Transmantle Pressure Computed from MR Imaging Measurements of Aqueduct Flow and Dimensions.

BACKGROUND AND PURPOSE: Measuring transmantle pressure, the instantaneous pressure difference between the lateral ventricles and the cranial subarachnoid space, by intracranial pressure sensors has limitations. The aim of this study was to compute transmantle pressure noninvasively with a novel nondimensional fluid mechanics model in volunteers and to identify differences related to age and aqueductal dimensions. MATERIALS AND METHODS: Brain MR images including cardiac-gated 2D phase-contrast MR imaging and fast-spoiled gradient recalled imaging were obtained in 77 volunteers ranging in age from 25-92 years of age. Transmantle pressure was computed during the cardiac cycle with a fluid mechanics model from the measured aqueductal flow rate, stroke volume, aqueductal length and cross-sectional area, and heart rate. Peak pressures during caudal and rostral aqueductal flow were tabulated. The computed transmantle pressure, aqueductal dimensions, and stroke volume were estimated, and the differences due to sex and age were calculated and tested for significance. RESULTS: Peak transmantle pressure was calculated with the nondimensional averaged 14.4 (SD, 6.5) Pa during caudal flow and 6.9 (SD, 2.8) Pa during rostral flow. It did not differ significantly between men and women or correlate significantly with heart rate. Peak transmantle pressure increased with age and correlated with aqueductal dimensions and stroke volume. CONCLUSIONS: The nondimensional fluid mechanics model for computing transmantle pressure detected changes in pressure related to age and aqueductal dimensions. This novel methodology can be easily used to investigate the clinical relevance of the transmantle pressure in normal pressure hydrocephalus, pediatric communicating hydrocephalus, and other CSF disorders.

Subject-Specific Studies of CSF Bulk Flow Patterns in the Spinal Canal: Implications for the Dispersion of Solute Particles in Intrathecal Drug Delivery.

BACKGROUND AND PURPOSE: Recent flow dynamics studies have shown that the eccentricity of the spinal cord affects the magnitude and characteristics of the slow bulk motion of CSF in the spinal subarachnoid space, which is an important variable in solute transport along the spinal canal. The goal of this study was to investigate how anatomic differences among subjects affect this bulk flow. MATERIALS AND METHODS: T2-weighted spinal images were obtained in 4 subjects and repeated in 1 subject after repositioning. CSF velocity was calculated from phase-contrast MR images for 7 equally spaced levels along the length of the spine. This information was input into a 2-time-scale asymptotic analysis of the Navier-Stokes and concentration equations to calculate the short- and long-term CSF flow in the spinal subarachnoid space. Bulk flow streamlines were shown for each subject and position and inspected for differences in patterns. RESULTS: The 4 subjects had variable degrees of lordosis and kyphosis. Repositioning in 1 subject changed the degree of cervical lordosis and thoracic kyphosis. The streamlines of bulk flow show the existence of distinct regions where the fluid particles flow in circular patterns. The location and interconnectivity of these recirculating regions varied among individuals and different positions. CONCLUSIONS: Lordosis, kyphosis, and spinal cord eccentricity in the healthy human spine result in subject-specific patterns of bulk flow recirculating regions. The extent of the interconnectivity of the streamlines among these recirculating regions is fundamental in determining the long-term transport of solute particles along the spinal canal.

Distribution of traction forces associated with shape changes during amoeboid cell migration.

Amoeboid motility results from the cyclic repetition of shape changes leading to periodic oscillations of the cell length (motility cycle). We analyze the dominant modes of shape change and their association to the traction forces exerted on the substrate using Principal Component Analysis (PCA) of time-lapse measurements of cell shape and traction forces in migrating Dictyostelium cells. Using wild-type cells (wt) as reference, we investigated Myosin II activity by studying Myosin II heavy chain null cells (mhcA-) and Myosin II essential light chain null cells (mlcE-). We found that wt, mlcE-and mhcA- cells utilize similar modes of shape changes during their motility cycle, although these shape changes are implemented at a slower pace in Myosin II null mutants. The number of dominant modes of shape changes is surprisingly few with only four modes accounting for 75% of the variance in all cases. The three principal shape modes are dilation/elongation, bending, and bulging of the front/back. The second mode, resulting from sideways protrusion/retraction, is associated to lateral asymmetries in the cell traction forces, and is significantly less important in mhcA- cells. These results indicate that the mechanical cycle of traction stresses and cell shape changes remains remarkably similar for all cell lines but is slowed down when myosin function is lost, probably due to a reduced control on the spatial organization of the traction stresses.