) according to ISO 532B (Zwicker method). RESULTS: The mean air-transmitted SPL measured close to the patient's ear was 23 +/- 4 dB(A). The total air-and bone-transmitted sounds and vibrations were perceived by the patients as a SPL of 34 +/- 5 dB(A). There was no statistically significant difference in perceived sound from the two bileaflet valves investigated, and no difference between aortic and mitral valves. CONCLUSIONS: The study showed that the presented feedback method is capable of quantitating the perceived sounds and vibrations from mechanical heart valves, if the patient's hearing is not too impaired. Patients with implanted mechanical heart valve prostheses seem to perceive the sound from their valve two to four times higher than nearby persons, because of the additional bone-transmitted vibrations.

Medtronic Hall versus St. Jude Medical mechanical aortic valve: downstream turbulences with respect to rotation in pigs.

BACKGROUND AND AIMS OF THE STUDY: Turbulences downstream of mechanical aortic valves are known to contribute to most valve-related complications such as thrombosis, embolization or damage to blood components. In vitro studies have demonstrated the impact of the orientation of prostheses on transvalvular energy loss. This study evaluates the influence of valve orientation on turbulences in the supravalvular aorta in pigs. METHODS: A rotation device which could carry a Medtronic Hall (MH) or St. Jude Medical (SJM) aortic valve prosthesis (23 mm) was constructed and implanted into four healthy pigs. Turbulence measurements using pulsed Doppler ultrasonography were carried out 3 cm downstream of the valve, while the prostheses were rotated in 45 degrees steps. Reynold's normal stress values (RNS) were calculated as key markers for turbulent stresses. RESULTS: Turbulences downstream of MH and SJM valves demonstrated a significant change with rotation. The MH valve showed minimum RNSmean values with orientation of the large orifice to the right posterior aortic wall, which is the area of highest velocities during ejection. With this orientation, aortic flow almost complied with physiologic conditions. Increase of turbulence was observed with any other position. The SJM valve revealed significant turbulent flow at any orientation. Minimum RNSmean values were also measured with one orifice facing the right posterior wall of the aorta. CONCLUSION: With optimum orientation (major orifice facing the right posterior aortic wall) the MH valve matches the aortic flow pattern to near-normal physiology. The flow patterns of the SJM valve are less susceptible to rotation, but cannot attain the optimum RNS values of the MH prosthesis.

Blood velocity patterns after aortic valve replacement with a pulmonary autograft.

OBJECTIVE: Besides several other advantages, aortic valve replacement with a pulmonary autograft may result in improved hemodynamic characteristics compared to other valve replacement procedures. However, this plausible assumption has never been verified. Therefore, the aim of this study was to determine turbulent blood velocity energies in the ascending aorta after aortic valve replacement with a pulmonary autograft. METHODS: Blood velocity measurements were performed using a specialized pulsed Doppler ultrasound technique in the ascending aorta immediately after weaning from extracorporeal circulation. Six patients were included in the study. Determination of radial velocity components in 17 measuring points evenly distributed in the cross sectional area allowed computation of turbulence energies and a quantitative display of the spatial and temporal turbulence energy distribution during systole. RESULTS: The maximum turbulence energies were below 13 N/m2 in all patients and in all measuring positions in the cross sectional area. Color coded mapping of the spatial and temporal turbulence energy distribution displayed no consistent areas with markedly enhanced turbulence. These data are moderately elevated compared to turbulence energy values for normal aortic valves, which are below 4 N/m2, while artificial or xenovalves typically show values in the range of 40-60 N/m2. CONCLUSIONS: Turbulence energy levels after aortic valve replacement with a pulmonary autograft are considerably lower than those found for artificial aortic valves. From a fluid dynamic point of view this procedure provides excellent hemodynamic conditions in the ascending aorta.

Hemodynamic evaluation of a new bileaflet valve prosthesis: an acute animal experimental study.

BACKGROUND AND AIMS OF THE STUDY: A newly developed heart valve (Medtronic Parallel) was tested in an acute animal experimental model. METHODS: Five prototype valves were implanted in the aortic position in seven 90 kg pigs to enable acute evaluation of the hemodynamic performance in terms of turbulent stresses and transvalvular pressure drop. Turbulent stresses in the ascending aorta were measured using a 10 MHz perivascular Doppler echocardiographic transducer designed to measure the radical velocity component at 17 different points covering the aortic cross-sectional area. RESULTS: The drop in transvalvular peak pressure measured with fluid-filled catheters showed a non-linear relationship with cardiac output and was always < 12 mmHg. The Reynolds normal stresses were < 60 N/m2 in systole within 50 ms time windows, which is insufficient to cause mechanical damage of the formed elements of the blood. CONCLUSIONS: From a hemodynamic point of view the performance of the Medtronic Parallel aortic valve is fully acceptable and within the range of other similar, currently available mechanical valves.