Assessment of Rheological Models Applied to Blood Flow in Human Thoracic Aorta

PURPOSE

The purpose of this study is to assess the importance of non-Newtonian rheological models on blood flow in the human thoracic aorta.

METHODS

The pulsatile flow in the aorta is simulated using the models of Casson, Quemada and Walburn-Schneck in addition to a case of fixed (Newtonian) viscosity. The impact of the four rheological models (using constant hematocrit) was assessed with respect to (i) magnitude and deviation of the viscosity relative to a reference value (the Newtonian case); (ii) wall shear stress (WSS) and its time derivative; (iii) common WSS-related indicators, OSI, TAWSS and RRT; (iv) relative volume and surface-based retrograde flow; and (v) the impact of rheological models on the transport of small particles in the thoracic aorta.

RESULTS

The time-dependent flow in the thoracic aorta implies relatively large variations in the instantaneous WSS, due to variations in the instantaneous viscosity by as much as an order of magnitude. The largest effect was observed for low shear rates (tens s-1). The different viscosity models had a small impact in terms of time- and spaced-averaged quantities. The significance of the rheological models was clearly demonstrated in the instantaneous WSS, for the space-averaged WSS (about 10%) and the corresponding temporal derivative of WSS (up to 20%). The longer-term accumulated effect of the rheological model was observed for the transport of spherical particles of 2 mm and 2 mm in diameter (density of 1200 kg/m3). Large particles' total residence time in the brachiocephalic artery was 60% longer compared to the smaller particles. For the left common carotid artery, the opposite was observed: the smaller particles resided considerably longer than their larger counterparts.

CONCLUSIONS

The dependence on the non-Newtonian properties of blood is mostly important at low shear regions (near walls, stagnation regions). Time- and space-averaging parameters of interest reduce the impact of the rheological model and may thereby lead to under-estimation of viscous effects. The rheological model affects the local WSS and its temporal derivative. In addition, the transport of small particles includes the accumulated effect of the blood rheological model as the several forces (e.g., drag, added mass and lift) acting on the particles are viscosity dependent. Mass transport is an essential factor for the development of pathologies in the arterial wall, implying that rheological models are important for assessing such risks.

Red blood cell distribution width is associated with increased interactions of blood cells with vascular wall

The mechanism underlying the association between elevated red cell distribution width (RDW) and poor prognosis in variety of diseases is unknown although many researchers consider RDW a marker of inflammation. We hypothesized that RDW directly affects intravascular hemodynamics, interactions between circulating cells and vessel wall, inducing local changes predisposing to atherothrombosis. We applied different human and animal models to verify our hypothesis. Carotid plaques harvested from patients with high RDW had increased expression of genes and proteins associated with accelerated atherosclerosis as compared to subjects with low RDW. In microfluidic channels samples of blood from high RDW subjects showed flow pattern facilitating direct interaction with vessel wall. Flow pattern was also dependent on RDW value in mouse carotid arteries analyzed with Magnetic Resonance Imaging. In different mouse models of elevated RDW accelerated development of atherosclerotic lesions in aortas was observed. Therefore, comprehensive biological, fluid physics and optics studies showed that variation of red blood cells size measured by RDW results in increased interactions between vascular wall and circulating morphotic elements which contribute to vascular pathology.

[Tapering of psychotropic drugs: current practice and needs of patients and their relatives]

BACKGROUND

The prevalence of mental illness has remained stable in recent decades, yet the use of psychotropic drugs has increased. This trend suggests that psychotropic drugs are being prescribed with an unnecessary frequency. Internationally, there is growing attention for deprescribing.

AIM

To investigate what experiences and needs patients and their loved ones/relatives have with regard to deprescribing of psychotropics.

METHOD

An online questionnaire was distributed among members of the MIND mental health care panel, which consists of (former) patients with a psychiatric disorder and their loved ones.

RESULTS

A total of 564 respondents took part in this survey. Most patients have phased out/stopped their psychotropic drugs (83.8%). This was usually done at the initiative of the patient (66.7%), in consultation with the practitioner (72.9%). The practitioner only took the initiative to deprescribe in 15.1% of the cases. In 68.6% tapering was not discussed at the start of psychotropic drug use. Patients did not experience willingness from practitioners in deprescribing, and would like to discuss deprescribing more often (79.5%).

CONCLUSION

There is an undeniable demand among patients and near ones for more emphasis on deprescribing of psychotropic drugs. We advise to include this topic in the shared decision making process.

[Multiple myeloma in an elderly patient with history of breast cancer : the value of multidisciplinary oncogeriatric collaboration]

As the prevalence of cancers increases with age, some elderly patients are confronted with multiple tumoural pathologies. The clinical case of a 70-year-old patient with adenocarcinoma of the breast and multiple myeloma complicated by severe renal failure illustrates the complexity of oncogeriatric management. The geriatric assessment makes it possible to detect frailty and provides assistance in the development of a personalized care plan while respecting the quality of life.

Flows and function of the Infant Flow neonatal continuous positive airway pressure device investigated with computational fluid dynamics

AIM

The first dedicated neonatal continuous positive airway pressure (CPAP) device using variable flow was the Infant Flow. The system was pressure stable with a low resistance to breathing. The aim of this study was to describe the flow and function of the Infant Flow geometry using simulated breathing and computational fluid dynamics.

METHOD

The original Infant Flow geometry was used with simulated term infant breathing at three levels of CPAP. The large eddy simulation methodology was applied in combination with the WALE sub-grid scale model.

RESULTS

The simulation fully resolved the flow phenomena in the Infant Flow geometry. The main flow feature during inspiration was support by gas entrainment and mixing. During expiration, the jet deflected towards the outlet with unstable impingement of the jet at the opposing edge.

CONCLUSION

The proposed mechanism has previously been based on theoretical reasoning, and our results present the first detailed description of the Infant Flow. The pressure stability was based on a jet supporting inspiration by gas entrainment and then being deflected during exhalation. This confirmed previously assumed principles of function and flows within the geometry and provided a base for further developments.

P2791Method for detection of blood clots in ventricular assist devices

Background

The technical development of modern ventricular assist devices (VAD) shows continued improvement in patient outcome. VADs continue to gain increased use not only as bridge to transplant but also as a destination therapy. However, VAD therapy is associated with complications, among which thromboembolic complications are common. Better management for early detection is paramount to improve patient outcome.

Purpose

The aims of this study were to determine if the VADs under consideration may retain clots, and to assess the feasibility of early clot detection using a non-invasive technique.

Methods

Two different VADs, the HeartMate II (HMII) and HeartMate 3 (HM3) were tested in a mock loop. Clot analogs (2 cm yarn fragments) were introduced into the loop upstream to the pump. Sound and vibration of the pump was measured using two hydrophones and at the inflow and outflow of the VAD (frequency range: 0.1Hz to 180kHz). The acoustic/vibration data was analyzed concerning the spectral content.

Results

The flow at the outflow section contained a low frequency swirling component. This appeared to be the basic flow feature. However, in the presence of clot analogs, the frequency signal was amplified. For the HMII this occurred below 10Hz. Concerning the HM3 this signal was more difficult to analyze due to HM3's non-constant rotational speed. However, by using wavelet filtering, it was possible to detect the low frequency signal in the presence of clot analogs. It was also observed that clot analogs tended to accumulate at certain regions in the respective VAD. In the HM3, clot fragments remained in a stagnation region at the bottom pump. This experimental finding contradicts published washout results based on a passive scalar model.

Conclusions

These mock loop results indicated the feasibility of early detection of blood clots in VADs by analysis of the sound/vibration induced by the clot. The signal “finger-print” needed for detection may also be possible to recover under non-continuous operational rotational speed as in the HM 3.

Detection of Thrombosis in the Extracorporeal Membrane Oxygenation Circuit by Infrasound: Proof of Concept

As of today, there exist no reliable, objective methods for early detection of thrombi in the extracorporeal membrane oxygenators (ECMO) system. Within the ECMO system, thrombi are not always fixed to a certain component or location in the circuit. Thus, clot fragments of different shapes and consistencies may circulate and give rise to vibrations and sound generation. By bedside sound measurements and additional laboratory experiments (although not detailed herein), we found that the presence of particles (clots or aggregates and fragments of clots) can be detected by analyzing the strength of infra-sound (< 20 Hz) modes of the spectrum near the inlet and outlet of the centrifugal pump in the ECMO circuit. For the few patients that were considered in this study, no clear false positive or negative examples were found when comparing the spectral approach with clinical observations. A laboratory setup provided insight to the flow in and out of the pump, confirming that in the presence of particles a low-amplitude low-frequency signal is strongly amplified, enabling the identification of a clot.

[Elder abuse: practice issues for physicians]

Elder abuse is frequent (from 4 to 6% of adults aged 65 + according to WHO). It can take various forms: psychological, financial, violation of rights, neglect and physical. Due to demographic changes, it is expected that the number of cases will increase over coming years. Scientific data show the importance of a systemic analysis of elder abuse situations in order to avoid the simplistic thinking of the "horrible abuser" and the "poor victim". A multidisciplinary team, including a physician (a general practitioner, or a specialist), is necessary. Physicians can play a role in the prevention, detection and follow up of such cases. In order to detect elder abuse, active and attentive listening is mandatory. When a possibility exists that the older adult is abused, the suspicion should be documented (per example, by using the EASI tool), in order to implement an adequate follow-up. In the French part of Belgium, specialised services can be involved: Respect Seniors (www.respectseniors.be) in Wallonia and the SEPAM d'Infor-Homes in Brussels.

A controlled follow-up study of adolescents exposed to a school shooting--psychological consequences after four months

BACKGROUND

In November 2007, a student shot eight people and himself at Jokela High School, Finland. This study aims to evaluate the long-term effects of exposure to a school shooting among adolescents.

METHOD

Associations between psychological outcomes and background factors were analysed and compared with "comparison students" four months after the incident. A questionnaire including Impact of Event Scale (IES) and General Health Questionnaire (GHQ-36) was used.

RESULTS

Half of the females and a third of the males suffered from posttraumatic distress. High level of posttraumatic distress (IES≥35), predicting PTSD, was observed in 27% of the females and 7% of the males. The odds ratio was 6.4 (95% confidence interval 3.5-10.5) for having high levels of posttraumatic distress. Severe or extreme exposure and female gender were found to increase the risk. Forty-two percent of the females and 16% of the males had psychiatric disturbance (GHQ≥9). Severe or extreme exposure, older age and female gender increased the risk. Perceived support from family and friends was found to be protective.

CONCLUSIONS

The observed risk and protective factors were similar to earlier studies. Follow-up will be essential in identifying factors predicting persisting trauma-related symptoms in adolescence.

[Geriatric day care hospital, an apport for the general practitioner in the management and follow-up of cognitive disorders]

The management of cognitive disorders requires a complex evaluation, especially since patients are frail, polypathological and because the complications are numerous. The general practitioner (GP) has an important role in detecting predictive signs but his task to specify the diagnosis and to organize the follow-up is not easy. Evaluating the patient as well as his/her surroundings and taking into account the caregivers' difficulties is necessary. The number of patients with cognitive disorders is huge and could rise with the growth of life expectancy and the increased incidence of dementia for the elderly. The geriatric day care hospital activities are developing further in Belgium since 2006 thanks to the funding of pilot projects. These structures are benefiting from a multidisciplinary team lead by a geriatrician. This paper presents what the geriatric day care hospital brings to the GP in the diagnosis and the follow-up of cognitive disorders. The geriatric day care hospital realizes diagnosis and follow-up within a suited environment. The multidisciplinary teams are used to perform complex assessment of frail patients. The various patient comorbidities are evaluated taking into account both the environment in which the patient lives and his/her caregivers. The collected data allows the setup, together with the GP, of a care plan optimizing the support of the patient and his/her surroundings.

[Elderly abuse]

Elderly abuse is still far too much ignored. A better understanding of this problem allows us to a better answer proposing an appropriate coping as well as a preventing action. This article describe this society phenomenon with is worth looking at by every health professional. Identifying such situation as elderly abuse is a very tricky process, anyway, some risk factors bound to the victims, the authors or environment can lead us to watch situations that can need to be surrounded. Elderly abuse includes physical, psychological, financial, civilian, medical abuse and neglecting. One of the reasons of the taboo around the problem is the victim's silence connected to their fears and feelings and also the circle's attitude. An acute perception of this phenomenon can lead to adequate prevention and coping. In these conditions, the " Centre d'Aide aux Personnes Agées Maltraitées" (CAPAM) can develop its listening attitude as well as pluridisciplinar team actions.

Eye Irritation Testing: The Way Forward. The Report and Recommendations of ECVAM Workshop 34

This is the report of the thirty-fourth of a series of workshops organised by the European Centre for the Validation of Alternative Methods (ECVAM). ECVAM's main goal, as defined in 1993 by its Scientific Advisory Committee, is to promote the scientific and regulatory acceptance of alternative methods which are of importance to the biosciences and which reduce, refine or replace the use of laboratory animals. One of the first priorities set by ECVAM was the implementation of procedures which would enable it to become well-informed about the state-of-the-art of non-animal test development and validation, and the potential for the possible incorporation of alternative tests into regulatory procedures. It was decided that this would be best achieved by the organisation of ECVAM workshops on specific topics, at which small groups of invited experts would review the current status of various types of in vitro tests and their potential uses, and make recommendations about the best ways forward (1). The workshop on Eye Irritation Testing: The Way Forward was held in Egham, UK, on 15-17 June 1998, under the chairmanship of Michael Balls (ECVAM, Italy). The workshop had two aims, the first of which was to review some of the previous multi-laboratory validation studies on alternatives to the Draize eye test and assess why many promising alternative methods were not successful in these studies. The second aim was to discuss strategies for making progress toward the short-term reduction, refinement, and eventual replacement, of the Draize test, including: a new approach to the validation of in vitro tests for eye irritancy, based on the use of reference standards, which promises to overcome some of the problems encountered in previous studies; the use of stepwise testing strategies which reduce and refine the use of animals in eye irritation testing; the use of multivariate and other statistical techniques for the further analysis of data generated in previous validation studies; and a programme of research aimed at understanding the underlying mechanisms of eye irritation.

Effect of topical applications of silver sulfadiazine on the natural killer cell activity in a rat model of thermal injury

The effect of topical application of silver sulfadiazine cream on the natural killer (NK) cell cytotoxicity was studied in a rat model of thermal injury. The rats were given a 30% total body surface area scald injury and the NK cell cytotoxicity was studied in rats at different days postinjury with or without treatment with silver sulfadiazine. The NK cell activity was observed to be significantly (P less than .0025) suppressed at day 7 postinjury in nontreated burned rats compared with control sham burned animals. Interestingly, in rats treated with silver sulfadiazine twice daily, no suppression in NK cell activity was observed. The application of base cream (without silver sulfadiazine) did not have any significant effect on the NK cell activity in burned rats. The data show that the effect of silver sulfadiazine on NK cell activity may be due to the sulfadiazine component, since the serum levels of sulfadiazine (33.7 +/- 1.9 micrograms/dL) were observed to be maximal at day 7 postinjury.

Mapping of a second recombination hot spot within the I-E region of the mouse H-2 gene complex

The crossover points of nine intra-I region recombinant mouse strains were determined by restriction fragment analysis. The recombinants were examined for the presence of k and p haplotype specific DNA restriction endonuclease sites. These restriction sites were a Sac I site between the E beta and E beta 2 genes, a Hpa I site within the E beta 2 gene, and a Rsa I site approximately 1 kb to the right of the E alpha gene. Seven of the recombinants were found to have crossovers between the Hpa I and the Rsa I site. This analysis suggests that a recombination hot spot exists within this segment. This segment is approximately 12-14 kb, and contains the E alpha gene and the intervening sequence between the E beta 2 and E alpha genes.

Tampon use in women with endometriosis

This study examines the potential role of vaginal tampons in women with endometriosis. In light of the fact that some medical practitioners view an appliance worn internally as a form of medical device, and in light of the recent knowledge about tampons gained during the crisis surrounding Toxic Shock Syndrome, little published information about women's menstrual patterns and practices was found. The data used here were provided by 470 members of the Endometriosis Association. These respondents' medical, surgical, and fertility case histories are stored in the Association's Data Registry housed at the Medical College of Wisconsin. Cases in this study are white; the average age is 31 +/- 5.2 years and 82 percent report use of tampons routinely. In contrast, general rates of tampon use, derived historically from several published studies using control groups matched to cases of Toxic Shock Syndrome were used for comparison. Results showed that rates of tampon use for women with endometriosis were similar to rates reported for the general population, 75 to 83 percent. We did find that within this group of mature white women, initiation of tampon use varied by age. Supporting Irwin and Millstein's study of tampon use in adolescent girls, an analysis of variance showed these women initiated tampon use at progressively earlier ages (p less than 0.001).