Directivity of blade-tower interaction noise.

This paper presents a combined experimental and numerical study that characterises the directivity of blade-tower interaction (BTI) noise. Numerical computations were performed using a hybrid approach combining unsteady Reynolds-averaged Navier-Stokes equations and Curle's acoustic analogy, allowing the noise from the blades and the tower to be computed separately. The noise directivity of the blade and the tower components have a dipole pattern and a monopole-like pattern, respectively; hence, the resulting BTI noise directivity resembles an oval. Partial cancellations between the blade and tower components are also shown to affect the BTI noise directivity.

Consensus in Traditional Chinese Medical Diagnosis in Open Populations.

Objectives: An acceptable level of diagnostic agreement is a prerequisite for consistent administration of treatment. It is critical for investigating effectiveness of different treatment approaches using multiple practitioners. To the best of our knowledge, no previous investigation of diagnostic consensus using open populations in Chinese medicine (CM) has been reported. Investigations restricted to individual medical conditions, such as have been usually studied, do not reveal any information as to what occurs in real world clinical settings. This knowledge gap led to the current study being conducted. Design/Location/Subjects/Interventions: Investigating diagnostic agreement specifically in Traditional Chinese Medicine (TCM) in an open population, two or three practitioners diagnosed 35 subjects at the University of Technology, Sydney (UTS), TCM clinic. The practitioners were restricted to a list of the 56 most frequently used TCM diagnoses at the UTS clinic. Up to three diagnostic patterns per subject could be selected, with nominated patterns scored between 1 and 5. Outcome measures: Agreement was determined with two criteria, both expressed as simple percentages: pattern and linearly weighted agreements. Results: The results showed that 23% of practitioners obtained pattern agreement, while 19% demonstrated weighted agreement. Conclusion: There appears to be very low diagnostic agreement between practitioners. This is an important finding. If unchallenged by further investigation, the recognition of such poor diagnostic consensus may lead to rejection of TCM theory before it has been adequately assessed. Diagnostic agreement must be improved so that future investigations into treatment effectiveness or mechanisms of action are made on a valid basis. Additionally, the current TCM diagnostic format must be altered to allow the application of chance-removed statistics or the calculation of a standard error with open populations. This article is the first of a series of three that report problems in TCM diagnostic reliability and proposes solutions to the issues outlined.

Appropriate Statistics for Determining Chance-Removed Interpractitioner Agreement.

Objectives: Fleiss' Kappa (FK) has been commonly, but incorrectly, employed as the "standard" for evaluating chance-removed inter-rater agreement with ordinal data. This practice may lead to misleading conclusions in inter-rater agreement research. An example is presented that demonstrates the conditions where FK produces inappropriate results, compared with Gwet's AC2, which is proposed as a more appropriate statistic. A novel format for recording a Chinese Medical (CM) diagnoses, called the Diagnostic System of Oriental Medicine (DSOM), was used to record and compare patient diagnostic data, which, unlike the contemporary CM diagnostic format, allows agreement by chance to be considered when evaluating patient data obtained with unrestricted diagnostic options available to diagnosticians. Design: Five CM practitioners diagnosed 42 subjects drawn from an open population. Subjects' diagnoses were recorded using the DSOM format. All the available data were initially used to evaluate agreement. Then, the subjects were sorted into three groups to demonstrate the effects of differing data marginality on the calculated chance-removed agreement. Outcome measures: Agreement between the practitioners for each subject was evaluated with linearly weighted simple agreement, FK and Gwet's AC2. Results and Conclusions: In all cases, overall agreement was much lower with FK than Gwet's AC2. Larger differences occurred when the data were more free marginal. Inter-rater agreement determined with FK statistics is unlikely to be correct unless it can be shown that the data from which agreement is determined are, in fact, fixed marginal. It follows that results obtained on agreement between practitioners with FK are probably incorrect. It is shown that inter-rater agreement evaluated with AC2 statistic is an appropriate measure when fixed marginal data are neither expected nor guaranteed. The AC2 statistic should be used as the standard statistical approach for determining agreement between practitioners.

Flow-Mediated Drug Transport from Drug-Eluting Stents is Negligible: Numerical and In-vitro Investigations.

Prior numerical studies have shown that the blood flow patterns surrounding drug-eluting stents can enhance drug uptake in stented arteries. However, these studies employed steady-state simulations, wherein flow and drug transport parameters remained constant with respect to time. In the present study, numerical simulations and in-vitro experiments were performed to determine whether luminal blood flow patterns can truly enhance drug uptake in stented arteries. Unlike the aforementioned studies, the time-varying depletion of drug within the stent coating was modelled and the simulation results were validated qualitatively with the in-vitro experiments. The simulations showed that the non-Newtonian properties of blood, its complex near-wall behavior, and the pulsatility of its flow all affect drug uptake only modestly. Furthermore, flow-mediated drug transport was found to be negligible due to the rapid rate at which drug depletes at the stent coating surfaces that are exposed to arterial blood flow. For fluid dynamicists, these results show that steady-state simulations must be avoided when modelling drug transport in stented arteries. For device designers, these results may be used to optimize the shape of drug-eluting stent struts and coatings to improve stent efficacy.

A Novel Approach to Describing Traditional Chinese Medical Patterns: The "Traditional Chinese Medical Diagnostic Descriptor".

Objectives: In the first of a series of three articles by the present authors, diagnostic agreement between Traditional Chinese Medicine (TCM) practitioners was found to be low. This was the first time that TCM diagnoses had been evaluated with an open population of patients and this result is a cause of concern. In the second article, incorrect statistics were shown to have often been used to calculate chance-removed inter-rater agreement, and appropriate statistics such as Gwet's Agreement Coefficient 2 (AC2) was recommended for future studies. In this, the third article, a novel approach to recording TCM diagnostic patterns, the Traditional Chinese Medical Diagnostic Descriptor (TCMDD), is presented that allows chance-removed agreement calculation. An example of mapping TCM diagnostic patterns to the TCMDD format is given and diagnostic agreement is evaluated. Design, Settings, Subjects: The same 35 subjects used to report agreement in our first article were also diagnosed by additional practitioners using the TCMDD format during the same experimental sessions at the University of Technology, Sydney Clinic. TCM diagnoses from the first article were also mapped to the TCMDD format. Outcome measures: Linearly weighted simple agreement and the AC2 statistic were utilized and all results compared. Results: Linearly weighted simple agreement using the TCMDD and TCM mapped to TCMDD format averaged 0.80 ± 0.02 compared with 0.19 for TCM. TCMDD and TCM mapped to TCMDD chance-removed agreement, as calculated with AC2, ranged between 0.67 and 0.73 ± 0.03. Conclusions: The TCMDD allows the essence of diagnoses expressed by TCM practitioners to be appropriately compared. This was confirmed by the TCM mapped to TCMDD results. In both cases, simple agreement was significantly greater than that obtained with the TCM format. Chance-removed statistics and error estimates can be reliably calculated with the AC2 and the TCMDD in open populations.

Numerical simulation of blade-passage noise.

Numerical simulations are used to investigate the noise generated by the passage of a rotor blade past a fixed object (the blade-passage effects), which was studied by simulating a three-bladed rotor that is supported by a vertical cylindrical tower. To isolate the blade-passage effects, no incoming wind was introduced in the simulation. The symmetric blade was set to zero pitch angle relative to the plane of rotation and two blade-tower distances were investigated. The sliding mesh method was used to simulate the rotation of the blades and Curle's acoustic analogy was used to predict the noise generated from the simulated flow data. Intense force fluctuations occur during the interaction on both the tower and the passing blade, and these are the primary sources of blade-passage noise. The contribution of the force fluctuations on the support tower to blade-passage noise, which previously had been ignored, was revealed to be more significant than that of the blades. The numerical model successfully predicts the noise spectra, which are validated by the very good agreement with experimental measurements. The simulations provide a framework to better understand blade-tower interaction noise in various applications.

The Impact of Blood Rheology on Drug Transport in Stented Arteries: Steady Simulations.

BACKGROUND AND METHODS: It is important to ensure that blood flow is modelled accurately in numerical studies of arteries featuring drug-eluting stents due to the significant proportion of drug transport from the stent into the arterial wall which is flow-mediated. Modelling blood is complicated, however, by variations in blood rheological behaviour between individuals, blood's complex near-wall behaviour, and the large number of rheological models which have been proposed. In this study, a series of steady-state computational fluid dynamics analyses were performed in which the traditional Newtonian model was compared against a range of non-Newtonian models. The impact of these rheological models was elucidated through comparisons of haemodynamic flow details and drug transport behaviour at various blood flow rates. RESULTS: Recirculation lengths were found to reduce by as much as 24% with the inclusion of a non-Newtonian rheological model. Another model possessing the viscosity and density of blood plasma was also implemented to account for near-wall red blood cell losses and yielded recirculation length increases of up to 59%. However, the deviation from the average drug concentration in the tissue obtained with the Newtonian model was observed to be less than 5% in all cases except one. Despite the small sensitivity to the effects of viscosity variations, the spatial distribution of drug matter in the tissue was found to be significantly affected by rheological model selection. CONCLUSIONS/SIGNIFICANCE: These results may be used to guide blood rheological model selection in future numerical studies. The clinical significance of these results is that they convey that the magnitude of drug uptake in stent-based drug delivery is relatively insensitive to individual variations in blood rheology. Furthermore, the finding that flow separation regions formed downstream of the stent struts diminish drug uptake may be of interest to device designers.

Two-dimensional computational analysis of microbubbles in hemodialysis.

On average, an end-stage renal disease patient will undergo hemodialysis (HD) three or four times a week for 4-5 h per session. Any minor imperfection in the extracorporeal system may become significant in the treatment of these patients due to the cumulative exposure time. Recently, air traps (a safety feature of dialysis systems) have been reported to be inadequate in detecting microbubbles and may even create them. Microbubbles have been linked to lung injuries and damage to the brain in chronic HD patients; therefore the significance of microbubbles has been revisited. Bubbles may originate at the vascular access sites, sites of local turbulent blood flow, the air trap, or in the bloodlines after priming with saline prior to use. In this paper, computational fluid dynamics is used to model blood flow in the air trap to determine the likely mechanisms of microbubble dynamics. The results indicate that almost all bubbles with diameters less than 50 µm and most of the bubbles of 50-200 µm pass through the air trap. Consequently, the common air traps are not effective in removing bubbles less than 200 µm in diameter.

Parameter-optimized model of cardiovascular-rotary blood pump interactions.

A lumped parameter model of human cardiovascular-implantable rotary blood pump (iRBP) interaction has been developed based on experimental data recorded in two healthy pigs with the iRBP in situ. The model includes descriptions of the left and right heart, direct ventricular interaction through the septum and pericardium, the systemic and pulmonary circulations, as well as the iRBP. A subset of parameters was optimized in a least squares sense to faithfully reproduce the experimental measurements (pressures, flows and pump variables). Our fitted model compares favorably with our experimental measurements at a range of pump operating points. Furthermore, we have also suggested the importance of various model features, such as the curvilinearity of the end systolic pressure-volume relationship, the Starling resistance, the suction resistance, the effect of respiration, as well as the influence of the pump inflow and outflow cannulae. Alterations of model parameters were done to investigate the circulatory response to rotary blood pump assistance under heart failure conditions. The present model provides a valuable tool for experiment designs, as well as a platform to aid in the development and evaluation of robust physiological pump control algorithms.

Noninvasive average flow and differential pressure estimation for an implantable rotary blood pump using dimensional analysis.

Accurate noninvasive average flow and differential pressure estimation of implantable rotary blood pumps (IRBPs) is an important practical element for their physiological control. While most attempts at developing flow and differential pressure estimate models have involved purely empirical techniques, dimensional analysis utilizes theoretical principles of fluid mechanics that provides valuable insights into parameter relationships. Based on data obtained from a steady flow mock loop under a wide range of pump operating points and fluid viscosities, flow and differential pressure estimate models were thus obtained using dimensional analysis. The algorithm was then validated using data from two other VentrAssist IRBPs. Linear correlations between estimated and measured pump flow over a flow range of 0.5 to 8.0 L/min resulted in a slope of 0.98 ( R(2) = 0.9848). The average flow error was 0.20 +/- 0.14 L/min (mean +/- standard deviation) and the average percentage error was 5.79%. Similarly, linear correlations between estimated and measured pump differential pressure resulted in a slope of 1.027 ( R(2) = 0.997) over a pressure range of 60 to 180 mmHg. The average differential pressure error was 1.84 +/- 1.54 mmHg and the average percentage error was 1.51%.

A dynamic lumped parameter model of the left ventricular assisted circulation.

A lumped parameter model of the cardiovascular system (CVS) and its interaction with an implantable rotary blood pump (iRBP) is presented. The CVS model consists of the heart, the systemic and the pulmonary circulations. The pump model is made up of three differential equations, i.e. the motor equation, the torque equation and the hydraulic equation. Qualitative comparison with data from ex vivo porcine experiments suggests that the model is able to simulate different physiologically significant pumping states with varying pump speed set points. The combined CVS-iRBP model is suitable for use as a tool for investigating changes in the circulatory system parameters in the presence of the pump, and for testing control algorithms.