Mini-implants for Orthodontic Anchorage: Surface Analysis after Redrilling and Sterilization - An in vitro Study.

OBJECTIVE: This study aimed to investigate, in vitro, possible alterations on mini-implants surface after retrieval and if the cleaning process and sterilization can predispose damages. MATERIALS AND METHODS: Two commercial mini-implants were tested for deformations after drilling and removing in artificial bone four times. Samples were analyzed by scanning electron microscopy, and surface alterations verified through thread and pitches deformation. To alterations caused by insertion/removal and the cleaning process and sterilization were verified in different procedures: Insertions and sterilization, only insertions, and only sterilization. Photomicrographs were analyzed in order to compare the surface characteristics. Head deformation was verified qualitatively. For a quantitative analysis, distances between threads were measured across the active part of the mini-implants. RESULTS: No deformation was observed in both groups. The cleaning and sterilization processes did not provoke alteration in both groups. Nevertheless, the presence of synthetic bone was noted in some samples. The mean distances between implant threads were similar after all steps in all regions in both groups. CONCLUSION: The results suggest that the tested mini-implants can be retrieved without damage of its surface after four cycles of insertion, removal, and sterilization. KEYWORDS: Orthodontic mini-implant, Redrilling, Sterilization. CLINICAL SIGNIFICANCE: Mini-implants can be retrieved without damage to its surface after four cycles of insertion, removal, and sterilization in the same patient without representing a biological concern.

An evaluation of non-Luer safety connectors for neuraxial procedures.

We evaluated seven non-Luer spinal needles in a two-part study. In part 1, we measured the time to see and collect simulated cerebrospinal fluid. In part 2, clinicians scored needle quality using a standardised questionnaire. The mean (SD) times to see cerebrospinal fluid varied in the lateral position from 4.2 (0.3) s (Vygon) to 25.2 (1.5) s (Sarstedt), and in the sitting position from 1.7 (0.2) s (BBraun) to 6.6 (0.3) s (Sarstedt). The time to collect cerebrospinal fluid varied from 43 (2.5) s (Vygon) to 139 (9.6) s (Pajunk) and from 19 (0.4) s (BBraun) to 34 (1.7) s (Pajunk), for the lateral and sitting positions, respectively. Median (IQR [range]) satisfaction scores in 205 needle function assessments were as follows: Sarstedt 9.0 (8.0-9.3 [5.0-10.0]); BD 8.0 (7.0-9.5 [3.0-10.0]); Pajunk 9.0 (8.0-9.8 [5.0-10.0]); Neurax 8.0 (7.0-9.0 [2.0-9.0]); Smiths 8.0 (7.0-9.0 [4.0-10.0]); Vygon 8.0 (7.5-9.0 [5.0-10.0]); and BBraun 9.0 (9.0-10.0 [7.0-10.0]). The difference in satisfaction scores between the BBraun and Neurax was significant (p < 0.01). A number of recurrent problems were found during the evaluation. The variation in time to collect cerebrospinal fluid samples may have implications for non-anaesthetic practice. This evaluation provides a baseline to assist others in commencing their procurement process.

The impact of an emergency hiring plan on the shortage and distribution of nurses in Kenya: the importance of information systems.

OBJECTIVE: To analyse the effect of Kenya's Emergency Hiring Plan for nurses on their inequitable distribution in rural and underserved areas. METHODS: We used data from the Kenya Health Workforce Informatics System on the nursing workforce to determine the effect of the Emergency Hiring Plan on nurse shortages and maldistribution. The total number of nurses, the number of nurses per 100,000 population and the opening of previously closed or new heath facilities were recorded. FINDINGS: Of the 18,181 nurses employed in Kenya's public sector in 2009, 1836 (10%) had been recruited since 2005 through the Emergency Hiring Plan. Nursing staff increased by 7% in hospitals, 13% in health centres and 15% in dispensaries. North Eastern province, which includes some of the most remote areas, benefited most: the number of nurses per 100,000 population increased by 37%. The next greatest increase was in Nyanza province, which has the highest prevalence of HIV infection in Kenya. Emergency Hiring Plan nurses enabled the number of functioning public health facilities to increase by 29%. By February 2010, 94% of the nurses hired under pre-recruitment absorption agreements had entered the civil service. CONCLUSION: The Emergency Hiring Plan for nurses significantly increased health services in Kenya's rural and underserved areas over the short term. Preliminary indicators of sustainability are promising, as most nurses hired are now civil servants. However, continued monitoring will be necessary over the long term to evaluate future nurse retention. The accurate workforce data provided by the Kenya Health Workforce Informatics System were essential for evaluating the effect of the Emergency Hiring Plan.

Effect of inhibition of MAO and COMT on intrarenal dopamine and serotonin and on renal function.

The purpose of the present investigation was to study the effects of inhibition of monoamine oxidase (MAO) and/or catechol-O-methyltransferase (COMT), enzymes involved in the degradation of dopamine (DA) and serotonin (5-HT), on intrarenal DA and 5-HT, as reflected in the renal interstitial fluid (RIF) microdialysate and urine, and on renal function. Inhibition of MAO selectively increased RIF 5-HT from 3.16 +/- 0.38 to 8.03 +/- 1.83 pg/min (n = 7, P < 0.05), concomitant with decreases in mean arterial blood pressure and glomerular filtration rate (2.09 +/- 0. 18 to 1.57 +/- 0.22 ml/min, n = 7, P < 0.05). Inhibition of COMT significantly increased RIF DA (3.47 +/- 0.70 to 8.68 +/- 1.96 pg/min, n = 9, P < 0.05), urinary DA (2.00 +/- 0.16 to 2.76 +/- 0.26 ng/min, n = 9, P < 0.05), and absolute excretion of sodium (6.42 +/- 2.00 to 9.82 +/- 1.62 micromol/min, n = 10, P < 0.05). Combined inhibition of MAO and COMT significantly increased RIF DA, urinary DA, and urinary 5-HT, which was accompanied with increases in urine flow rate, and absolute (3.03 +/- 0.59 to 8.40 +/- 1.61 micromol/min, n = 9, P < 0.01) and fractional excretion of sodium. We conclude that inhibition of MAO selectively increases RIF 5-HT. COMT appears to be more important than MAO in the metabolism of intrarenal DA. Physiological increases in intrarenal DA/5-HT induced by inhibition of their degrading enzymes are accompanied with significant alterations of renal function.

The role of Brachyury (T) during gastrulation movements in the sea urchin Lytechinus variegatus.

The studies described here sought to identify and characterize genes involved in the gastrulation and morphogenetic movements that occur during sea urchin embryogenesis. An orthologue of the T-box family transcription factor, Brachyury, was cloned through a candidate gene approach. Brachyury (T) is the founding member of this T-box transcription factor family and has been implicated in gastrulation movements in Xenopus, zebrafish, and mouse embryogenesis. Polyclonal serum was generated to LvBrac in order to characterize protein expression. LvBrac initially appears at mesenchyme blastula stage in two distinct regions with embryonic expression perduring until pluteus stage. Vegetally, LvBrac expression is in endoderm and lies circumferentially around the blastopore. This torus-shaped area of LvBrac expression remains constant in size as endoderm cells express LvBrac upon moving into that circumference and cease LvBrac expression as they leave the circumference. Vegetal expression remains around the anus through pluteus stage. The second domain of LvBrac expression first appears broadly in the oral ectoderm at mesenchyme blastula stage and at later embryonic stages is refined to just the stomodael opening. Vegetal LvBrac expression depends on autonomous beta-catenin signaling in macromeres and does not require micromere or veg2-inductive signals. It was then determined that LvBrac is necessary for the morphogenetic movements occurring in both expression regions. A dominant-interfering construct was generated by fusing the DNA binding domain of LvBrac to the transcriptional repression module of the Drosophila Engrailed gene in order to perturb gene function. Microinjection of mRNA encoding this LvBrac-EN construct resulted in a block in gastrulation movements but not expression of endoderm and mesoderm marker genes. Furthermore, injection of LvBrac-EN into one of two blastomeres resulted in normal gastrulation movements of tissues derived from the injected blastomere, indicating that LvBrac downstream function may be nonautonomous during sea urchin gastrulation.

Role of adenosine in contrast media-induced acute renal failure in diabetes mellitus.

Increased release of renal adenosine and stimulation of renal adenosine receptors have been proposed to be major mechanisms in the development of contrast media-induced acute renal failure (CM-ARF). Patients with diabetes mellitus or preexisting renal disease who have reduced renal function have a markedly increased risk to develop CM-ARF. This increased risk to develop CM-ARF in patients with diabetes mellitus is linked to a higher sensitivity of the renal vasculature to adenosine, since experimental studies have shown increased adenosine-induced vasoconstriction in the kidneys of diabetic animals. Furthermore, recent evidence suggests that administration of adenosine receptor antagonists reduces the risk of development of CM-ARF in both diabetic and nondiabetic patients. The purpose of this review is to discuss the role of adenosine in the development of CM-ARF, particularly in the kidneys of diabetic patients, and to evaluate the therapeutic potential of adenosine receptor antagonists in the prevention of CM-ARF. Selective adenosine A1 receptor antagonists may provide a therapeutic tool to prevent CM-ARF in patients with diabetes mellitus and reduced renal function.

Natriuretic response to increased pressure is preserved with COX-2 inhibitors.

Elevation of renal interstitial hydrostatic pressure (RIHP) by direct renal interstitial volume expansion increases sodium excretion. This natriuretic response is blunted by the nonspecific inhibition of the cyclooxygenase (COX) enzymes. The present study tested the hypothesis that the natriuretic response to increased RIHP during direct renal interstitial volume expansion is dependent on COX-1 but not COX-2. RIHP and fractional excretion of sodium (FE(Na)) were measured before and after direct renal interstitial volume expansion in control rats (n=7), rats infused with the COX-1 inhibitor piroxicam (n=6, 1.5 mg/kg), and rats infused with the COX-2 inhibitors NS-398 (n=5, 1.5 mg/kg) and meloxicam (n=6, 0.3 mg/kg). In control animals, direct renal interstitial volume expansion significantly increased RIHP (Delta2.3+/-0.5 mm Hg, P<0. 05) and FE(Na) (Delta1.1+/-0.3%, P<0.05). Likewise, in animals infused with NS-398 or meloxicam, direct renal interstitial volume expansion significantly increased RIHP (Delta1.8+/-0.6 mm Hg, P<0.05, and Delta1.7+/-0.3 mm Hg, P<0.05) and FE(Na) (Delta1.5+/-0.4%, P<0. 05, and Delta1.1+/-0.3%, P<0.05), respectively. In contrast, infusion of piroxicam significantly blunted the natriuretic response to direct renal interstitial volume expansion (DeltaFE(Na) 0.3+/-0. 2%), even though RIHP was increased (Delta1.9+/-0.6 mm Hg, P<0.05). Infusion of piroxicam but not NS-398 or meloxicam blunted the natriuretic response to increased renal interstitial hydrostatic pressure, suggesting that the natriuretic response to increased blood pressure may be preserved during inhibition of COX-2.

Adenosine-induced renal vasoconstriction in diabetes mellitus rats: role of prostaglandins.

We investigated the role of prostaglandins in the renal vascular response to exogenous and endogenous adenosine in control and streptozotocin (STZ) diabetic rats. Exogenous adenosine (0.01-100 nmol) injected into the abdominal aorta decreased renal blood flow (RBF) in a dose-dependent manner to a much greater extent in STZ rats than in control rats (P < 0.001). Inhibition of prostaglandin synthesis with indomethacin (Indo; 10 mg/kg iv) potentiated the adenosine-induced renal vasoconstriction in control rats but not in STZ rats. In control rats, Indo shifted the dose response curve of exogenous adenosine-induced RBF reductions to the left by a factor of 10 (ED(50): from 5.5 +/- 0.51 to 0.55 +/- 0.07 nmol adenosine, n = 6, P < 0.001) and in STZ rats only by a factor of two (ED(50): from 0.32 +/- 0.03 to 0.16 +/- 0.02 nmol adenosine, n = 6, P > 0.05). The renal response to endogenous adenosine was assessed by the magnitude of the postocclusive reduction of RBF (POR), an adenosine-mediated phenomenon. POR was greater in STZ rats (-65.3 +/- 5.2%, P < 0.001) compared with control rats (-36.2 +/- 3.5%). Indo markedly enhanced POR in control rats (-20.3 +/- 3.7%) but not in STZ rats (-4.5 +/- 2.7%). Renal cortical and medullary PGE(2) microdialysate concentrations and urinary PGE(2) excretions were clearly not lower in STZ (cortex: 169 +/- 61 pg/ml; medulla: 640 +/- 88 pg/ml, urine: 138 +/- 25 pg/min) compared with control rats (cortex: 99 +/- 12 pg/ml; medulla: 489 +/- 107 pg/ml; urine: 82 +/- 28 pg/min). Indo significantly decreased renal cortical, medullary, and urinary excretion of PGE(2) in STZ and control rats. These findings demonstrate that the adenosine-induced renal vasoconstriction is increased in the presence of Indo in control rats but not in STZ rats. The observations suggest that the diabetic renal vasculature may have a diminished vasodilatory capacity in response to prostaglandins to counteract adenosine-induced renal vasoconstriction.

A back-propagation neural network predicts absorption maxima of chimeric human red/green visual pigments.

The absorption spectra of human red and green visual pigments have peak wavelengths, lambda max, that differ by 31 nm, yet the opsins differ in only 15 amino acids. Mutagenesis studies have demonstrated that seven of the 15 amino acids determine the spectral shift. We trained neural networks to predict the lambda max of any red/green chimeric protein. Seven mutants were excluded from the original training set. The trained networks were able to predict the lambda max for the excluded mutants. As an additional test, five new chimeric pigments were constructed and lambda max determined. The neural networks correctly predicted the lambda max of all five mutants. The use of neural networks is a novel approach to the problem of wavelength modulation in visual pigments.

Prenylation-dependent association of Ki-Ras with microtubules. Evidence for a role in subcellular trafficking.

We recently identified a prenyl peptide-binding protein in microsomal membranes from bovine brain (Thissen, J. A., and Casey, P. J. (1993) J. Biol. Chem. 268, 13780-13783). Through a variety of approaches, this binding protein has been identified as the cytoskeletal protein tubulin. Prenyl peptides bind to purified tubulin with a Kd of 40 nM and also bind to tubulin polymerized into microtubules. Microtubule affinity chromatography of extracts from cells in which the prenyl protein pool was metabolically labeled revealed that prenyl proteins bound to the immobilized microtubules; one, a 24-kDa protein, was tentatively identified as a GTP-binding protein. Of several prenylated GTP-binding proteins tested, including Ki-Ras4B, Ha-Ras, RhoB, RhoA, and Rap1B, only Ki-Ras was found to bind significantly to microtubules, and this was in a prenylation-dependent fashion. A potential significance of the interaction of Ki-Ras4B with microtubules was indicated from analysis of the localization of newly synthesized Ki-Ras4B and Ha-Ras, each tagged with green fluorescence protein (GFP). Treatment of NIH-3T3 cells expressing GFP-Ki-Ras with Taxol (paclitaxel) resulted in accumulation of the expressed protein in intracellular locations, whereas in control cells the protein was correctly targeted to the plasma membrane. Importantly, such treatment with paclitaxel did not affect the cellular localization of expressed GFP-Ha-Ras. These results indicate that an intact microtubule network may be directly involved in Ki-Ras processing and/or targeting and provide direct evidence for a physiological distinction between Ki-Ras and Ha-Ras in cells. Additionally, the finding that paclitaxel treatment of cells disrupts Ki-Ras trafficking suggests an additional mechanism for the anti-proliferative effects of this drug.

Promoting group psychotherapy in managed care: basic economic principles for the clinical practitioner.

Knowledge of the basic economic factors underlying managed mental health care directly impacts the clinical practitioners' ability to make constructive changes in the system. To aid understanding this article introduces the managed care marketplace model, the interactive relationship between medical necessity and patient co-payment, and demand management economics. The author encourages practitioners to develop strategies to overcome specific economic obstacles that prevent the promotion of group psychotherapy.

A microstructural flow analysis within a bileaflet mechanical heart valve hinge.

BACKGROUND AND AIMS OF THE STUDY: During recent clinical trials, the Medtronic Parallel bileaflet heart valve was found to have an unacceptable thrombosis complication rate. As patient- and material-related factors proved negative causes for this outcome, it was hypothesized that the flow fields within the valve's hinge pocket contributed to the thrombus formation. METHODS: A microstructural flow analysis within the hinge pocket is presented which uses the techniques of flow visualization, computational fluid dynamics (CFD), and laser Doppler velocimetry (LDV). The application of these techniques towards solving this problem has become possible through (i) the ability to manufacture dimensionally correct 1-X transparent heart valve housings, (ii) advances in CFD technology, and (iii) advances in LDV measurement techniques. RESULTS: This analysis showed that a vortex was present at the hinge pocket's inflow channel during forward flow and degenerated to a disturbed three-dimensional structure during reverse flow with zones of turbulent shear stress large enough to cause blood cell damage. In addition, multiple zones of flow stagnation and disturbed flow existed along the leaflet's pivot throughout the entire cardiac cycle. It was felt that these complex fluid structures created conditions which resulted in the formation of thrombus within the hinges of the Medtronic Parallel valve. These findings were supported by limited clinical explant data which illustrated early thrombus formation within the Parallel valve's hinge pocket at sites predicted by the analysis. CONCLUSIONS: This study provides, for the first time, an understanding of the detailed flow structures within the hinges of a mechanical heart valve and demonstrates an analysis technique by which future mechanical heart valve designs may be assessed for the potential of thrombus formation within the valve's hinge regions.

Material properties, biocompatibility, and wear resistance of the Medtronic pyrolytic carbon.

Pyrolytic carbon is the material of choice for components in the majority of heart valves available today. Many manufacturers have vertically integrated their manufacturing capabilities to include their own carbon manufacturing facilities. Medtronic is no exception. Because of the critical nature of pyrolytic carbon to the success of a valve design, a series of in vitro tests were conducted to determine the relative equivalence of Medtronic and CarboMedics, Inc. (CMI) pyrolytic carbon based on the Medtronic HallTM design. Correlation between in vivo and in vitro pyrolytic carbon wear is provided based on an analysis of explanted Medtronic Hall discs manufactured by CMI. Material, physical, chemical, and biocompatibility proprieties for Medtronic carbon were determined using standardized techniques. Structural integrity of the discs was evaluated by accelerated cyclic testing to determine depth of wear characteristics. Explanted valves were subjected to identical depth of wear analysis. No statistical difference was found between CMI and Medtronic pyrolytic carbon discs based on mechanical and physical properties and depth of wear on both inflow and outflow disc surfaces. Furthermore, evaluation of CMI discs after explant from human subjects confirms similar wear characteristics with a half life in excess of the 570 years projected from the in vitro experiments. In summary, material properties, structural integrity and biocompatibility testing conducted on heart valve discs made by Medtronic showed results virtually identical to those from testing of discs made by CMI.

Can cavitation bubbles generated by mechanical heart valves be detected by transcranial Doppler?

Increasingly, transcranial Doppler (TCD) systems are being considered as potential tools to determine the thrombogenicity of herat valve prostheses and/or to serve as early warnings of impending thromboembolic strokes. TCD is thought to detect the presence of intracranial arterial microemboli based on high intensity signals (HITS). While the exact cause of these HITS is not known, it has been theorized that they are due in part to mechanical valve induced cavitation. To determine if this is correct, in vitro experiments were conducted to find if TCD could detect mechanical valve induced cavitation bubbles. An in vitro flow system was developed in which 29mm Medtronic Hall, St. Jude Medical and Medtronic Intact valves, one each, were simultaneously subjected to validated non-cavitation and cavitation generating conditions. Polystyrene particles as well as air bubbles were infused into the flow system to provide controls for comparison. The flow field proximal to each valve was interrogated using TCD sample volumes located 2.5 cm proximal to, 1.3 cm proximal to, and at the valvular inflow surface. The TCD system accurately detected both infused air bubbles and polystyrene particles at all sample volume locations. Under known cavitation generating conditions without infused air bubbles, the TCD failed to register HITS at any sample volume location. Even though cavitation at the valve surface might have been masked by a "system generated artifact", cavitation formed bubbles must persist and pass through the two proximal sample volumes if they were to be captured intracranially. These data suggest that the TCD is unable to detect mechanical valve induced cavitation bubbles either because the bubbles are too small, too few, or too short lived. It is therefore probable that clinically recorded HITS associated with mechanical valves are from origins other than valve induced cavitation bubbles.

A non-invasive technique to quantify in vitro bioprosthetic valvular coaptation.

The functional relationship between valvular leaflet stress and coaptive geometry may provide insight into a bioprosthetic heart valve's ability to maintain coaptation under a broad range of physiologic operating conditions. Previous investigators have only indirectly measured coaptation geometry. A non-invasive in vitro technique is demonstrated to directly quantify the coaptive geometry of bioprosthetic heart valves. A discussion is provided detailing the use of this information in a finite element model to determine the functional relationship between valvular leaflet stress and coaptation geometry. Video images of the stent post deflections and coaptive geometry for size 21 mm, 23 mm, and 25 mm Hancock Aortic Pericardial heart valves are obtained based on back light illumination of each valve's coaptive area at discrete back pressures. The resulting images are analyzed using image processing and motion analysis techniques. Results indicate that at back pressures greater than 50-75 mmHg the coaptive area remains constant. There is a decrease in coaptive depth at the valve's periphery, whereas the point of maximum coaptation maintains position approximately midway along the free margin. Good agreement is found between the experimentally determined and finite element model's predicted coaptation geometry.

Venturi pressure cannot cause cavitation in mechanical heart valve prostheses.

Surface pitting of certain mechanical heart valve (MHV) explants has prompted investigation into possible causes of cavitation during MHV operation. Leaflets of a 29 mm MHV were glued shut with B-datum (BD) gaps fixed at 0.0089, 0.0174, and 0.0219 cm. Each BD gap setting was tested in a steady flow chamber, with leakage flow established at transvalvular pressures (delta P) of 20 to 200 mmHg. Laser Doppler velocimeter (LDV) velocity measurements were recorded 220 microns distal to the BD, along with leakage flowrates. Maximum LDV velocities were compared with those calculated using the mass conservation equation. At identical P, the LDV flow velocities for the three BD settings were found to be approximately equal. This indicates a geometric independence of the leakage flow velocity. At atmospheric pressure, the local velocity necessary to cavitate blood as a liquid is approximately 13 m/sec. These results demonstrate that the leakage velocity is insufficient to cause cavitation. A simplified theoretical model is proposed to illustrate the necessary delta P to produce Venturi related cavitation.

IFN-gamma and LPS overcome glucocorticoid inhibition of priming for superoxide release in human monocytes. Evidence that secretion of IL-1 and tumor necrosis factor-alpha is not essential for monocyte priming.

We examined the interaction between IFN-gamma, LPS, and glucocorticoids on release of oxygen radicals by human monocytes cultured in vitro. After 48 h culture, monocytes released low amounts of superoxide anion (O2-) when stimulated by PMA or FMLP. Monocytes incubated with either IFN-gamma or LPS became "primed" and released greater amounts of O2- in response to stimuli. Monocytes incubated with hydrocortisone, methylprednisolone, dexamethasone, or prednisolone alone showed decreased release of O2-. Prednisone and progesterone, which are not active glucocorticoids, had no effect. When glucocorticoids were co-incubated with IFN-gamma or LPS, the effect of hydrocortisone and other active steroids was blocked, and the monocytes released high O2-. However, when monocytes were preincubated with hydrocortisone for 24 h before addition of IFN-gamma or LPS, priming for enhanced O2- production by LPS was partially inhibited whereas there was no effect on IFN-gamma priming. We suggest that IFN-gamma and LPS can block the anti-inflammatory effects of glucocorticoids, contributing to increased inflammation at tissue sites; however, the mechanism of this effect may differ for the two macrophage activators. To investigate the mechanisms of priming by IFN-gamma and LPS, we examined the effects of these agents and of hydrocortisone on secretion of IL-1 and TNF-alpha. Both IL-1 and TNF-alpha primed monocytes for enhanced release of O2- in response to PMA. LPS caused monocytes to secrete both IL-1 beta and TNF-alpha. LPS-induced secretion of TNF-alpha and IL-1 beta was completely blocked by hydrocortisone, but the priming effect of LPS on O2- release was only partly blocked. IFN-gamma did not cause monocytes to secrete IL-1 beta or TNF-alpha, under our culture conditions (mononuclear cells cultured in Teflon in endotoxin-free modified Earle's salt solution without serum). Therefore, priming by LPS and IFN-gamma, and the inhibition of priming by glucocorticoids involve mechanisms that extend beyond regulation of secretion of IL-1 and TNF-alpha.

Vortex shedding in bileaflet heart valve prostheses.

A dynamic study of two geometrically similar bileaflet heart valve prostheses (HVP) was performed using a physiologic mock circulatory flow loop. The HVPs studied were the 25 mm St. Jude Medical (SJM) and the 25 mm Carbomedics (CMI) in the aortic position and the 27 mm SJM and 27 mm CMI in the mitral position. All data were collected at a heart rate of 70 beats/min and a cardiac output of 5.0 L/min. Flow visualization was conducted in the transparent flow chambers of the pulsatile mock circulatory flow loop using a 15 mW He-Ne laser light source. A cylindrical lens and optics system converted the incident laser beam into a thin parallel light plane, and 420 microns tracer particles were suspended in the testing fluid to illuminate the flow field at selected planes. Frame-by-frame analysis of the 16 mm high-speed cine provides detailed phasic flow patterns in the vicinity of the HVP. A series of still photographs of flow patterns, taken at approximately 22.5 degrees phase intervals, are sequentially presented for each HVP. In the aortic position, a Karman-like vortex pattern appears downstream of the SJM at the end of the ejection phase. The CMI exhibits a rather symmetrical ejection flow pattern that turns into random motion immediately after the onset of ejection. In the mitral position, the SJM again exhibits a strong core flow during ventricular filling, whereas the CMI produces a more diffuse pattern during the same period. A pair of vortices shed from both the SJM and CMI are clearly visible toward the end of the ventricular filling phase. The vortex mechanisms are discussed in light of leaflet boundary layer formation.