A new membrane formulation for modelling the flow of stomatocyte, discocyte, and echinocyte red blood cells.

In this work, a numerical model that enables simulation of the deformation and flow behaviour of differently aged Red Blood Cells (RBCs) is developed. Such cells change shape and decrease in deformability as they age, thus impacting their ability to pass through the narrow capillaries in the body. While the body filters unviable cells from the blood naturally, cell aging poses key challenges for blood stored for transfusions. Therefore, understanding the influence RBC morphology and deformability have on their flow is vital. While several existing models represent young Discocyte RBC shapes well, a limited number of numerical models are developed to model aged RBC morphologies like Stomatocytes and Echinocytes. The existing models are also limited to shear and stretching simulations. Flow characteristics of these morphologies are yet to be investigated. This paper aims to develop a new membrane formulation for the numerical modelling of Stomatocyte, Discocytes and Echinocyte RBC morphologies to investigate their deformation and flow behaviour. The model used represents blood plasma using the Lattice Boltzmann Method (LBM) and the RBC membrane using the discrete element method (DEM). The membrane and the plasma are coupled by the Immersed Boundary Method (IBM). Previous LBM-IBM-DEM formulations represent RBC membrane response based on forces generated from changes in the local area, local length, local bending, and cell volume. In this new model, two new force terms are added: the local area difference force and the local curvature force, which are specially incorporated to model the flow and deformation behaviour of Stomatocytes and Echinocytes. To verify the developed model, the deformation behaviour of the three types of RBC morphologies are compared to well-characterised stretching and shear experiments. The flow modelling capabilities of the method are then demonstrated by modelling the flow of each cell through a narrow capillary. The developed model is found to be as accurate as benchmark Smoothed Particle Hydrodynamics (SPH) approaches while being significantly more computationally efficient.

Role of bird migration in the long-distance dispersal of Ixodes dammini, the vector of Lyme disease.

To evaluate the role of migratory birds in the long-distance dispersal of Ixodes dammini ticks and in the spread of Lyme disease, a 6-year study of migrating birds to an offshore New England island was conducted during 1989-1994. I. dammini are not endemic on this island, therefore allowing assessment of long-distance tick dispersal rather than local infestation. Of 11,324 spring migrants examined, 1.2% were infested with I. dammini. Of 8607 fall migrants examined, 0.2% were infested. Of nymphal ticks examined, 20% were infected with Borrelia burgdorferi. OspB DNA sequencing of 6 B. burgdorferi isolates was identical to sequences of 2 strains common in coastal Maine. It is evident that bird migration allows for long-distance dispersal of I. dammini from areas where they are endemic to areas where they are not and that a few bird species account for the majority of tick dispersal. The likelihood of establishment of enzootic Lyme disease by this mechanism is discussed.

Deaf children's processing of auditory, visual, and combined stimuli.

One hundred eighty-four deaf children were presented auditory, visual (speechreading), and combined stimuli. Some subjects showed an enhancement of their processing abilities in the combined mode, some demonstrated no improvement, and others yielded reduced scores. A method of data analysis is proposed which could contribute to a better understanding of a subject's performance.

The growing demand for midtrimester amniocentesis: a systems approach to forecasting the need for facilities.

A predicted shift in composition of the child-bearing population of the United States to higher maternal ages by year 2000 indicates that the number of chromosomally abnormal offspring of women age 35 and over will increase by 64% while the total number of women increases only 21%. We formulated a conceptual model of a health care system that predicts demand for amniocentesis from prospective patients in any particular region, the number of defective offspring detected, and the future cost of custodial care using any given level of detection effort. It was found that as capacity of clinic facilities and use by women age 35 and over in the area increased, the expenditure for amniocentesis combined with the cost of custodial care for undetected offspring decreased, assuming termination of affected pregnancies. Use of this model will enable health care managers to anticipate need for facilities, and also guide the formulation of social policy in the provision of new health services by enabling them to take into account the predictable effects of these services upon other public services.

Acoustic reflex threshold and loudness discomfort level: relationships in children with profound hearing losses.

Acoustic reflex thresholds (ART) and loudness discomfort levels (LDL) were obtained from 51 ears of 34 deaf children using broad band noise and pure tones. Both thresholds and levels were recorded using the psychophysical method of tracking. Results indicate that the relationship between ART and LDL is at variance with similar data for normal hearing individuals. Specifically, in over 39% of these deaf children LDL was obtained at a lower intensity than ART. Implications for hearing aid fitting with deaf children are discussed.