Can pulsatile CSF flow across the cerebral aqueduct cause ventriculomegaly? A prospective study of patients with communicating hydrocephalus.

BACKGROUND: Communicating hydrocephalus is a disease where the cerebral ventricles are enlarged. It is characterized by the absence of detectable cerebrospinal fluid (CSF) outflow obstructions and often with increased CSF pulsatility measured in the cerebral aqueduct (CA). We hypothesize that the cardiac-related pulsatile flow over the CA, with fast systolic outflow and slow diastolic inflow, can generate net pressure effects that could source the ventriculomegaly in these patients. This would require a non-zero cardiac cycle averaged net pressure difference (ΔPnet) over the CA, with higher average pressure in the lateral and third ventricles. METHODS: We tested the hypothesis by calculating ΔPnet across the CA using computational fluid dynamics based on prospectively collected high-resolution structural (FIESTA-C, resolution 0.39 × 0.39 × 0.3 mm3) and velocimetric (2D-PCMRI, in-plane resolution 0.35 × 0.35 mm2) MRI-data from 30 patients investigated for communicating hydrocephalus. RESULTS: The ΔPnet due to CSF pulsations was non-zero for the study group (p = 0.03) with a magnitude of 0.2 ± 0.4 Pa (0.001 ± 0.003 mmHg), with higher pressure in the third ventricle. The maximum pressure difference over the cardiac cycle ΔPmax was 20.3 ± 11.8 Pa and occurred during systole. A generalized linear model verified an association between ΔPnet and CA cross-sectional area (p = 0.01) and flow asymmetry, described by the ratio of maximum inflow/outflow (p = 0.04), but not for aqueductal stroke volume (p = 0.35). CONCLUSIONS: The results supported the hypothesis with respect to the direction of ΔPnet, although the magnitude was low. Thus, although the pulsations may generate a pressure difference across the CA it is likely too small to explain the ventriculomegaly in communicating hydrocephalus.

Venous collapse regulates intracranial pressure in upright body positions.

Recent interest in intracranial pressure (ICP) in the upright posture has revealed that the mechanisms regulating postural changes in ICP are not fully understood. We have suggested an explanatory model where the postural changes in ICP depend on well-established hydrostatic effects in the venous system and where these effects are interrupted by collapse of the internal jugular veins (IJVs) in more upright positions. The aim of this study was to investigate this relationship by simultaneous invasive measurements of ICP, venous pressure, and IJV collapse in healthy volunteers. ICP (monitored via the lumbar route), central venous pressure (peripherally inserted central catheter line), and IJV cross-sectional area (ultrasound) were measured in 11 healthy volunteers (47 ± 10 yr, mean ± SD) in 7 positions, from supine to sitting (0-69°). Venous pressure and anatomical distances were used to predict ICP in accordance with the explanatory model, and IJV area was used to assess IJV collapse. The hypothesis was tested by comparing measured ICP with predicted ICP. Our model accurately described the general behavior of the observed postural ICP changes (mean difference, -0.03 ± 2.7 mmHg). No difference was found between predicted and measured ICP for any tilt angle ( P values, 0.65-0.94). The results support the hypothesis that postural ICP changes are governed by hydrostatic effects in the venous system and IJV collapse. This improved understanding of postural ICP regulation may have important implications for the development of better treatments for neurological and neurosurgical conditions affecting ICP.

Effect of vibration magnitude, vibration spectrum and muscle tension on apparent mass and cross axis transfer functions during whole-body vibration exposure.

Twelve seated male subjects were exposed to 15 vibration conditions to investigate the nature and mechanisms of the non-linearity in biomechanical response. Subjects were exposed to three groups of stimuli: Group A comprised three repeats of random vertical vibration at 0.5, 1.0 and 1.5 ms(-2) r.m.s. with subjects sitting in a relaxed upright posture. Group B used the same vibration stimuli as Group A, but with subjects sitting in a 'tense' posture. Group C used vibration where the vibration spectrum was dominated by either low-frequency motion (2-7 Hz), high-frequency motion (7-20 Hz) or a 1.0 ms(-2) r.m.s. sinusoid at the frequency of the second peak in apparent mass (about 10-14 Hz) added to 0.5 ms(-2) r.m.s. random vibration. In the relaxed posture, frequencies of the primary peak in apparent mass decreased with increased vibration magnitude. In the tense posture, the extent of the non-linearity was reduced. For the low-frequency dominated stimulus, the primary peak frequency was lower than that for the high-frequency dominated stimulus indicating that the frequency of the primary peak in the apparent mass is dominated by the magnitude of the vibration encompassing the peak. Cross-axis transfer functions showed peaks of about 15-20% and 5% of the magnitudes of the peaks in the apparent mass for x- and y-direction transfer functions, respectively, in the relaxed posture. In the tense posture, cross-axis transfer functions reduced in magnitude with increased vibration, likely indicating a reduced fore-aft pitching of the body with increased tension, supporting the hypothesis that pitching contributes to the non-linearity in apparent mass.

Mechanical impedance of the sitting human body in single-axis compared to multi-axis whole-body vibration exposure.

OBJECTIVE: The study was aimed to investigate the mechanical impedance of the sitting human body and to compare data obtained in laboratory single-axis investigations with multi-axis data from in vehicle measurements. DESIGN: The experiments were performed in a laboratory for single-axis measurements. The multi-axis exposure was generated with an eight-seat minibus where the rear seats had been replaced with a rigid one. The subjects in the multi-axis experiment all participated in the single-axis experiments. BACKGROUND: There are quite a few investigations in the literature describing the human response to single-axis exposure. The response from the human body can be expected to be affected by multi-axis input in a different way than from a single-axis exposure. The present knowledge of the effect of multiple axis exposure is very limited. METHODS: The measurements were performed using a specially designed force and accelerometer plate. This plate was placed between the subject and the hard seat. RESULTS: Outcome shows a clear difference between mechanical impedance for multi-axis exposure compared to single-axis. This is especially clear in the x-direction where the difference is very large. CONCLUSIONS: The conclusion is that it seems unlikely that single-axis mechanical impedance data can be directly transferred to a multi-axis environment. This is due to the force cross-talk between different directions.

Mechanical impedance of the human body in vertical direction.

The mechanical impedance of the human body in sitting posture and vertical direction was measured during different experimental conditions, such as vibration level (0.5-1.4 m/s2), frequency (2-100 Hz), body weight (57-92 kg), relaxed and erect upper body posture. The outcome shows that impedance increases with frequency up to a peak at about 5 Hz after which it decreases in a complex manner which includes two additional peaks. The frequency at which the first and second impedance peak occurs decreases with higher vibration level. Erect, compared with relaxed body posture resulted in higher impedance magnitudes and with peaks located at somewhat higher frequencies. Heavy persons show higher impedance magnitudes and peaks at lower frequencies.

Immobilization of a biologically active coating on a hydrophobic L-lactide-epsilon-caprolactone copolymer.

The electron beam radiation induced grafting method was used to attach a reactive polyacrylamide (PAA) layer (20 wt %) on the surface of a biodegradable poly-L-lactide-co-epsilon-caprolactone (PLLA-co-CL). The biocompatibility of graft-polymer obtained was studied by cytotoxicity test and no signs of toxicity were observed. Heparin and sol-gel-produced silica-gel coatings were successfully attached on the top of the polymeric material produced. The amount of heparin immobilized directly on the surface can be controlled by reaction conditions: reaction time, temperature and pH of the incubation solution. By using acidic conditions, up to 98 microg cm(-2) of heparin was immobilized on the surface. The sol-gel-produced silica-gel layer formed by dipping technique was 30 microm thick and the cracking of the layer was minimal after bending several times to 90 degrees.

Absorption of energy during vertical whole-body vibration exposure.

Absorbed power (PAbs) during exposure to vertical whole-body vibration in a sitting posture was measured on 15 male and 15 female subjects. Different experimental conditions were applied, such as vibration level (0.5-1.4 m s(-2)) and frequency (2-100 Hz), body weight (54-93 kg) and, relaxed and erected upper body positions. Results show that PAbs was strongly related to the frequency of the vibration, peaking within the range of 4-6 Hz. The peak was predominantly located in the lower end of this range for females and for the relaxed sitting position. PAbs increased with acceleration level and body weight. Almost a ten-fold increase in PAbs was observed at the critical frequency when the vibration exposure was raised from 0.5 to 1.4 m s(-2). If risk assessment is based on the assumption that the amount of PAbs, independent of the frequency of the vibration, indicates a hazard, then the ISO-standard 2631 under- and overestimates the risk at frequencies below and above about 6 Hz, respectively. The results also indicate a need for differentiated guidelines for females and males. Many types of vehicles produce whole-body vibration with frequencies which coincide with the range where the highest PAbs was observed. PAbs is a 'new' concept for measurement of whole-body vibration exposure. Although not yet thoroughly evaluated, this measure may be a better quantity for risk assessment than those specified in ISO 2631 since it also takes the dynamic force applied to the human body into account.

Some effects of 1-(2,4-Dichlorophenyl)-4-dimethylamino-methyl-1-nonen-3-one hydrochloride on Escherichia coli GK-19.

1-(2,4-Dichlorophenyl)-4-dimethylaminomethyl-1-nonen-3-one hydrochloride (Id) was shown to inhibit the growth of Escherichia coli GK-19 at a concentration of 50 micrograms/mL in a medium of pH 6.5. Maximal antibacterial activity was found during the logarithmic growth phases rather than at the early stationary phase. Electron microscopy revealed that Id caused lysis, and inhibition of respiration and retardation of RNA and protein syntheses occurred in the bacteria with this compound at 50 micrograms/mL.