Volumetric lattice Boltzmann method for wall stresses of image-based pulsatile flows.

Image-based computational fluid dynamics (CFD) has become a new capability for determining wall stresses of pulsatile flows. However, a computational platform that directly connects image information to pulsatile wall stresses is lacking. Prevailing methods rely on manual crafting of a hodgepodge of multidisciplinary software packages, which is usually laborious and error-prone. We present a new computational platform, to compute wall stresses in image-based pulsatile flows using the volumetric lattice Boltzmann method (VLBM). The novelty includes: (1) a unique image processing to extract flow domain and local wall normality, (2) a seamless connection between image extraction and VLBM, (3) an en-route calculation of strain-rate tensor, and (4) GPU acceleration (not included here). We first generalize the streaming operation in the VLBM and then conduct application studies to demonstrate its reliability and applicability. A benchmark study is for laminar and turbulent pulsatile flows in an image-based pipe (Reynolds number: 10 to 5000). The computed pulsatile velocity and shear stress are in good agreements with Womersley's analytical solutions for laminar pulsatile flows and concurrent laboratory measurements for turbulent pulsatile flows. An application study is to quantify the pulsatile hemodynamics in image-based human vertebral and carotid arteries including velocity vector, pressure, and wall-shear stress. The computed velocity vector fields are in reasonably well agreement with MRA (magnetic resonance angiography) measured ones. This computational platform is good for image-based CFD with medical applications and pore-scale porous media flows in various natural and engineering systems.

Three-dimensional poor man's Navier-Stokes equation: a discrete dynamical system exhibiting k(-5/3) inertial subrange energy scaling.

Outline of the derivation and mathematical and physical interpretations are presented for a discrete dynamical system known as the "poor man's Navier-Stokes equation." Numerical studies demonstrate that velocity fields produced by this dynamical system are similar to those seen in laboratory experiments and in detailed simulations, and they lead to scaling for the turbulence kinetic energy spectrum in accord with Kolmogorov K41 theory.

Magnetic resonance imaging of the upper airway structure of children with obstructive sleep apnea syndrome.

The anatomical relationships between lymphoid, bony, and other tissues affecting the shape of the upper airway in children with obstructive sleep apnea syndrome (OSAS) have not been established. We therefore compared the upper airway structure in 18 young children with OSAS (age 4.8 +/- 2.1 yr; 12 males and 6 females) and an apnea index of 4.3 +/- 3.9, with 18 matched control subjects (age, 4.9 +/- 2.0 yr; 12 males and 6 females). All subjects underwent magnetic resonance imaging under sedation. Axial and sagittal T1- and T2-weighted sequences were obtained. Images were analyzed with image-processing software to obtain linear, area, and volumetric measurements of the upper airway and the tissues comprising the airway. The volume of the upper airway was smaller in subjects with OSAS in comparison with control subjects (1.5 +/- 0.8 versus 2.5 +/- 1.2 cm(3); p < 0.005) and the adenoid and tonsils were larger (9.9 +/- 3.9 and 9.1 +/- 2.9 cm(3) versus 6.4 +/- 2.3 and 5.8 +/- 2.2 cm(3); p < 0.005 and p < 0.0005, respectively). Volumes of the mandible and tongue were similar in both groups; however, the soft palate was larger in subjects with OSAS (3.5 +/- 1.1 versus 2.7 +/- 1.2 cm(3); p < 0.05). We conclude that in children with moderate OSAS, the upper airway is restricted both by the adenoid and tonsils; however, the soft palate is also larger in this group, adding further restriction.

Magnetic resonance imaging of the upper airway in children with Down syndrome.

As compared with control subjects, children with Down syndrome have different size and shape relationships among tissues composing the upper airway, which may predispose them to obstructive sleep apnea (OSA). We hypothesized that Down syndrome children without OSA have similar subclinical differences. We used magnetic resonance imaging to study the upper airway in 11 Down syndrome children without OSA (age, 3.2 +/- 1.4 yr) and in 14 control subjects (age, 3.3 +/- 1.1 yr). Sequential T1- and T2-weighted spin-echo axial and sagittal images were obtained. We found a smaller airway volume in subjects with Down syndrome (1.4 +/- 0.4 versus 2.3 +/- 0.8 cm(3) in controls, p < 0.005). Subjects with Down syndrome had a smaller mid- and lower face skeleton. They had a shorter mental spine-clivus distance (5.7 +/- 0.6 versus 6.2 +/- 0.4 cm, p < 0.05), hard palate length (3.2 +/- 0.4 versus 3.7 +/- 0.2 cm, p < 0.005), and mandible volume (11.5 +/- 3.7 versus 16.9 +/- 2.9 cm3, p < 0.0005). Adenoid and tonsil volume was significantly smaller in the subjects with Down syndrome. However, the tongue, soft-palate, pterygoid, and parapharyngeal fat pads were similar to those of control subjects. This study shows that Down syndrome children without OSA do not have increased adenoid or tonsillar volume; reduced upper airway size is caused by soft tissue crowding within a smaller mid- and lower face skeleton.

Fractal analysis of eye movements during reading.

We present a new method for the analysis of reading eye movements based on the methods of nonlinear dynamics. In this preliminary study, the eye movements of normal and abnormal readers were analyzed for evidence of chaotic, nonlinear dynamical behavior. Both power spectral density analysis and fractal dimension determination showed evidence of nonlinearity as manifest in chaotic behavior. The computed fractal dimension of the system's presumed attractor seemed directly related to qualitative assessment of reading ability. Representative subjects did not differ in a similar analysis of pursuit movements. Although fractal analysis did not distinguish unconditionally between normal and abnormal reading in this preliminary study, it nevertheless offers a promising hitherto unused approach to the analysis of eye movements and the modeling of oculomotor behavior.

Altered lung mechanics after double-lung transplantation.

We studied lung mechanics and small airways function in 15 patients after double-lung (DL) transplantation. Patients were classified as stable (DL-S, n = 11), or having obliterative bronchiolitis syndrome (DL-OBS, n = 4). We performed pulmonary function tests (PFT), measured slope of phase 3 of the single-breath nitrogen test (N2SP3), and obtained pressure-volume curves and values: chord compliance (Cst,L), specific chord compliance (SCst,L), and elastic recoil pressure at 90% TLC. PFT showed mild restrictive pattern in DL-S and severe obstructive lung disease in DL-OBS. The N2SP3 measurement indicated small airways dysfunction in 82% of DL-S and in all DL-OBS patients. The Cst,L was 0.24 +/- 0.08 L/cm H2O in DL-S and 0.16 +/- 0.05 L/cm H2O in DL-OBS, both lower than control subjects 0.34 +/- 0. 09 L/cm H2O (p < 0.01; p < 0.001). Moreover, SCst,L was 0.09 +/- 0. 03 cm H2O-1 in DL-S, and 0.05 +/- 0.02 cm H2O-1 in DL-OBS, significantly lower than control subjects 0.12 +/- 0.02 cm H2O-1 (p < 0.05; p < 0.001). Elastic recoil at 90% TLC was normal in 14 of 15 patients. We found a linear correlation between N2SP3 and FEV1, and between FEV1 and Cst,L and SCst,L for combined DL-S and DL-OBS. Reduced compliance near FRC with normal elastic recoil at high lung volumes does not suggest changes in lung parenchyma. We speculate that structural or functional alterations in small airways may have contributed to low compliance measurements. Of special concern are our findings that DL-S had significant small airways dysfunction and reduced compliance in a pattern similar to the DL-OBS, only smaller in magnitude.

Effects of positive end-expiratory pressure on lung tissue mechanics in rabbits.

The effects of positive end-expiratory pressure (PEEP) on lung tissue resistance (Rti) and dynamic elastance (Edyn,L) were examined separately during histamine-induced lung constriction and after saline lung lavage in anesthetized paralyzed New Zealand White rabbits. During mechanical ventilation in the open-chest state, Rti and Edyn,L were estimated by fitting the appropriate signals to the equation of motion of the single-compartment linear model of the lung. Data were analyzed in relation to the structural damping hypothesis, which assumes that energy dissipation (Rti) and energy storage (Edyn,L) within the lung tissues are coupled at a fundamental level; the coupling parameter, termed hysteresivity (eta), = Rti.omega/Edyn,L, where omega is angular frequency. Under baseline conditions, elevation in PEEP resulted in significant increases in both Rti and Edyn,L, with eta remaining unchanged. During induced constriction and after lung lavage, Rti and Edyn,L significantly increased relative to their baseline values. During histamine-induced constriction, increasing PEEP was associated with increases in Edyn,L, whereas Rti and eta were reduced. After lung lavage, elevation in PEEP from 5 to 7 cmH2O was associated with proportional increases in Rti and Edyn,L, resulting in a relative constancy of eta. By contrast, when PEEP was decreased from 5 to 3 cmH2O, the values of Rti increased, whereas Edyn,L remained unchanged, resulting in significant increases in eta. Collectively, these findings suggest that the effects of PEEP on Rti during agonist-induced constriction and after perturbations of the gas-liquid interface are dependent on the state of alveolar/airway stability.

Effect of helium concentration on experimental upper airway obstruction.

This study investigates the effect of helium concentration in inspired gas on resistance to breathing during experimental upper airway obstruction. Obstruction was modeled by use of a series of four polyvinyl endotracheal tubes narrowed progressively in their midportions with C clamps. Percentage ratios of helium-oxygen gas mixtures were 0:100, 40:60, 60:40, and 80:20. Gas flow was provided by two methods: 1) nontidal flow from compressed gas tanks from which resistance was calculated from pressure and flow measurements, and 2) tidal respiratory flow from human volunteers from whom respiratory effort was evaluated by using airway pressure measurements integrated over 90-second trial periods. The results derived from both methods demonstrated that the effect of helium in reducing resistance and pressure in an obstructed airway is linear (p less than .016) and inversely proportional to helium concentration. Reductions in resistance and pressure were larger for the tighter obstructions (p less than .007). As helium was added to the gas mixture (from 0% to 80%), resistance and airway pressure measurements dropped 42% and 58%, respectively. The major conclusions are that 1) even low concentrations of helium may have therapeutic value and 2) helium is effective only for more severe obstructions.

Histopathology in the rainbow darter, Etheostoma caeruleum, resulting from infections with the Acanthocephalans, Pomphorhynchus bulbocolli and Acanthocephalus dirus.

The histopathology present in Etheostoma caeruleum naturally infected with the acanthocephalans, Acanthocephalus dirus and Pomphorhynchus bulbocolli, was studied and described. The major difference in parasite-induced histopathology was related to the shallow penetration of A. dirus proboscides in the intestinal wall as compared to the penetration of P. bulbocolli. The host responded to the presence of the parasites with connective tissue hyperplasia and with an infiltration of leukocytes, predominantly lymphocytes and eosinophilic granulocytes. The response was greater to P. bulbocolli than to A. dirus. The complete penetration of the intestinal wall by the proboscis, bulb, and neck of P. bulbocolli elicited an intense host response. This resulted in the formation of a tunnel around the neck and capsule around the bulb and proboscis of the parasite. Damage to the epithelial lining of the intestine occurred in areas of contact with the trunk of the parasites. Concurrent infections were common, but there did not appear to be a synergistic effect as a result of the presence of both parasites.

Reconstruction of the breast after mastectomy.

We have described our techniques for reconstruction of the breast after a simple mastectomy, a modified radical mastectomy, and a radical mastectomy. Inadequate skin cover must be relieved, preferably by transposition of a thoracoepigastric flap. Not only must a mound be created, but also a nipple-areola complex. The areola can be constructed by nipple-sharing techniques from the opposite breast or by the use of the labia minora and/or the labia majora. However, we advise preservation and banking of the nipple-areola (or areola) by the ablative surgeon, when possible. The remaining breast usually requires some modification to match the reconstructed one.

The veterans administration and community mental health: New approaches in psychiatric rehabilitation.

The large government mental institution must become increasingly integrated with local community mental health programs. The Veterans Administration Hospital, Palo Alto, California, provides an example of how one such institution involves its programs with the community. The traditional hospital-based sheltered workshop, when operated as a nonprofit corporation, is especially well suited to the employment of mental patients in workshop-owned enterprises outside the hospital walls. The flexibility of the program is illustrated with case histories. Advantages to the client, the institution, and the community are discussed.