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PubMed2005

Gravitational artifact in accelerometric measurements of tremor.

OBJECTIVE: To illustrate the problem of gravitational artifact in accelerometric recordings of tremor. METHODS: Gravitational and inertial accelerations were computed for a triaxial accelerometer that was attached to a hand, oscillating vertically about the wrist. Mathematical equations for hand motion were solved with commercial software. RESULTS: Accelerometer output contains proportionately larger gravitational artifact at lower frequencies of oscillation and when the accelerometer is mounted closer to the wrist. A vertical accelerometer axis contains nearly constant gravitational artifact when the amplitude of wrist oscillation is less than +/-20 degrees. Proportionately large gravitational artifact can occur in accelerometer axes that are perpendicular to the path of motion. Gravitational and inertial oscillations at twice the frequency of wrist oscillation emerge from the equations of motion. CONCLUSIONS: When the hand is horizontal, the vertical accelerometer axis contains nearly constant gravitational artifact during the recording of most tremors, and high-pass filtering effectively removes this artifact. Gravitational artifact is more problematic when the hand is vertical, as during the measurement of Parkinson rest tremor, particularly if the accelerometer is mounted close to the wrist. SIGNIFICANCE: Two accelerometers, mounted in parallel, are needed to capture hand rotation in a single plane of motion, free of gravitational artifact.

Acceleration↗
PubMed1991

Gravitational fields and aging.

Alteration of the ambient gravitational field and aging are both accompanied by a variety of physiological changes, but at present it is not possible to estimate how aging and alteration of gravitational fields would interact. The time will undoubtedly come when it will be advantageous to expose individuals of older ages to the altered gravitational fields. Consequently it is timely to know in advance the limitations and special maintenance requirements, if any, that may apply. The importance of such studies has been recognized by Comfort (3) in a chapter entitled "A special application: Aerospace Gerontology." Initially there should be a series of experiments in which animals of increasing ages are exposed to the weightlessness of spaceflight, and to increased fields provided by centrifugation. Also of interest would be the study of the effects of long-term exposure to moderately increased acceleration fields (1/2-1 G) to determine the gravitational effects on the aging process. In addition to its application toward improving the maintenance of aging astronauts/cosmonauts, such information also should contribute to the general understanding of gravitational physiology. Conversely, the effects exposure to the unconventional stress of altered gravitational fields, and the nature of any counter-measure developed, would be valuable contributions to the understanding of aging and the management of the elderly. It appears only logical that at least as much attention be given to gravitational fields and aging, as is given to gravitational fields and development.

Adult↗
PubMed2005

Effect of gravitational force on type-J counter-current chromatography by mathematical analysis.

The gravitational force exerts an important effect on the counter-current chromatography (CCC) and has been used to retain the stationary phase and improve the efficiency in the various CCC separations. This paper deals with the effect of gravitational force on type-J CCC, one of the most popular CCC methods by the mathematical analysis for the first time. The theoretical analyses reveal a close relationship between the effect of gravitational force, the placed orientation of type-J CCC apparatus, and the revolutional speed. Two placed orientations are more suitable for preparative CCC separation: one is common horizontal, and the other upright. Thus, there are three optimum conditions for type-J CCC separation, the first using horizontal apparatus at very low revolutional speed around 10rpm in the gravitational filed, the second by use of upright apparatus at moderate revolutional speed around 100rpm in the three-dimensional complex force field composed of centrifugal and orthogonal gravitational force, and the third employing the apparatus placed at any orientation including horizontal and upright CCC apparatus at high revolutional speed above 300rpm in the centrifugal force field. Therefore, we should consider the effect of gravitation force on CCC at the selection of proper operational conditions according to properties of two immiscible phases, the desired revolutional speed and the parameters of apparatus in order to utilize efficiently the effect of gravitational force. These analyses and results will benefit to improve the efficiency of CCC separation, especially large-scale industrial preparation.

Countercurrent Distribution↗
PubMed2004

Gravitational effects on the weld pool shape and microstructural evolution during gas tungsten arc and laser beam welding of 304 stainless steel and Al-4 wt% Cu alloy.

Effects of gravitational acceleration were investigated on the weld pool shape and microstructural evolution for 304 stainless steel and Al-4wt% Cu alloy. Effects of welding heat source were investigated by using laser beam welding (LBW) and gas tungsten arc welding (GTAW). As the gravitational level was increased from low gravity (LG approximately 1.2 g) to high gravity (HG approximately 1.8 g) using a NASA KC-135 aircraft, the weld pool shape for 304 stainless steel was influenced considerably during GTAW. However, insignificant change in the microstructure and solute distribution was observed at gravitational levels between LG and HG. The GTAW on Al-4 wt% Cu alloy was used to investigate the effect of gravitational orientation on the weld solidification behavior. Gravitational orientation was manipulated by varying the welding direction with respect to gravity vector; that is, by welding upward opposing gravity ( ||-U) and downward with gravity ( ||-D) on a vertical weld piece and welding perpendicular to gravity (perpendicular) on a horizontal weld piece. Under the same welding conditions, a larger primary dendrite spacing in the ||-U weld was observed near the weld pool surface and the fusion boundary than in the case of perpendicular or ||-D welds. The ||-D weld exhibited different solidification morphology and abnormal S shape of solidification rate curve during its growth. For 304 stainless steel GTAW, significant effects of gravitational orientation were observed on the weld pool shape that was associated with weld surface morphology and convection flow. However, the weld pool shape for LBW was mostly constant with respect to the gravitational orientation.

Alloys↗
PubMed1986

A relative thrombocytosis and elevated mean platelet volume are features of gravitational disease.

Platelet counts were obtained in 60 patients with gravitational ulceration (GU), 60 with gravitational eczema (GE), 56 with endogenous eczema (EE) and 60 normal controls. Mean platelet volume (MPV), a broad index of platelet size, was estimated in the last 40 patients in each group (29 with EE). Causes of a reactive thrombocytosis were excluded. Platelet counts were significantly higher in both gravitational groups than in the EE group or the normal controls (P = 0.001). Ulcer healing produced no significant changes in platelet count, and patients with non-gravitational ulcers had normal platelet counts. MPV was significantly higher in both gravitational groups than in controls after correction for platelet count, by analysis of co-variance (P = 0.01). These differences in platelet parameters in gravitational disease suggest a possible role for platelets in this disease, and platelet inhibiting therapy may be of value at an early stage in the development of the condition.

Adult↗
PubMed1991

Gravitational forces on the chest wall.

The gravitational work of breathing was determined by measuring the vertical motion of body mass. The subject, seated or lying supine on a force platform, performed breathing maneuvers in which rib cage volume (Vrc) and abdominal volume (Vab) were changed in varying proportions. The increment in the vertical force exerted on the platform and Vrc and Vab were measured over the course of each maneuver. The force signal was integrated twice with respect to time to obtain the change in the product of mass and height of the subject. This was multiplied by the gravitational acceleration to obtain the change in the gravitational potential (Ug). Simultaneous values of Ug, Vrc, and Vab were taken from the data, and the values of the coefficients for which the following equation best fit these values were determined: Ug = a1 Vrc + a2 Vab + (1/2)a11 Vrc2 + a12 Vrc Vab + (1/2)a22 Vab2. The coefficients a1 and a2 can be interpreted as the values of the expiratory gravitational forces on the rib cage and abdomen, respectively. In the seated posture, the force on the rib cage is expiratory and the force on the abdomen is inspiratory; the magnitudes of both are approximately 8 cmH2O. In the supine posture, both are expiratory forces of approximately 9 cmH2O. The coefficients of the quadratic terms in Ug are all positive, and the gravitational work per unit volume of chest wall expansion increases with increasing volume in both postures. The coefficients of the quadratic terms can be interpreted as gravitational contributions to the elastances of the compartments.

Acceleration↗
PubMed2000

Invited review: gravitational biology of the neuromotor systems: a perspective to the next era.

Earth's gravity has had a significant impact on the designs of the neuromotor systems that have evolved. Early indications are that gravity also plays a key role in the ontogenesis of some of these design features. The purpose of the present review is not to assess and interpret a body of knowledge in the usual sense of a review but to look ahead, given some of the general concepts that have evolved and observations made to date, which can guide our future approach to gravitational biology. We are now approaching an era in gravitational biology during which well-controlled experiments can be conducted for sustained periods in a microgravity environment. Thus it is now possible to study in greater detail the role of gravity in phylogenesis and ontogenesis. Experiments can range from those conducted on the simplest levels of organization of the components that comprise the neuromotor system to those conducted on the whole organism. Generally, the impact of Earth's gravitational environment on living systems becomes more complex as the level of integration of the biological phenomenon of interest increases. Studies of the effects of gravitational vectors on neuromotor systems have and should continue to provide unique insight into these mechanisms that control and maintain neural control systems designed to function in Earth's gravitational environment. A number of examples are given of how a gravitational biology perspective can lead to a clearer understanding of neuromotor disorders. Furthermore, the technologies developed for spaceflight studies have contributed and should continue to contribute to studies of motor dysfunctions, such as spinal cord injury and stroke. Disorders associated with energy support and delivery systems and how these functions are altered by sedentary life styles at 1 G and by space travel in a microgravity environment are also discussed.

Animals↗
PubMed2002

Five years experience with gravitational shunts in chronic hydrocephalus of adults.

OBJECTIVE: Gravitational shunts for management of chronic hydrocephalus are supposed to avoid or at least to reduce the risk of overdrainage. In order to find out if this hypothesis is correct, we did a prospective study and analysed the results of a series of 185 hydrocephalic adults, treated by using gravitational shunts. For the few cases in whom overdrainage occurred, we wanted to establish the reason for it. Especially it should be proven or excluded that overdrainage was caused by shortcomings of the principle of gravitational shunts. Another goal was to compare post-shunting changes of the ventricular size with clinical outcome. A comparably large study has not yet been published. METHODS: 185 adult patients who suffered from chronic hydrocephalus were shunted between 1996-2000, either using the combination of an adjustable Codmann Hakim Valve & Miethke Shunt Assistant (35 patients) or a Miethke Dual Switch Valve (150 patients). The clinical course of each patient has been followed until the end of 2000. Average follow-up time was 26 months (range 6-60 months). RESULTS: 88% of our patients were shunt responders, 70% had a good or excellent outcome. Overdrainage occurred in only 4%. It turned out that this complication was not a failure of the concept of gravitational shunts, but the result of a wrongly estimated intraperitoneal pressure. After shunting the ventricular size was reduced only marginally. In 92% of the patients the Evans-Index decreased less than 20% after the shunt insertion, but 69% of these patients had a good or excellent outcome. The most obvious difference comparing pre- and postoperative imaging was a better visibility of the high apical sulci after shunting. CONCLUSION: In our series gravitational shunts proved to be effective in preventing overdrainage. The 4% negative exceptions are mainly avoidable. There was no correlation between outcome and ventricular size reduction, and as a rule ventricular size was only marginally reduced.

Aged↗
PubMed2000

Different elution modes and field programming in gravitational field-flow fractionation. 2. Experimental verification of the range of conditions for flow-rate and carrier liquid density programming.

Gravitational field-flow fractionation utilises the Earth's gravitational field as an external force that causes the settlement of particles towards the channel accumulation wall. Hydrodynamic lift forces oppose this action by elevating of particles from the channel accumulation wall. Therefore there are several possibilities to modulate the resulting force field acting on particles in gravitational field-flow fractionation. Regarding the force field programming in gravitational field-flow fractionation, this work focused on two topics: changes of the difference between particle density and carrier liquid density in Brownian and focusing elution modes and influencing of lift forces achieved by changing the flow-rate in focusing elution mode. We have found and described the experimental conditions applicable to force field programming in the case of separations of silica gel particles by gravitational field-flow fractionation. It was shown that the effect of carrier liquid viscosity in the water-methanol system is implemented as an additional factor enhancing the desired effect of carrier liquid density. Some other forces influencing the retention behaviour of the model particles are discussed.

Chemical Fractionation↗
PubMed1998

Distraction of lumbar vertebrae in gravitational traction.

STUDY DESIGN: Experimental study of 30 patients diagnosed with low back pain resulting from lumbar disc herniation, disc degeneration, and segmental instability. Patients underwent gravitational traction, and widening of the intervertebral space and posterior facets was measured on radiographs. This same procedure was performed with a group of 30 healthy individuals. OBJECTIVES: To determine the effect of gravitational traction on the widening of the intervertebral space and the other vertebral structures in patients with low back pain and in healthy individuals. SUMMARY OF BACKGROUND DATA: Gravitational traction is performed by suspending the patient in a hanging, upright position for an extended period of time. In spite of disagreement among authors about the effect of lumbar traction, recent innovations have enabled the distraction of vertebrae. METHODS: A specially designed apparatus was used to apply gravitational traction. Pre- and post-traction radiographs were obtained to study the changes in the L2-L3, L3-L4, L4-L5, and L5-S1 intervertebral spaces; Ferguson's angle; L1-S1 total distance; and blood pressure. RESULTS: Distraction was more than approximately 3 mm in each intervertebral space in both groups. CONCLUSION: Gravitational traction had a very apparent effect on intervertebral space and was found to be an effective method to distract lumbar vertebrae. Discomfort experienced by the patient during suspension may be overcome by making biomedical changes to the suspension corset.

Adult↗