Miniature Pressure Transducers Research Articles

Interlabial Contact Pressures Exhibited in Dysarthria following Traumatic Brain Injury during Speech and Nonspeech Tasks

A miniature pressure transducer was used to assess the interlabial contact pressures produced by a group of 19 adults (mean age 30.6 years) with dysarthria following severe traumatic brain injury (TBI) during a set of speech and nonspeech tasks. Ten parameters relating to lip strength, endurance, rate of movement and lip pressure accuracy and stability were measured from the nonspeech tasks. The results attained by the TBI group were compared against a group of 19 age- and sex-matched control subjects. Significant differences between the groups were found for maximum interlabial contact pressure, maximum rate of repetition of maximum pressure, and lip pressure accuracy at 50 and 10% levels of maximum pressure. In regards to speech, the interlabial contact pressures generated by the TBI group and control group did not differ significantly. When expressed as percentages of maximum pressure, however, the TBI group’s interlabial pressures appeared to have been generated with greater physiological effort.

Internal disc stresses and kinematic behavior of lumbar spine after laminotomy and laminectomy

Raj Rao, MD, Mei Wang, PhD, Peeush Singhal, MD, Linda M. McGrady, BS, Milwaukee, WI, USA; Santi Rao, MD, Fairfield, CA, USAIntroduction: The biomechanical advantage of laminotomy over the more traditional laminectomy is the preservation of the midline posterior ligaments that are important in maintaining the stability of the spine. Decompression can be effectively achieved in most cases of degenerative spinal stenosis by a laminotomy and medial facetectomy, while still preserving the uninvolved spinous process and interspinous ligaments. There have been no published studies that directly compare the amount of destabilization between the laminotomy and laminectomy procedures. More importantly, the changes in internal mechanical stresses within the intervertebral disc resulting from the two procedures have not been previously quantified. The objective of this study is to verify the presumed increase in instability associated with the laminectomy and to compare the central and peripheral intradiscal stresses after the two procedures.Methods: Nine fresh calf spines were harvested for the study. The specimen was dissected into testing segments from L4 to L6 and potted in dental cement. Four miniature pressure transducers (1.5 mm in diameter, 0.3-mm-thick disc) were inserted into nucleus, anterior annulus and posterolateral annulus to measure the internal disc stress at L4–L5 (surgical level). Pure moments in flexion, extension, lateral bending and axial rotation up to 8.5 Nm were applied to the superior vertebrae in six steps. Three-dimensional motion of each segment was measured with motion analysis system (VICON 370). The spines were tested intact first, then after laminotomy at L4–L5 and again after expanding the laminotomy into laminectomy. The range of motion of the surgical level and the inferior adjacent level were evaluated, and analysis of variance and post-hoc were performed to compare the difference between intact spine and after the two surgeries. The peak magnitudes of the intradiscal transducers for the two procedures were normalized with respect to the values of intact spine, and the difference was evaluated with paired t test.Results: Motion at the surgical level increased in all directions from laminotomy to laminectomy, and statistically significant increases were found in flexion (23%) and axial rotation (18%). The largest increase from intact spine to spines after laminotomy and laminectomy was in axial rotation (102% and 120%), followed by extension (33% and 41%) and flexion (11% and 34%). Lateral bending showed the least increase (7% and 11%). Motion at the intact inferior adjacent level remains unchanged. In flexion, the intact spine showed higher stress at the anterior annulus and the nucleus. The stress at the anterior annulus increased 20% after laminotomy, and 130% after laminectomy (p<.02). In extension, the high-stress regions were in the nucleus and posterolateral annulus. The posterolateral stress increased 22% and 27%, respectively, after each procedure, and the nucleus stress increased 24% and 31%, respectively, after laminotomy and laminectomy. The differences between the two procedures were not significant. The posterolateral stress of the loaded side in lateral bending was the highest of all loading modes. The stress remained unchanged after laminotomy but increases 9% after laminectomy (p<.06). In axial rotation, internal disc stresses were evenly distributed and unchanged after each procedure.Discussion: Previous experimental studies have shown that the posterior ligamentous structures are important in maintaining stability of the spine. Our study found that laminectomy resulted in significantly larger motion in flexion and axial rotation than laminotomy, and a significant increase in anterior annular stresses at the operated disc space, indicating anterior shifting of the loading path after laminectomy. It provides a quantitative measure of the biomechanical advantages of laminotomy over laminectomy. The increase in internal disc stresses after a laminectomy could translate clinically into degenerative changes within the disc. A better understanding of the mechanics of the spinal segment, and in particular their response to these interventions, will help diminish the clinical incidence of late development of instability and the increased need for subsequent fusions in the lumbar spine.

A fast response probe system for in-flight measurements of atmospheric turbulence

A fast response probe system for in-flight, three-dimensional measurements of atmospheric turbulence is presented. The system comprises a commercial five-hole probe connected to miniature pressure transducers by extremely short pneumatic lines. This design yields high dynamic response with negligible pneumatic transmission errors at least up to 10 Hz. The transducers are installed into a temperature-conditioned shell to eliminate thermal zero and sensitivity shifts during flight. The system has been tested on the Falcon D-CMET research aircraft of the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt, DLR) in Oberpfaffenhofen at flight altitudes up to 37 000 ft (11 278 m) and Mach numbers up to 0.75. Spectral analyses of the air-data obtained by the system confirm the predictions concerning its high frequency response capabilities. Simultaneous measurements with conventional air sensing devices installed in the aircraft provide evidence regarding the operational reliability and the accuracy of the system.

Modified Triaxial Apparatus for Shearing-Infiltration Test

Abstract A triaxial apparatus was modified and developed for performing shearing-infiltration tests under saturated and unsaturated conditions. Miniature pore-water pressure transducers were installed at different heights of the soil specimen for pore-water pressure measurement. Two different types of miniature pressure transducers were used, and problems associated with the transducers are discussed. Ancillary works and equipment to install the miniature transducers onto the soil specimen are also discussed. The measurement of air entry value of the small disk in the transducer was found to be very difficult. The results show that the soil specimen failed during infiltration due to increase in pore-water pressure or decrease in matric suction.

In vitro torsion-induced stress distribution changes in porcine intervertebral discs.

A cadaveric porcine spine motion segment experiment was conducted. To test the hypothesis that small vertebral rotations cause increased stress in the anulus while decreasing stress in the nucleus through stiffening of the anulus. Stress profiles of the intervertebral disc reportedly depend on degeneration grade and external loading. Increased stress in the anulus was found during asymmetric loading. In addition, depressurization of the nucleus combined with an instantaneous disc height increase was found when small (<2 degrees ) axial vertebral rotations were applied. Seven lumbar porcine cadaveric motion segments consisting of two vertebrae and the intervening disc with ligaments were loaded in the neutral position with 340 N of compression. Stress profiles were obtained in the neutral position, then after 0.5 degrees and 1 degrees axial rotation of the bottom vertebral body. The distribution of compressive stress in the disc matrix was measured by pulling a miniature pressure transducer through the disc along a straight path in the midfrontal plane. Stress profiles were measured in vertical (0 degrees ) and horizontal (90 degrees ) orientation. Deformation of the anulus by small axial rotations of the lower vertebra instantaneously decreased the horizontally and vertically measured stress in the nucleus while increasing stress in the anulus. A 1-hour period of creep loading decreased the stresses in the nucleus and the anulus 20% to 30%, depending on the orientation, but the effect of an increasing stress in the anular region after axial rotation persisted. The compressive Young's modulus of the composite anulus tissue increases instantaneously when small axial rotations are applied to porcine spine motion segments. This is accompanied by decreased stress in the nucleus pulposus, increased stress in the anulus fibrosus, changes in the stress profile superimposed on and independent of prolonged viscoelastic creep and dehydration, and changes in stress distribution independent of horizontal and vertical orientation.

Shock wave interaction with a spiral vortex

Previous studies on shock–vortex interactions have either been numerical in nature with idealized boundary conditions and prescribed vortex flows, or in complex experimental flow fields, such as where the vortex is shed at the trailing edge of an aerofoil. In this study a bifurcated shock tube facility has been constructed where two plane waves arrive sequentially at the trailing edge of a wedge. The first shock wave results in a spiral vortex being shed, which is then impacted by the second wave. Accurate control of the delay between the two shock waves was achieved using a highly repeatable piston actuated shock tube driver. A number of interesting new features of this interaction have been identified. The work specifically examines the development of a transient pressure spike, physically occupying an area less than 0.5 mm in diameter and having a duration of 15 μs, with a pressure nearly two-and-a-half times that of the surrounding fluid. This has been done both numerically using an adapting mesh Euler code, and experimentally, the latter with the careful use of fast response miniature pressure transducers. Numerically generated holographic interferograms and shadowgraph images have been generated for direct visual comparisons with the equivalent experimental results of the whole flow field, from which the reason for the production of the pressure spike is established as being due to local shock wave focusing resulting from part of the shock being pulled around the vortex to impact on itself. The generation of a second pressure peak is also examined, as is the wave field emanating from the interaction and the influence on the vortex. The use of both experimental images and numerical flow visualization algorithms were found to provide complimentary information, which allowed for detailed investigation and understanding of the shock wave–vortex interaction.

Analysis of Unsteady Pressure Signals on a Pitching Delta Wing

Results from wind-tunnel tests conducted on a pitching 60-deg delta wing in ramp-up motion are presented and described. The wing was instrumented with 192 miniature pressure transducers, which, in conjunction with a powerful multichannel data-logging system, allowed the distribution of time-varying surface pressures to be measured at high temporal resolution for a range of pitching cases. In addition to allowing the forward progression of vortex breakdown with incidence to be tracked, it has been possible to isolate dominant postbreakdown buffet frequencies in both the static and pitching cases. It is demonstrated that, during pitch up, these frequencies differ significantly from those of the static case, indicating that alterations in flow structure may be taking place

A minimally disruptive technique for measuring intervertebral disc pressure in vitro: application to the cervical spine

A novel technique to measure in vitro disc pressures in human cervical spine specimens was developed. A miniature pressure transducer was used and an insertion technique was designed to minimise artefacts due to insertion. The technique was used to measure the intradiscal pressure in cervical spines loaded in pure axial compression. The resulting pressure varied linearly with the applied compressive force with coefficients of determination ( r 2) greater than 0.99 for each of the four specimens. Peak pressures between 2.4 and 3.5 MPa were recorded under 800 N of compression.

Direct pressure measurements in a hyaluronan ultrafiltration concentration polarization layer

Background: The pressure distribution across a polarized layer forming during the ultrafiltration of macromolecular solutions depends on the physicochemical properties of the ultrafiltered molecule. Theoretical and experimental studies are in disagreement over the nature of this pressure profile: some predict a constant pressure distribution, while others predict a non-zero pressure gradient. Our objective was to gain insight into this issue by directly measuring both the pressure distribution and concentration profile in a hyaluronan concentration polarization layer during a model dead-end ultrafiltration experiment. Methods: A steady-state polarized layer was created by pumping solvent at a constant flow rate through a hyaluronan matrix in a specially designed filtration cell. Polymer concentration and concentration gradient were measured using a previously described laser-based refractometric technique. For purposes of this study the filtration cell incorporated an in-dwelling miniature pressure transducer that traversed the polarized layer and measured pressures. Results: Polarized layer concentration profiles were similar to those previously reported. We measured a small, but non-zero, pressure drop of 7.9 mmHg across the polarized layer (95% confidence interval: 6.6–9.3 mmHg), which can be compared with the approximately 400 mmHg pressure drop across the ultrafiltration membrane. The measured change in polarized layer pressure was of the same order as that predicted theoretically. Conclusion: The pressure profile across a hyaluronan polarized layer is non-constant, likely due to solute–solute interactions within the polarized layer. Such effects may be most pronounced for long-chain random coiling macromolecules. Further modeling of transport in such long-chain polymer matrices should take such effects into account.

Group effects in stone column foundations: model tests

Model tests have been performed to determine the mechanisms of response for beds of clay reinforced with stone columns subjected to surface footing loads. An exhumation technique has been used to discover the deformed shapes of the model stone columns and thence to deduce the way in which the columns have transferred load to the surrounding clay. Tests have explored the effect of varying the diameter, length and spacing of the model stone columns. These parameters control whether the columns act as somewhat rigid inclusions transferring load to their tips and eventually deforming either by bulging or by the formation of a failure plane, or whether they are able to compress axially or even, if sufficiently slender, to ‘bend’ and undergo significant lateral deformation. Miniature pressure transducers have been used to reveal the distribution of contact pressure between columns and clay at various stages during the loading of the footings. It appears that the columns at mid-radius of the footing are typically the most heavily loaded. Results from numerical analysis are used to provide qualitative support for some of the findings from the physical model tests.

Performance Evaluation of Non-Edible Vegetable Oils As Substitute Fuels in Low Heat Rejection Diesel Engines

Search for renewable fuels such as vegetable oils, in particular non-edible vegetable oils, has become more pertinent in the context of the fossil fuel crisis and vehicle population explosion. The drawbacks associated with vegetable oils for use in diesel engines call for a hot combustion chamber. The concept of the low heat rejection diesel engine is gaining prominence for adopting vegetable oils as substitute fuels for conventional diesel fuel. Non-edible vegetable oils such as Pongamia oil and Jatropha curcas oil are found to be efective substitute fuels in the low heat rejection diesel engine. EsteriRcation, preheating and increase in injection pressures have been tried for efective utilization of the vegetable oils. Performance parameters such as the brake specific energy consumption (b.s.e.c.) and exhaust gas temperature (EGT) have been reported for varying magnitudes of brake mean efective pressure (b.m.e.p.) with diferent non-edible vegetable oils as substitute fuels. The pollution levels of black smoke and NOx have been recorded. Combustion diagnosis is also carried out with the aid of a miniature piezoelectric pressure transducer and TDC (top dead centre) encoder.

Performance evaluation of non-edible vegetable oils as substitute fuels in low heat rejection diesel engines

Search for renewable fuels such as vegetable oils, in particular non-edible vegetable oils, has become more pertinent in the context of the fossil fuel crisis and vehicle population explosion. The drawbacks associated with vegetable oils for use in diesel engines call for a hot combustion chamber. The concept of the low heat rejection diesel engine is gaining prominence for adopting vegetable oils as substitute fuels for conventional diesel fuel. Non-edible vegetable oils such as Pongamia oil and Jatropha curcas oil are found to be efective substitute fuels in the low heat rejection diesel engine. EsteriRcation, preheating and increase in injection pressures have been tried for efective utilization of the vegetable oils. Performance parameters such as the brake specific energy consumption (b.s.e.c.) and exhaust gas temperature (EGT) have been reported for varying magnitudes of brake mean efective pressure (b.m.e.p.) with diferent non-edible vegetable oils as substitute fuels. The pollution levels of black smoke and NOx have been recorded. Combustion diagnosis is also carried out with the aid of a miniature piezoelectric pressure transducer and TDC (top dead centre) encoder.

Effects of backward bending on lumbar intervertebral discs. Relevance to physical therapy treatments for low back pain.

Mechanical testing of cadaveric motion segments. To test the hypothesis that backward bending of the lumbar spine can reduce compressive stresses within lumbar intervertebral discs. Lumbar extension affects the distribution of compressive stress inside normal cadaveric discs, but little is known about its effect on mechanically disrupted and degenerated discs. Nineteen lumbar motion segments (mean donor age, 48 years) were subjected to complex mechanical loading to simulate the following postures: moderate lumbar flexion, 2 degrees of extension, 4 degrees of extension, and the neutral position (no bending). The distribution of compressive stress within the disc matrix was measured in each posture by pulling a miniature pressure transducer along the midsagittal diameter of the disc. Stress profiles were repeated after a mechanical treatment that was intended to simulate severe disc degeneration in vivo. The "degeneration" treatment reduced pressure in the nucleus pulposus and generated stress concentrations within the anulus, in a manner similar to that found in severely degenerated discs in vivo. When all discs were considered together, 2 degrees of extension increased the maximum compressive stress within the posterior anulus by an average of 16%, compared with the neutral posture. The size of localized stress peaks within the posterior anulus was increased by 43% (P = 0.02). In 4 degrees of extension, changes observed between 0 degree and 2 degrees were usually exaggerated. In contrast, moderate flexion tended to equalize the distribution of compressive stress. In 7 of the 19 discs, 2 degrees of lumbar extension decreased maximum compressive stress in the posterior anulus relative to the neutral posture by up to 40%. Linear regression showed that lumbar extension tended to reduce stresses in the posterior anulus in those discs that exhibited the lowest compressive stresses in the neutral posture (P = 0.003; R2 = 41%). The posterior anulus can be stress shielded by the neural arch in extended postures, but the effect is variable. This may explain why extension exercises can relieve low back pain in some patients.

The Unsteady Pressure Field in a High Specific Speed Centrifugal Pump Impeller—Part II: Transient Hysteresis in the Characteristic

Hysteresis in a pump characteristic results from instability phenomena involving complex three dimensional flow with recirculation. The unsteady flow field on the top and bottom branches of a hysteresis loop in a high specific speed (ωs = 1.7) centrifugal pump characteristic was experimentally evaluated. A hypothesis for recirculation zones and prerotation as power dissipaters is proposed for explaining the discrepancy in the pressure and shaft power hysteresis. The experimental investigation was performed in both the rotating and stationary frame. In the rotating frame 25 miniature pressure transducers mounted in an impeller blade passage were sampled with a telemetry system. In the stationary frame a fast response probe was implemented. The changing impeller flow field manifested itself between the two branches of the hysteresis with increasing stochastic pressure fluctuations. Using this information the position, size, and strength of the impeller recirculation was quantitatively determined. Theoretically the rate of change of useful hydraulic power in the hysteresis regime during transient pump operation was found to be a function of throttling rate. Quasi-steady behavior existed for slow throttling, |dφ/dt| &lt; 0.005 s−1. A second-order nonlinear dependence on the throttle rate was determined for the change of useful flow power during the commencement/cessation of the impeller recirculation.

A statistical analysis of the surface pressure distribution on a delta wing

AbstractThis paper describes and presents results from static wind tunnel tests conducted on a 60° delta wing at a root chord Reynolds number of 2·7 x 106. In these tests, the wing was instrumented with 192 miniature pressure transducers which, in conjunction with a powerful multi-channel data-logging system, allowed the distribution of time-varying surface pressures to be measured at high temporal resolution. Analysis indicates that the distribution of root mean square pressure on the leeward surface of the wing can provide considerable insight into the behaviour of both the primary and secondary vortex structures. In addition, it has been established that the frequency content of pressure signals measured in the vicinity of these vortex structures is sensitive to the vortex state. It is suggested that these data features can be directly attributed to previously observed behavioral characteristics of the vortex breakdown process.

Evaluation of micro tip pressure tranducers for the measurement of intracerebral pressure transients induced by fluid percussion

We describe the application of MIKRO TIP miniature pressure transducers (MPT) for the in vivo measurement of intracerebral stresses induced by traumatic brain injury (TBI). In order to test the linearity of these transducers pressure pulses of different amplitudes (duration approximately 10ms) were generated in a closed calibration chamber. A piezoelectric pressure transducer (PPT) served as the reference measure. A linear correlation was found within the pressure range between 0.57 and 5.09 bar (R2 = 0.998). The frequency transmission characteristics of the MPTs are comparable to the PPT. In three juvenile swines (6 weeks of age) pressures within the brain tissue were induced by fluid percussion (FP) and were measured in the anterior, middle, and posterior cranial cavity as well as in the extracranial part of the medulla oblongata. The data obtained in our experiments agree with the basic biomechanics of FP known from studies in cats and rabbits. Due to their small size, MPTs can be applied in living animals. Stereotaxic positioning of these catheters at any site of the brain and spinal cord requires only minimal surgery. Therefore, MPTs are useful in evaluating animal models of brain injury and in generating input data for computational models of head injury as well as to validate the mathematical results of such models with experimental data.

Experimental determination of stress distributions in articular cartilage before and after sustained loading

Objective. To test the hypotheses that stress concentrations exist within articular cartilage, and are intensified by sustained ‘creep’ loading. Design. Matched-pair comparison of stress distributions in cartilage, in vitro, before and after creep. Background. The ability of cartilage to equalise contact stresses between articulating surfaces may be compromised by undulations in the subchondral bone, and by variations in chemical composition. Furthermore, any stress concentrations within cartilage may be affected by creep loading, which reduces its water content. Methods. Sixteen specimens of apparently normal cartilage-on-bone, 12 mm × 15 mm, were removed from the femoral condyles and tibial plateaux of patients undergoing total knee replacement. The cartilage was subjected to a nominal compressive stress of 2 MPa by means of a 10 mm-diameter flat impermeable indentor. During the 20 s loading period, a miniature pressure transducer, side-mounted in a 0.9 mm-diameter needle, was pulled through the cartilage in a direction parallel to the surface, while transducer output and position were sampled at 25 Hz. ‘Stress profiles’ were obtained with the transducer pointing in the 12 o'clock and 3 o'clock directions, and were repeated after creep loading at 1.6 MPa for 2 h. Results. Validation tests indicated that transducer output was proportional to the average compressive stress, but overestimated it by 9–15%. Stresses were greatest under the centre of the indentor, and showed local variations (‘concentrations’) which were increased in number and size after creep loading. Conclusions. Measured values of compressive stress incorporate small systematic errors. Nevertheless, the results presented clearly support both hypotheses.

Load sharing between solid and fluid phases in articular cartilage: I--Experimental determination of in situ mechanical conditions in a porcine knee.

The in situ mechanical conditions of cartilage in the articulated knee were quantified during joint loading. Six porcine knees were subjected to a 445 N compressive load while cartilage deformations and contact pressures were measured. From roentgenograms, cartilage thickness before and during loading allowed the calculation of tissue deformation on the lateral femoral condyle at different times during the loading process. Contact pressures on the articular surface were measured with miniature fiber-optic pressure transducers. Results showed that the medial side of the lateral femoral condyle had higher contact pressures, as well as deformations. To begin to correlate the pressures and resulting deformations, the intrinsic material properties of the cartilage on the lateral condyle were obtained from indentation tests. Data from four normal control specimens indicated that the aggregate modulus of the medial side was significantly higher than in other areas of the condyle. These experimental measures of the in situ mechanical conditions of articular cartilage can be combined with theoretical modeling to obtain valuable information about the relative contributions of the solid and fluid phases to supporting the applied load on the cartilage surface (see Part II).

Pressure-Volume Relationships in Sheep Mesenteric Lymphatic Vesselsin Situ:Response to Hypovolemia

We applied the principles of cardiac mechanics to study the contraction cycles of postnodal sheep mesenteric lymphatic vessels in anin situpreparation. A segment of intestinal lymphatic was isolated from lymph input and provided with Krebs solution from a reservoir. Pressure–volume relationships were assessed under various transmural pressure conditions using videomicroscopic techniques to measure diameter changes and a miniature catheter pressure transducer to monitor intralymphangion pressure. The contraction cycles were quite variable but, on average, exhibited three phases of systole and three phases of diastole with periods of isovolumetric contraction and relaxation. Elevations of transmural pressure up to 4 cm H2O resulted in significant increases in stroke volume, ejection fraction, pulse pressure, and output/minute but not contraction frequency. Regression analysis of the end systolic (ESPVR) and end diastolic pressure–volume relations (EDPVR) revealed a linear ESPVR (r2= 0.83 ± 0.03) and exponential EDPVR (r2= 0.83 ± 0.02), a result that is similar to that observed in cardiac contraction cycles. Following a 25% whole blood volume bleed (a stimulus known to enhance lymphatic pumping), significant increases in stroke volume, ejection fraction, and output/minute were observed up to transmural pressures of 4 cm H2O. While an index used to assess cardiac contractility (end systolic elastance-Ees) was not observed to change after the bleed, a shift to the left of the end-systolic pressure–volume relations compared with the sham-bled group (significant shift of regression lines for ESPVR) suggested that hemorrhage exerted a positive inotropic effect on mesenteric lymphatics.

Time-frequency analysis of transient pressure signals for a mechanical heart valve cavitation study.

A series of transient pressure signals (TPSs) can be measured using a miniature pressure transducer mounted near the tip of the inflow side of a mechanical heart valve (MHV) occluder during closure. A relationship appears to exist between the intensity and pattern of the TPS and the cavitation potential of a MHV. To study the relationship between MHV cavitation and the TPSs, we installed an MHV in a valve testing chamber of a digitally controlled burst test loop. A charge coupled device (CCD) camera and a personal computer based image grabbing program was used to visualize cavitation bubbles appearing on or near the occluder surface. One bileaflet MHV was used as the model for this study. Cavitation bubbles were observed within 300 microsec of the leaflet/housing impact. The valve was tested at various driving pressures between 100 and 1,300 mmHg. MHV cavitation bubble intensities were qualitatively classified into three categories: 1) strong, 2) weak, and 3) none. Digital images of the MHV occluder inflow surface were recorded simultaneously with the TPSs. TPSs were studied by the time-frequency analysis method (spectrogram) and correlated to MHV cavitation potential. The intensity of the cavitation bubbles was found to be associated with burst test loop driving pressures during leaflet closure.