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At least 1,513 records · Page 84Linked to original sources
PubMed1989

The apparent mass of the seated human body: vertical vibration.

Apparent mass frequency response functions of the seated human body have been measured with random vibration in the vertical direction at frequencies up to 20 Hz. A group of eight subjects was used to investigate some factors (footrest, backrest, posture, muscle tension, vibration magnitude) that may affect the apparent mass of a person; a group of 60 subjects (24 men, 24 women and 12 children) was used to investigate variability between people. Relative movement between the feet and the seat was found to affect the apparent mass at frequencies below resonance, particularly near zero-frequency. The resonance frequency generally increased with the use of a back rest, an erect posture and, in particular, increased muscle tension; but there was considerable intersubject variability in the changes. The magnitude of the vibration had a consistent effect: the resonance frequency decreased from about 6 to 4 Hz when the magnitude of the vibration was increased from 0.25 to 2.0 ms-2 r.m.s. The apparent masses of all the subjects were remarkably similar when normalized with respect to sitting weight. However, there were statistically significant correlations between apparent mass and some body characteristics (such as weight and age).

Adolescent↗
PubMed1991

An improved biomechanical model for simulating the strain of the hand-arm system under vibration stress.

In order to define relationships between the vibration stress and the strain of the human hand-arm system a biomechanical model was developed. The four masses of the model representing the hand, the forearm and the upper arm were connected by dampers and springs in two perpendicular directions. Simulating muscle activity, damped torsion springs were included additionally. The motions of the model were described by a differential matrix equation which was solved by using a 'transfer matrix routine' as well as by numerical integration. Thus, functions with harmonic or transient time courses could be selected as an excitation. The simulated vibrations were compared with those of other hand-arm models. The forces and torques transmitted between the masses, and the energy dissipated by the dampers were computed for several combinations of exciter frequencies and accelerations. The dependence of torques upon excitation agreed fairly well with the behaviour of the arm muscles under vibration as described by various investigators. At frequencies above 100 Hz the energy was dissipated mainly by the dampers between the masses near to the exciter. Transferring this result to the hand-arm system it shows that at high frequencies energy is dissipated by the hand and its palmar tissues and this might be one cause for the incidence of vibration-induced white finger disease.

Arm↗
PubMed1995

A data correction method for surface measurement of vibration on the human body.

A data correction method to eliminate the effect of local tissue-accelerometer vibration from surface measurements of vibration over the spine has been developed and compared with previous direct measurements. A single degree-of-freedom linear model for the local tissue-accelerometer system in the vertical and the fore-and-aft axes is assumed. The natural frequency and the damping ratio of the local system are estimated so as to form a correction frequency function, using spectral analysis of the free vibration response of the local system caused by transient displacements of the accelerometer attached to the body surface. Accelerometers were attached to the skin over the spinous process of the vertebra L3 and on the abdominal wall. For four different masses and each site, correction frequency functions were computed. Seated subjects were then exposed to vertical random vibration (0.5-35 Hz) and acceleration transfer functions from the seat to each accelerometer were calculated. Different transfer functions were obtained with different additional masses but the differences were eliminated by the correction method so as to indicate the transfer functions to the spine and the viscera. For vertical responses, the correction method was effective at frequencies below the estimated natural frequencies of the local system. Fore-and-aft response over the spine did not require correction at frequencies below 35 Hz.

Abdominal Muscles↗
PubMed1989

Electrochemical engineering approach to the irrigation of tooth canals under the influence of a vibrating file.

Doubt exists concerning the irrigation of secondary tooth canals when the vibration of a file introduced into the main root canal is superimposed on flow-through irrigation of the main canal. Depending on the type of commercial equipment used, the vibrations of the file are sonic or ultrasonic. We use the methodology of an electrochemical engineering approach in a study of the intensity of the irrigation of the secondary canals under the influence of sonic and ultrasonic vibrations of a file located at various heights in the main canal. The tooth canals are simulated by small electrochemical cells containing electrodes located at the end of cavities simulating the secondary canals. An electrochemical method is used to measure the mass transfer coefficients at these electrodes, a classical method in electrochemical engineering laboratories. The values of the mass transfer coefficients are representative of the importance of the irrigation of the electrodes. Thus they give a quantitative idea of the vibrations on the irrigation of secondary tooth canals. The work demonstrates the usefulness of the electrochemical engineering approach in contributing to the solution of a biomedical problem.

Electrochemistry↗
PubMed1988

Afferent and efferent nerve injury in vibration white fingers.

To study afferent pain and efferent sympathetic nerve function in vibration-induced Raynaud's phenomenon, 10 patients and 11 healthy controls were examined. Thresholds for mechanically and thermally induced pain were determined on the left side of the tip of the second finger, on the skin fold between thumb and second finger and on the ear lobe. Superficial skin blood flow was simultaneously measured by laser Doppler technique on the right third finger. The patients had higher pain thresholds than controls on the vibration-exposed index finger but not on other stimulation areas. Thus receptors or pain-mediating nerve fibres in the fingers are affected by work with vibrating tools. The controls demonstrated vasoconstriction on pain stimulation, whereas the patients showed no or weak vasoconstriction in response to the stimulation. This was true also when areas not included in the disease process were stimulated, indicating that also sympathetic vasoconstrictor nerves or receptors are affected in vibration syndrome.

Afferent Pathways↗
PubMed1980

Incubator noise and vibration--possible iatrogenic influence on neonate.

Analysis of noise and vibration from infant incubators (models Medicor and CN2) revealed average noise levels (peak values) of 60 dB (A-weighted) and 73.5 dB (linear) and values for vibration where the infant's head normally rests were 0.065 m/sec2 (A-weighted) and 0.14 m/sec2 (linear), and at the infants' feet were 0.105 m/sec 2 (A-weighted) and 0.58 m/sec2 (linear). On the basis of present knowledge of the physiologic effects of noise and vibration, we discuss the influence of long-term noise and vibration exposures on the neonate; they provide a threat to carbohydrate, aliphatic compound and protein-enzymatic metabolic transformations and produce changes in cardiovascular, pituitary--adrenal axis and auditory systems.

Humans↗
PubMed1995

Determinants of vibration perception thresholds in IDDM and NIDDM patients.

The relative influence of diabetes mellitus-related and physiological factors on vibration perception thresholds was assessed in 353 patients in a hospital-based setting (173 insulin-dependent and 180 non-insulin dependent patients, aged 51.1 +/- 15.9 years) and 80 healthy controls (aged 43.3 +/- 15.2 years) employing a Biothesiometer. Vibration perception thresholds were bilaterally measured at the thumbs, medial malleoli and halluces. Sixty (17.0%) older patients had off-scale thresholds (> 50 V). As no systematic side differences were found, values of contralateral sites were averaged. Considering the effects of age, height, gender and skin temperature in controls, age accounted for 46.7 and 52.2% threshold variance at the ankles and halluces, respectively, while height explained 5.1 and 5.1%, respectively. At the thumbs, only age was of relevance. Age relationships with vibration thresholds in health did not differ from published reports at any site. In the patient group, influences of age, height, gender, skin temperature, years from diagnosis, HbAlc, serum creatinine, drop in systolic blood pressure on standing, and ankle/arm blood pressure indices were assessed for each type of diabetes. For both types, age and height again had relevant effects at the lower extremities as did age and gender at the thumbs. Skin temperature was only marginally significant at the halluces of NIDDM patients. Of the disease-related factors, HbAlc had the strongest effect: for both IDDM and NIDDM higher levels were associated with lower vibration sensitivity. Increasing disease duration led to significantly higher thresholds in IDDM patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Use of motor nerve conduction testing and vibration sensitivity testing as screening tools for carpal tunnel syndrome in industry.

Increased attention to carpal tunnel syndrome in industry has resulted in the development of several proposed screening tests. This investigation evaluated the use of two portable devices for measuring motor nerve conduction time and tactile sensitivity to 120 Hz vibration in a field setting. Forty-seven control participants, 63 manufacturing plant workers with and without symptoms of carpal tunnel syndrome, and 22 patients with physician-diagnosed carpal tunnel syndrome were tested with the NervePace electroneurometer and the Vibration II vibration threshold measurement device. Nerve conduction time differed significantly between the controls, the asymptomatic workers, and the participants with carpal tunnel syndrome or symptoms of carpal tunnel syndrome. The vibration threshold was higher in the carpal tunnel syndrome group than in the other groups; however, further examination of the data revealed no differences in threshold unless nerve conduction time exceeded the control mean by at least three standard deviations. The false-negative rates associated with the tests limit their usefulness in screening for carpal tunnel syndrome.

Carpal Tunnel Syndrome↗
PubMed1992

Vibration-induced muscle injury. An experimental model and preliminary findings.

The hind paws of rats were subjected to vibration at a frequency of 80 Hz., an acceleration of 32 m./s.2 rms (i.e. ah.w approximately 6.3 m./s.2 rms) for five hours daily during five consecutive days. Morphological, histochemical and immunohistochemical analyses of the soleus, extensor digitorum longus and the plantar muscles in the vibrated limb and the contralateral control limb were performed. No changes were seen in the soleus or extensor digitorum longus muscles but different degrees of degeneration of the muscle fibres were seen in the plantar muscle sections as well as signs of regeneration. No changes were observed in the contralateral unexposed limb. It is concluded that it is not only nervous tissue but also muscle tissue that can be affected by vibration. The changes seem to be confined to muscles close to the vibration exciter.

Animals↗
PubMed1992

Modification of plant growth and development by acceleration and vibration: concerns and opportunities for plant experimentation in orbiting spacecraft.

Growth, development, and orientation of higher plants is altered by physical disturbances such as shaking, touching, or vibration. Plant growth responses to thigmic (contact rubbing) forces are almost always negative, whereas growth responses to periodic seismic (shaking) or vibric (vibrational) disturbances may be positive or negative, depending on intensity and duration of force, and prevailing environmental conditions. Seedlings are most sensitive to mechanical stress when grown in darkness or under the low-light conditions typically available in plant flight hardware. Brief exposure to physical perturbation causes immediate growth inhibition of dark-grown seedlings followed by gradual recovery of growth rate beginning 10-12 minutes later. For mild vibration, growth rate may overshoot that of undisturbed control plants within an hour of a stress episode, whereas for thigmic stress recovery may remain incomplete for 24 hours or longer. Lack of physical stimulation by gravity should make plants even more responsive to random physical perturbation. Threshold growth response of seedlings to vibrational parameters needs to be determined under real spaceflight conditions.

Acceleration↗
PubMedDate not supplied

On modeling the vibrational spectra of 14-s-cis retinal conformers in bacteriorhodopsin.

The vibrational properties of 13-cis, 14-s-trans and 13-cis, 14-s-cis protonated retinal Schiff base model compounds are explored with MNDO calculations. In particular, the effect of isomerization about the C14-C15 single bond on the vibrational properties of the deuterium in-plane rocking vibrations has been examined. Our MNDO calculations, using a variety of lysine models, lysine conformations and Schiff base charge environments, demonstrate that the C14-D and C15-D in-plane rocking vibrations in the 14,15-dideuterio retinal protonated Schiff base are strongly coupled in 13-cis, 14-s-cis molecules producing a splitting of ca. 80 cm-1 between the symmetric and antisymmetric rocking mode combinations but that these modes are only weakly coupled in 14-s-trans molecules. This analysis demonstrates that the 14,15-dideuterio labeling method developed earlier for determining C14-C15 conformation (S.P.A. Fodor, W. T. Pollard, R. Gebhard, E. M. M. van den Berg, J. Lugtenburg and R. A. Mathies, Proc. Natl. Acad. Sci. USA, 85, (1988) 2156-2160) is valid, and hence that the structure of the retinal chromophore in bacteriorhodopsin's L550 intermediate is 13-cis, 14-s-trans. The reasons for the misleading conclusions derived from MNDO calculations performed earlier by Schulten and Tavan are discussed.

Bacteriorhodopsins↗
PubMed1990

Tissue response to mechanical vibrations for "sonoelasticity imaging".

The goal of "sonoelasticity imaging" is to differentiate between normal soft tissues and hard lesions. This is done by measuring and then displaying the ultrasound Doppler spectrum of regions within tissues which are mechanically forced with low frequency (20-1000 Hz) vibrations. The resolution and sensitivity of the technique ultimately rest on the spatial resolution of ultrasound Doppler detection, the low frequency mechanical properties of tissues, and the vibration response of layered, inhomogeneous regions with hard tumor inclusions and complicated boundary conditions set by the presence of skin, bones and other regions. An initial investigation has measured some tissue stiffness parameters, and applied these in a NASTRAN finite element analysis to simulate a prostate tumor in the pelvic cavity. The measurements show a wide separation between the elastic modulus of tumors and soft tissues such as muscle and prostate. NASTRAN analyses show the ability to delineate regions of different elasticity based on the pattern of vibration amplitudes. The ability to change vibration frequency within the 100-300 Hz band seems particularly helpful in simulations and experiments which visualize small stiff inclusions in tissues. Preliminary results support the postulate that sonoelasticity imaging can provide useful information concerning tissue properties that are not otherwise obtainable.

Computer Simulation↗
PubMed1984

Analgesic effect of vibration and cooling on pain induced by intraneural electrical stimulation.

Psychophysical experiments were carried out on 16 human subjects to determine how low intensity mechanical and thermal skin stimuli interfere with the sensation of pain. Moderate or intense pain was induced by low frequency (2 Hz) electrical stimulation within cutaneous fascicles of the median nerve at wrist level, and vibration, pressure, cooling or warming were applied for short periods (usually 20-60 sec) within or outside the skin area to which the pain was projected. Vibration within the area of projected pain reduced the sensation of pain more efficiently than vibration outside that area. Moderate pain was sometimes completely inhibited but intense pain was only moderately reduced. Pressure and cooling produced some pain relief whereas mild warming had an ambiguous effect. Since the painful input derived from stimulation of fibres in the nerve trunk, and not from peripheral nociceptors, the pain suppressing effects of vibration and cooling are not explicable in terms of lowered excitability of the nociceptive nerve endings in the skin. Instead, the results indicate that activity in low threshold mechanoreceptive and cold sensitive units suppresses pain at central (probably segmental) levels.

Adult↗
PubMed1996

In vivo assessment of bone mechanical properties by vibration and ultrasonic wave propagation analysis.

Vibration analysis and ultrasonic wave propagation analysis were evaluated as noninvasive techniques for the in vivo assessment of bone mechanical properties. The relation between the resonant frequencies, obtained by vibration analysis, and geometrical and material properties of long bones is explained using a simple beam model. This simple beam model was validated experimentally in previous work on excised animal bones. In vitro measurements were performed on human and animal excised bones from specific osteopenic cases and control groups. Using specific protocols for in vivo vibration and ultrasound measurements of the tibia, a population of osteoporotic patients and age-matched controls were tested. From these measurements, it was concluded that the bending rigidity, calculated from the resonant frequencies, in osteoporotic tibiae had decreased as compared to the control group. Also the ultrasound velocity in the tibial cortex was lower in the osteoporotic group. The latter indicates a change in the bone tissue material properties. On the other hand, immobilization osteoporosis appeared to lead to a decrease in bending rigidity without an observable change in bone tissue material properties. By the combination of vibration analysis and ultrasound velocity measurements, the whole bone's mechanical characteristics as well as the bone tissue properties can be assessed in vivo. Since both techniques are noninvasive, they can be used in longitudinal studies for the assessment of bone response on physical loading.

Aged↗
PubMed2004

Vascular and nerve damage in workers exposed to vibrating tools. The importance of objective measurements of exposure time.

The aim of the present study was to compare the development of vibration white fingers (VWF) in workers in relation to different ways of exposure estimation, and their relationship to the standard ISO 5349, annex A. Nineteen vibration exposed (grinding machines) male workers completed a questionnaire followed by a structured interview including questions regarding their estimated hand-held vibration exposure. Neurophysiological tests such as fractionated nerve conduction velocity in hands and arms, vibrotactile perception thresholds and temperature thresholds were determined. The subjective estimation of the mean daily exposure-time to vibrating tools was 192 min (range 18-480 min) among the workers. The estimated mean exposure time calculated from the consumption of grinding wheels was 42 min (range 18-60 min), approximately a four-fold overestimation (Wilcoxon's signed ranks test, p<0.001). Thus, objective measurements of the exposure time, related to the standard ISO 5349, which in this case were based on the consumption of grinding wheels, will in most cases give a better basis for adequate risk assessment than self-exposure assessment.

Acceleration↗
PubMed2006

Solid state characterization of olanzapine polymorphs using vibrational spectroscopy.

FT-Raman, infrared and near infrared investigations of two polymorphs of olanzapine are presented, establishing the main features that allow the discrimination of these crystalline forms using vibrational spectroscopic methods. Ab initio calculations on the basis of the density functional theory were used to determine the stable conformations. The calculated vibrational spectra were compared to the experimental ones in order to identify the conformers corresponding to each polymorph and to assign the vibrational bands to the internal vibrations of the olanzapine molecule. Our results support the hydrogen bonding pattern proposed by the reported crystalline structure and provide valuable information on the structural and thermodynamical relationship between the investigated polymorphs.

Antipsychotic Agents↗
PubMed2006

The effects of load and toothpaste on powered toothbrush vibrations.

OBJECTIVES: The primary cleaning action of powered toothbrushes is the motion of the bristles in contact with the tooth surfaces. The aim of this study was to use scanning laser vibrometry to determine the effects of load and toothpaste on the bristle vibration characteristics of four powered toothbrushes (Oral-B Sonic Complete; Oral-B Professional Care 8000 Series; Sonicare Elite and Ultrasonex). METHODS: Toothbrushes were initially scanned, with the laser vibrometer, under unloaded conditions to provide baseline readings. Toothbrushes were then assessed under loaded conditions (1.00 N and 2.00 N), with and without toothpaste, to observe the effect on bristle motion. RESULTS: Application of 1.00 N load significantly reduced the displacement amplitudes of all powered toothbrushes (p<0.003) except for the Sonicare (p>0.497). With toothpaste, 1.00 N load caused a significant decrease in vibration displacement amplitude for all brushes (p<0.0001). The application of 2.00 N, with and without toothpaste, significantly reduced all toothbrushes vibration displacement amplitude (p<0.0001). Under all investigation conditions, the Oral-B 8000 had the largest vibration displacement amplitude of the toothbrushes tested. CONCLUSIONS: Load and toothpaste significantly affected the performance of powered toothbrushes. Understanding why these factors affect certain toothbrush designs more than others may lead to toothbrushes being designed with greater clinical efficacy.

Analysis of Variance↗
PubMed2004

Whole-body vibration and postural stress among operators of construction equipment: a literature review.

INTRODUCTION: Operators of construction equipment perform various duties at work that expose them to a variety of risk factors that may lead to health problems. A few of the health hazards among operators of construction equipment are: (a) whole-body vibration, (b) awkward postural requirements (including static sitting), (c) dust, (d) noise, (e) temperature extremes, and (f) shift work. It has been suggested that operating engineers (OEs) are exposed to two important risk factors for the development of musculoskeletal disorders: whole-body vibration and non-neutral body postures. METHOD: This review evaluates selected papers that have studied exposure to whole-body vibration and awkward posture among operators of mobile equipment. There have been only few studies that have specifically examined exposure of these risk factors among operators of construction equipment. Thus other studies from related industry and equipment were reviewed as applicable. CONCLUSION: In order to better understand whole-body vibration and postural stress among OEs, it is recommended that future studies are needed in evaluating these risk factors among OEs.

Equipment and Supplies↗