Equiintensity contours of photometric patterns of focused linearly polarized light (650 nm) were fitted with ellipses that appeared to follow the orientation of collagen fibers. The ratio of the ellipses semi-axes is well correlated with the ratio of reduced scattering coefficients obtained from intensity profiles. The mapping of the polarization degree shown that for skin and collagen based phantom it may preserved up to 1.5-2.5 mm distance from the probe beam injection.

To investigate the pathophysiology of syringomyelia, we developed a system to simultaneously record arterial, central venous, airway, cervical subarachnoid and intrathecal pressures. In addition, our system records electrocardiograms (ECGs) and provides us with the means to analyze all pressures during individual and averaged cardiac cycles. During the described study, flow magnetic resonance imaging and cardiac-gated ultrasound images were also used. To compare our pressure readings with these images, we needed to account for the low-frequency changes in the recorded pressures resulting from normal respiration. We therefore wrote a program to derive mean pressure waves during the cardiac cycle that averaged out the pressure effects of the respiratory cycle. Simultaneous cerebrospinal pressure, hemodynamic pressure and ECG were plotted. This allowed us to establish the simultaneous relationship between pressures, syrinx size and cerebellar tonsil pulsation during the cardiac cycle. This system may prove valuable to other researchers investigating the interactions between multiple physiological parameters during the cardiac cycle

Ibuprofen has been shown in vitro to modulate production of nitric oxide (NO), a mediator of sepsis-induced hypotension. We sought to determine whether ibuprofen alters NO production and, thereby, vascular tone, in normal and endotoxin-challenged volunteers. Techniques for detecting NO were validated in 17 subjects infused with sodium nitroprusside, a NO donor. Then, endotoxin (4 ng/kg) or saline (vehicle alone) was administered in a single-blinded, crossover design to 12 other subjects randomized to receive either ibuprofen (2400 mg p.o.) or a placebo. Endotoxin decreased mean arterial pressure (MAP; P =.002) and increased alveolar NO flow rates (P =.04) and urinary excretion of nitrite and nitrate (P =.07). In both endotoxemic and normal subjects, ibuprofen blunted the small fall in MAP associated with bed rest (P =.005) and decreased alveolar NO flow rates (P =.03) and urinary excretion of nitrite and nitrate (P =.02). However, ibuprofen had no effect on the decrease in MAP caused by endotoxin, although it blocked NO production to the point of disrupting the normal relationship between increases in exhaled NO flow rate and decreases in MAP (P =.002). These are the first in vivo data to demonstrate that ibuprofen down-regulates NO in humans. Ibuprofen impaired the NO response to bed rest, producing a small rise in blood pressure. Although ibuprofen also interfered with the ability of endotoxin to induce NO production, it had no effect on the fall in blood pressure, suggesting that the hemodynamic response to endotoxin is not completely dependent on NO under these conditions.

OBJECT Syringomyelia causes progressive myelopathy. Most patients with syringomyelia have a Chiari I malformation of the cerebellar tonsils. Determination of the pathophysiological mechanisms underlying the progression of syringomyelia associated with the Chiari I malformation should improve strategies to halt progression of myelopathy. METHODS The authors prospectively studied 20 adult patients with both Chiari I malformation and symptomatic syringomyelia. Testing before surgery included the following: clinical examination; evaluation of anatomy by using T1-weighted magnetic resonance (MR) imaging; evaluation of the syrinx and cerebrospinal fluid (CSF) velocity and flow by using phase-contrast cine MR imaging; and evaluation of lumbar and cervical subarachnoid pressure at rest, during the Valsalva maneuver, during jugular compression, and following removal of CSF (CSF compliance measurement). During surgery, cardiac-gated ultrasonography and pressure measurements were obtained from the intracranial, cervical subarachnoid, and lumbar intrathecal spaces and syrinx. Six months after surgery, clinical examinations, MR imaging studies, and CSF pressure recordings were repeated. Clinical examinations and MR imaging studies were repeated annually. For comparison, 18 healthy volunteers underwent T1-weighted MR imaging, cine MR imaging, and cervical and lumbar subarachnoid pressure testing. Compared with healthy volunteers, before surgery, the patients had decreased anteroposterior diameters of the ventral and dorsal CSF spaces at the foramen magnum. In patients, CSF velocity at the foramen magnum was increased, but CSF flow was reduced. Transmission of intracranial pressure across the foramen magnum to the spinal subarachnoid space in response to jugular compression was partially obstructed. Spinal CSF compliance was reduced, whereas cervical subarachnoid pressure and pulse pressure were increased. Syrinx fluid flowed inferiorly during systole and superiorly during diastole on cine MR imaging. At surgery, the cerebellar tonsils abruptly descended during systole and ascended during diastole, and the upper pole of the syrinx contracted in a manner synchronous with tonsillar descent and with the peak systolic cervical subarachnoid pressure wave. Following surgery, the diameter of the CSF passages at the foramen magnum increased compared with preoperative values, and the maximum flow rate of CSF across the foramen magnum during systole increased. Transmission of pressure across the foramen magnum to the spinal subarachnoid space in response to jugular compression was normal and cervical subarachnoid mean pressure and pulse pressure decreased to normal. The maximum syrinx diameter decreased on MR imaging in all patients. Cine MR imaging documented reduced velocity and flow of the syrinx fluid. Clinical symptoms and signs improved or remained stable in all patients, and the tonsils resumed a normal shape. CONCLUSIONS The progression of syringomyelia associated with Chiari I malformation is produced by the action of the cerebellar tonsils, which partially occlude the subarachnoid space at the foramen magnum and act as a piston on the partially enclosed spinal subarachnoid space. This creates enlarged cervical subarachnoid pressure waves that compress the spinal cord from without, not from within, and propagate syrinx fluid caudally with each heartbeat, which leads to syrinx progression. The disappearance of the abnormal shape and position of the tonsils after simple decompressive extraarachnoidal surgery suggests that the Chiari I malformation of the cerebellar tonsils is acquired, not congenital. Surgery limited to suboccipital craniectomy, C-I laminectomy, and duraplasty eliminates this mechanism and eliminates syringomyelia and its progression without the risk of more invasive procedures.

We have reported that low frequency stimulation (1 Hz for 15 min), applied after kindling stimulation of the amygdala, inhibited the development and expression of amygdala-kindled seizures, an effect we termed quenching. Subsequently, we discovered that this effect could only be achieved when certain stimulators were used that also emitted a low-level direct current (DC). The studies reported here indicate that DC, applied once daily for 15 min at intensities of 5-15 microA, produced an intensity-related attenuation of kindling development and an increase in the afterdischarge threshold. This effect persisted in some animals for at least 1 month after discontinuation of the DC. In fully kindled animals, a robust increase in seizure threshold and persistent seizure inhibition were also observed using 10 microA of DC administered for 14 days. These results clarify and extend our original findings of a quenching effect; however, the mechanisms by which low level DC induces quenching require further elucidation.

Objective: To determine whether human endotoxemia is associated with a loss of the physiologic beat-to beat variability of heart rate,Design: Prospective, randomized, crossover, single blind study, Setting: Clinical research center in a federal, nonuniversity hospital,Subjects: Healthy volunteers,Interventions,, Intravenous administration of reference (Escherichia coli) endotoxin or saline placebo, with or without previous administration of oral ibuprofen,Measurements and Main Results: Electrocardiograms were continuously recorded and digitized using series of 1000 beat epochs of R-R intervals over 8 hrs, Analyses included measures in the time domain (standard deviation), frequency domain (power spectra), and a measure of regularity (approximate entropy), Endotoxin administration was associated with loss of variability by all measures, This loss of variability remained significant even with administration of ibuprofen, which blocked the development of fever and endotoxin related symptoms. Conclusions: Infusion of endotoxin into human volunteers causes loss of heart rate variability, as measured by standard deviation and power spectra, as well as an increase in heart rate regularity, as measured by approximate entropy, Changes in ap proximate entropy occurred earlier than changes in other heart rate variability measures and may be a useful means of detecting early sepsis, This reduction in regularity is consistent with a model in which the pathogenesis of multiple organ system dysfunction syndrome involves the physiologic uncoupling of vital organ systems.