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PubMed1994

Foundations of hand-transmitted vibration standards.

Standards for hand-transmitted vibration predict dependent variables (e.g. finger blanching) from measurements of a few independent variables (e.g. vibration magnitude, vibration frequency, exposure duration). This paper illustrates the assumptions in the current International Standard guidelines for the evaluation of hand-transmitted vibration and compares research methods which may provide information to improve the guidance. Subjective assessments of vibration discomfort have influenced the frequency weighting used in current standards, but the data have been modified greatly for this purpose. Subjective and biodynamic data suggest that the severity of vibration may not be similar for vibration occurring in different axes. Physiological and pathological studies seek to uncover the mechanisms involved in the temporary and permanent changes caused by vibration, but they have yet to contribute to the guidance in standards. Future experimental studies in humans are unlikely to be sufficient to determine how injury depends on the characteristics of vibration exposures at work. Epidemiological studies are required to uncover the effects of occupational exposures, but the complexity of occupational exposures will prevent the formulation of standards based solely on the results of epidemiological studies. Standards for hand-transmitted vibration include unproven assumptions but, for those assessing the severity of occupational exposures, they offer the most reasonable method for predicting the likely effects of vibration. A combination of subjective, biodynamic, physiological, pathological and epidemiological studies is required to improve current guidance.

Hand↗
PubMed1995

Vibration syndrome in railway track maintenance workers.

An inquiry was sent to all railway maintenance workers in three railway districts in Finland and hand-arm vibration was measured on the handlebars of tools used by maintenance workers. The study group included 252 (82%) subjects, whose mean age was 41 years and who had worked in track maintenance for 14 years (SD 9). In Finland there are over 600 railway maintenance workers who use vibrating tools. The frequency-weighted acceleration of hand-arm vibration was calculated according to the ISO 5349 standard. Hand-held tamping machines had caused most of the vibration exposure, and aw4h was 10.6 m/s2 measured on the handlebar of tamping machine, but many workers also used other vibrating tools. The annual vibration level was 2.5 m/s2 when the use of all vibrating tools and the exposure time was taken into account. In the questionnaire the prevalence of vibration-induced white finger (VWF) was 14% in the entire material, and the prevalence of VWF increased significantly with the total duration of the maintenance work. In addition, 39% of the subjects had suffered numbness of the hands, and the prevalence of hand numbness also increased significantly with the total duration of maintenance work. According to the measurements of vibration and the prevalence of hand symptoms the present investigation indicates vibration syndrome as being related to railway track maintenance work. In the exposure group, where tamping machines mainly were used and exposure to other vibration was small, the prevalence of VWF was also significantly higher, but the prevalence of hand numbness insignificant compared with the control group. In this study vascular and nerve hand symptoms were considered to cause serious trouble in work by 4-11% of the maintenance workers.

Adult↗
PubMed1994

Nanometer scale vibration in mutant axonemes of Chlamydomonas.

Flagellar axonemes of sea urchin sperm display high frequency (200-400 Hz) vibration with nanometer scale amplitudes in the presence of ATP [Kamimura and Kamiya, 1992: J. Cell Biol. 116:1443-1454]. To investigate how various axonemal components affect the vibration, we examined vibration in wild-type and mutant axonemes of Chlamydomonas. At 1 mM ATP, wild-type axonemes underwent vibration at 100-650 Hz with amplitudes of 4-40 nm. This vibration was similar to, but less regular than, that in sea urchin sperm. Axonemes of the mutants ida1 and ida4 lacking part of the inner arm dynein underwent vibrations indistinguishable from that of wild-type. The mutant oda1 lacking the entire outer arm underwent vibration at about half the wild-type frequency. Unexpectedly, the paralyzed mutants pf18 lacking the central pair and pf14 lacking the radial spokes displayed vibration with significantly higher frequencies and smaller amplitudes than those in the wild-type vibration. These results indicate that the high-frequency vibration is common to many kinds of mutant axonemes that lack various axonemal substructures, but that its manner is sensitive to the presence of outer arm dynein and the central pair/radial spoke system. Simultaneous measurements of amplitude and frequency in wild-type and mutant axonemes suggest that the velocity of microtubule sliding in vibrating axonemes is lower than the velocity of sliding under load-free conditions. The velocity is particularly low in pf18.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2004

Mode-specific photoelectron scattering effects on CO2(+)(C2Sigmag+) vibrations.

Using high-resolution photoelectron spectroscopy, we have determined the energy dependent vibrational branching ratios for the symmetric stretch [v+ = (100)], bend [v+ = (010)], and antisymmetric stretch [v+ = (001)], as well as several overtones and combination bands in the 4sigmag(-1) photoionization of CO2. Data were acquired over the range from 20-110 eV, and this wide spectral coverage highlighted that alternative vibrational modes exhibit contrasting behavior, even over a range usually considered to be dominated by atomic effects. Alternative vibrational modes exhibit qualitatively distinct energy dependences, and this contrasting mode-specific behavior underscores the point that vibrationally resolved measurements reflect the sensitivity of the electron scattering dynamics to well-defined changes in molecular geometry. In particular, such energy-dependent studies help to elucidate the mechanism(s) responsible for populating the symmetry forbidden vibrational levels [i.e., v+ =( 010), (001), (030), and (110)]. This is the first study in which vibrationally resolved data have been acquired as a function of energy for all of the vibrational modes of a polyatomic system. Theoretical Schwinger variational calculations are used to interpret the experimental data, and they indicate that a 4sigmag-->ksigmau shape resonance is responsible for most of the excursions observed for the vibrational branching ratios. Generally, the energy dependent trends are reproduced well by theory, but a notable exception is the symmetric stretch vibrational branching ratio. The calculated results display a strong peak in the vibrational branching ratio while the experimental data show a pronounced minimum. This suggests an interference mechanism that is not accounted for in the single-channel adiabatic-nuclei calculations. Electronic branching ratios were also measured and compared to the vibrational branching ratios to assess the relative contributions of interchannel (i.e., Herzberg-Teller) versus intrachannel (i.e., photoelectron-mediated) coupling.

Carbon Dioxide↗
PubMed2002

Vibration-induced shift of the subjective visual horizontal: a sign of unilateral vestibular deficit.

BACKGROUND: Vibration to the head or neck excites vestibular and neck muscle spindle afferents. Can such vibrations improve the sensitivity of the subjective visual horizontal (SVH) test to chronic unilateral deficit of the vestibular system? DESIGN: Controlled experimental study. SETTING: Tertiary referral center. PATIENTS AND CONTROLS: Thirteen healthy subjects and 23 patients with chronic unilateral vestibular deficits after vestibular neurectomy or neurolabyrinthitis. Results of head-impulse test showed unilateral loss of function of all 3 semicircular canals in 14 patients and loss of anterior and lateral semicircular canals in 9 patients. INTERVENTION: Unilateral vibration (92 Hz; 0.6-mm amplitude) applied to sternocleidomastoid muscle (SCM) or mastoid bone. MAIN OUTCOME MEASURE: Results of SVH test (in degrees). RESULTS: Without vibration, 13 of 23 patients and all healthy subjects had SVH of less than 3 degrees (sensitivity, 43%; specificity, 100%). During vibration to the ipsilesional SCM, SVH increased to greater than 3 degrees in 21 of 23 patients but in only 1 of 13 healthy subjects (sensitivity, 91%; specificity, 92%). The patient group had significantly greater SVH shifts to the ipsilesional side than did healthy subjects in response to SCM and mastoid bone vibration on either side. The SVH shift during vibration to the ipsilesional SCM was significantly greater than that during vibration to the contralesional muscle (P<.001) or to the mastoid bone on either side (P<.05). The vibration-induced SVH shift was significantly greater in those patients with loss of 3 semicircular canals than in those with loss of 2 (P<.01). CONCLUSIONS: The sensitivity of the SVH test to chronic unilateral vestibular deficits can be improved by applying vibration to the SCM. The magnitude of vibratory SVH shift is related to the extent of unilateral deficit of the otolithic organs, vertical canals, or both.

Adult↗
PubMed1991

Responses of primary endings of cat muscle spindles to locally applied vibration.

Responses of muscle spindles in the cat soleus muscle have been studied during vibration applied locally to the belly of the muscle. Bursts of vibration at 170 Hz and with a peak amplitude of 200 microns were applied to a site at which local pressure initiated impulses from the spindle. The response to vibration depended on the conditioning of the muscle immediately beforehand and the placement of the vibrator. The length at which the vibration was applied was called the test length; this was typically 10 mm less than the muscle's maximum length in the body. After a fusimotor strength contraction at a length 2-5 mm longer than the test length, vibration sensitivity, measured on return to the test length, was low. If the muscle was contracted at a length 2-5 mm shorter than the test length, vibration sensitivity was high. The low vibration sensitivity following conditioning at the longer length was attributed to the development of slack in intrafusal fibres. In the presence of slack, stimulation of some static fusimotor fibres was able to restore vibration sensitivity fully. It is suggested that the vibration sensitivity of passive spindles arises largely in bag2 intrafusal fibres.

Animals↗
PubMed1996

Uterine circulatory dysfunction induced by whole-body vibration and its endocrine pathogenesis in the pregnant rat.

Effects of whole-body vibration on normal pregnancy were studied in the rat. Uterine blood flow and five endocrine functions corticosterone (CS), estradiol (E2), progesterone (P), prostaglandin E2 (PGE2) and prostaglandin F2 alpha (PGF2 alpha) concentration were measured in rats exposed to whole-body vibration with an acceleration of 10 m.s-2 at a frequency of 8 Hz. While no change in uterine blood flow was observed in control rats, uterine blood flow was significantly decreased 75 and 90 min after exposure to vibration. The uterine blood flow at 15 and 30 min was increased by pretreatment with intraperitoneal injections of angiotensin II (AII). In contrast, in AII pretreated rats exposed to the vibration, uterine blood flow was significantly reduced 90 min after exposure. The CS concentration was increased by vibration independently of the pretreatment with AII. Neither E2 nor PGF2 alpha concentration were changed by the vibration with or without AII administration. The P and PGE2 concentrations were both decreased by vibration in the absence of AII, while the decrease in PGE2 induced by the vibration was also found in AII-treated rats. The present results indicated that the pregnant rats subjected to whole-body vibration responded with changes in uterine and ovarian function. The observed decrease in uterine blood flow may have been the result of reduced PGE2 concentration resulting from an indirect effect of vibration.

Animals↗
PubMed2004

Effects of whole-body vibration exercise on the endocrine system of healthy men.

Whole-body vibration is reported to increase muscle performance, bone mineral density and stimulate the secretion of lipolytic and protein anabolic hormones, such as GH and testosterone, that might be used for the treatment of obesity. To date, as no controlled trial has examined the effects of vibration exercise on the human endocrine system, we performed a randomized controlled study, to establish whether the circulating concentrations of glucose and hormones (insulin, glucagon, cortisol, epinephrine, norepinephrine, GH, IGF-1, free and total testosterone) are affected by vibration in 10 healthy men [age 39 +/- 3, body mass index (BMI) of 23.5 +/- 0.5 kg/m2, mean +/- SEM]. Volunteers were studied on two occasions before and after standing for 25 min on a ground plate in the absence (control) or in the presence (vibration) of 30 Hz whole body vibration. Vibration slightly reduced plasma glucose (30 min: vibration 4.59 +/- 0.21, control 4.74 +/- 0.22 mM, p=0.049) and increased plasma norepinephrine concentrations (60 min: vibration 1.29 +/- 0.18, control 1.01 +/- 0.07 nM, p=0.038), but did not change the circulating concentrations of other hormones. These results demonstrate that vibration exercise transiently reduces plasma glucose, possibly by increasing glucose utilization by contracting muscles. Since hormonal responses, with the exception of norepinephrine, are not affected by acute vibration exposure, this type of exercise is not expected to reduce fat mass in obese subjects.

Adult↗
PubMed2002

Effects of tendon vibration on the spatiotemporal characteristics of human locomotion.

The present study addressed the involvement of proprioceptive input of the muscle spindles in the spatiotemporal control of human locomotion. Blindfolded subjects walked along a walkway while tendon vibration, a powerful stimulus of Ia afferents, was applied to various muscles of the lower limb. The effects of tendon vibration were measured on joint kinematics and on intralimb and interlimb coordination. Tendon vibration of the tibialis anterior during locomotion led to a decreased plantar flexion at toe-off, whereas vibration of the triceps surae led to a decreased dorsiflexion during swing. Vibration of the quadriceps femoris at the knee led to a decreased knee flexion during swing. These local effects of vibration can be explained in the light of a lengthening illusion of the vibrated muscle in that phase of the gait cycle where the muscle is lengthened. Tendon vibration did not affect the qualitative features of intralimb coordination. With respect to interlimb coordination, only vibration of the biceps femoris showed a significant increase in phase lead of the vibrated limb. The present results suggest the involvement of Ia afferent input in the online control of joint rotations. Additionally it is hypothesized that the proprioceptive input of biceps femoris might be involved in the control of coordination between the limbs, whereas the coordination between the segments of one limb appears to be unaffected by disturbance of muscle spindle input of one muscle.

Adult↗
PubMed1997

Combined effects of hand-arm vibration and noise on temporary threshold shifts of hearing in healthy subjects.

OBJECT: To investigate whether hand-arm vibration and noise have a combined effect on temporary threshold shift (TTS) of hearing among healthy subjects. METHOD AND DESIGN: Nineteen healthy subjects with an average age of 25.7 (SD 7.7) years were exposed to vibration (30 m/s2, 60 Hz), noise [90 dB(A)] and both, respectively. The subject's right hand was placed on the plate of a vibrator and the right ear exposed to noise via headphones. Subjects were exposed to vibration and/or noise for 3 min and after a 1-min pause the exposure was repeated five times. Hearing thresholds at 1, 4 and 6 kHz were measured during the time periods before, between (during pauses) and after exposure. RESULTS: Exposure to vibration alone caused almost no hearing threshold changes at every frequency tested. But exposure to noise or a combination of vibration and noise caused a significant increase in TTSs at 4 and 6 kHz. Moreover, exposure to a combination of vibration and noise caused significantly higher TTSs than exposure to noise at 4 and 6 kHz. CONCLUSION: The present results demonstrate the combined effects of hand-arm vibration and noise can enhance exposure to hand-arm vibration and noise can enhance the TTS of hearing more than noise exposure, though hand-arm vibration alone may hardly affect TTS.

Adult↗
PubMed1998

Exposure-response relationship in the hand-arm vibration syndrome: an overview of current epidemiology research.

The complex of vascular, neurologic, and osteoarticular disorders occurring in the upper limbs of vibration-exposed workers is called hand-arm vibration syndrome. There is epidemiologic evidence for an increased occurrence of peripheral sensorineural disorders in occupational groups working with vibrating tools. An excess risk for wrist osteoarthrosis and for elbow arthrosis and osteophytosis has been reported in workers exposed to shocks and low-frequency vibration of high magnitude from percussive tools. However, there are too few epidemiology data to enable reliable conclusions to be drawn about exposure-response relationships for both sensorineural disturbances and bone and joint disorders caused by hand-transmitted vibration. Cross-sectional and longitudinal epidemiology studies have shown that occupational exposure to hand-transmitted vibration from a great variety of hand-held tools is significantly associated with an increased occurrence of digital vasospastic disorders called vibration-induced white finger (VWF). The proposal of an exposure-response relationship for VWF has been included in an annex to the international standard ISO 5349. The findings of several epidemiology studies have shown a poor agreement between the risk for VWF observed in various occupational groups and that predicted by the ISO 5349 model. Both overestimation and underestimation of the occurrence of VWF have been reported by investigators. It has been argued that the current ISO frequency-weighting curve for hand-transmitted vibration may be inappropriate for the assessment of vibration-induced adverse vascular effects. Alternative exposure-response relationships for VWF have been suggested in recent epidemiology studies. The epidemiology data used to construct current exposure-response relationships for vibration-induced injuries are primarily derived from cross-sectional studies. Future epidemiology research should be based on prospective cohort studies because the design characteristics of such studies permit the study of cause-effect relationships and the formulation of etiologic hypotheses.

Adult↗
PubMed1986

Effects of tendon vibration on unimanual and bimanual movement accuracy.

Vibration-induced changes in target accuracy were examined to determine the influence of afferent information on unimanual and bimanual movements. Normal adult male subjects (N = 4) undertook a 90 degrees curvilinear positioning task (flexion and extension of the elbow) in the absence of vision. Each trial required the subject to reproduce a criterion target position while one of three vibration treatments was applied to the distal aspect of the triceps brachii tendon of the dominant arm. Vibration (100 Hz) was administered manually either prior to or concurrently with movement. Subsequent movement outcome was compared with a control or no-vibration condition. In the unimanual condition application of vibration to an antagonist muscle produced consistent undershoot of approximately 10 to 12% of the total movement amplitude. In contrast, vibration of the agonist produced minimal error in movement. A similar pattern was seen in the vibrated dominant arm of the bimanual condition; however, the results exhibited no interaction between hands. Target accuracy during prior vibration did not differ significantly from control trials and we concluded that vibration was an inappropriate stimulus to distort initial condition information. The observed results are consistent with vibration-induced activation of muscle spindle receptors in the lengthening muscle during movement. We concluded that afferent information from an antagonist muscle is critically important in the final movement outcome, but there was no evidence of contralateral effects.

Adult↗
PubMed1984

Measurement of whole-body vibration by double-pulsed holography.

A technique for registering vibration and deformation patterns has been adapted for the measurement of whole-body vibration in humans. Double-exposure holographic interferometry produces three dimensional pictures of the body, allowing exact measurement of the subject's movement between the two pulses. In this study an interval of 600 microseconds between the two pulses was used, producing measurements with a resolution of less than 0.3 X 10(-6)m. The subject standing in a fixed posture, was exposed to the laser beams first without vibration and then with vibration. The picture without vibration is needed as certain movements due to life functions of the body such as heartbeat, blood circulation etc are involved therein. This basic pattern should be considered when analysing the pictures with vibration. Different types of vibration in various postures were studied. Tests were also conducted when a reflective coating was applied to the skin. The results show that the method is applicable for measuring whole-body vibration and suggests further tests with more modern laser equipment which is now available. Such equipment can produce pulses with a high repetition rate and of much better quality than those obtained in this study. Once coordinated to the heartbeat and to the working frequency of the vibrating object, a reliable analysis of whole-body vibration can be maintained.

Holography↗
PubMed1984

Cyclobenzaprine: effect on tonic vibration reflexes in local tetanus cat preparations.

Local tetanus was induced by the injection of toxin into the gastrocnemius-soleus muscle of cats. After 48 hr, longitudinal vibration of the muscle was used to elicit a reflex contraction (tonic vibration reflex, TVR). In other experiments, electrical stimulation of various regions of the central nervous system served to elicit contraction of the muscle alone or to facilitate a vibration (150 mu at 300 Hz)-induced tonic vibration reflex. In contrast with normal animals, tonic vibration reflex responses in local tetanus preparations of decerebrate cats were augmented after transection of the spinal cord at Cl. In decerebrate local tetanus preparations, a dose-related reduction of tonic vibration reflex responses, induced at all frequencies and amplitudes of muscle vibration, was observed after doses of 0.5 to 3.5 mg/kg (i.v.) of cyclobenzaprine. Muscle contractions induced by stimulation of the medial reticular formation and facilitation of tonic vibration reflex responses were more sensitive to the action of cyclobenzaprine than were similar responses activated through stimulation of Deiters' lateral vestibular nucleus. In spinal preparations, tonic vibration reflex responses were only moderately reduced after similar doses of cyclobenzaprine. Contractions induced by stimulation of the spinal cord (T6) and facilitated tonic vibration reflex responses were only moderately reduced, whereas the post-stimulus-induced facilitations were considerably attenuated. Thus, experiments in local tetanus preparations support further the concept that the major site of action of cyclobenzaprine is supraspinal, whereas its action upon spinal structures contributes to its overall skeletal muscle-relaxant activity.

Amitriptyline↗
PubMed1998

Effect of frequency and amplitude of vibration on void formation in dies poured from polyvinyl siloxane impressions.

STATEMENT OF PROBLEM: Numerous factors are involved in making a void-free dental stone cast from a polyvinyl siloxane impression. PURPOSE: The aim of this study was to determine whether frequency and amplitude of vibration had any effect on the formation of voids on the cast surface poured from polyvinyl siloxane impression with a mechanical model vibrator. MATERIAL AND METHODS: Impressions were poured in dental stone with a mechanical model vibrator that was set at vibration frequency 3000 cycles/min (low) and 6000 cycles/min (high) by a knob. The amplitude of vibration is provided in 5 steps and remained constant for the step set on the instrument. A total of 240 casts were prepared. The vibrator was set at low frequency and 30 impressions were poured for each of the 5 steps of amplitude. The vibrator was then set at high frequency and 30 impressions were poured for each of the 5 steps of amplitude. The resultant casts were examined for the presence of surface voids under 10 x magnification. RESULTS: Means for voids in all cast groups calculated for low and high vibration frequencies indicated that an increase in the amplitude of vibration caused an increase in the number of voids on the die surface. CONCLUSION: Use of high frequency of vibration 6000 cycles/min and 0.40 mm amplitude produced significantly fewer voids (P < .0001) compared with steps 4 (0.45 mm) and 5 (0.80 mm) amplitude.

Analysis of Variance↗
PubMed1996

Impaired regeneration in rat sciatic nerves exposed to short-term vibration.

We have studied the effects of vibration on the regeneration capacity of the peripheral nerve. A rat model was used where one hind limb was subjected to vibration of defined magnitude and duration while the contralateral hind limb was not exposed to vibration. Seven days later, the sciatic nerves were transected bilaterally and cross-joined giving the following groups: group A, a proximal vibrated nerve end sutured to a non-vibrated distal nerve end; group B, a non-vibrated proximal nerve end sutured to a distal vibrated nerve end, and group C, non-vibrated proximal nerve end sutured to a non-vibrated distal nerve end. The regeneration distances were measured 3, 6 and 8 days after surgery. The control group showed a normal linear outgrowth. The outgrowth in the two experimental groups was initially not different to controls but later became significantly different, indicating a retardation of outgrowth in these groups. It is concluded that short-term exposure to vibration can impair nerve regeneration after transection and nerve repair.

Animals↗
PubMed2001

Examination of the myoelectric activity of back muscles during random vibration--methodical approach and first results.

OBJECTIVE: To elaborate methods for an elimination of artefacts and the analysis of the relationship between random whole-body vibration and electromyographic responses of back muscles. DESIGN: A procedure involving wavelets and digital filtering has been used for the removal of artefacts from the electromyogram during whole-body vibration. BACKGROUND: Back muscle forces contribute essentially to the whole-body vibration-induced spinal load. The electromyogram can help to estimate these forces during whole-body vibration. METHODS: 38 subjects were exposed to identical random low-frequency whole-body vibration. Artefacts caused by the electrocardiogram in the electromyogram were identified by appropriate wavelets and eliminated in the time-domain. After averaging the individual high-pass filtered and rectified undistorted electromyograms across subjects, the transfer function from seat acceleration to the average electromyogram was determined and used for the prediction of the electromyogram. RESULTS: A sufficient procedure involving wavelets and digital filtering has been elaborated for the removal of artefacts from the electromyogram of back muscles during whole-body vibration. A systematic relationship between random vibration and back muscle-response was obtained and described. The transfer function suggests two different reflex-mechanisms - one elicited below, the other above 4 Hz. CONCLUSIONS: The approach of analysing and predicting the muscle-response to random vibration by using the transfer function seems to be promising and could be a valuable tool for the future calculation of muscle forces as an input to active models. RELEVANCE: The knowledge of the extent and timing of the back muscle-response to random whole-body vibration is relevant for an improved evaluation of whole-body vibration with respect to health.

Adult↗
PubMedDate not supplied

Mechanical vibration in neonatal transport: a randomized study of different mattresses.

OBJECTIVE: To test the hypothesis that a gel mattress is most effective in attenuating mechanical vibration in neonatal transport, we performed a randomized block study of four mattress combinations (none, foam, gel, gel on foam) using mannequins and an ambulance traveling on fixed routes (city, highway). STUDY DESIGN: Mechanical vibration was assessed by measuring vertical accelerations at two locations: the forehead of a 2000-gm mannequin and the transport incubator base. From time histories of these accelerations, root mean square (RMS) values and power spectral density functions were calculated. The effect of the mattress on the transmission of vibration was determined from ratios of the RMS values at the two locations. An RMS ratio of < 1.0 indicates attenuation, whereas a ratio of > 1.0 indicates accentuation of vibration. From the power spectral density functions, the natural frequency of the system was determined for each mattress combination in relation to the natural frequencies of the ambulance. To determine the effect of the weight of the mannequin on vibration, additional measurements were performed using a 300-gm mannequin. RESULTS: All the observed RMS ratios were > 1. The highest ratios were observed on the city route in the absence of the gel mattress. The gel mattress, used alone or with the foam mattress, in contrast to foam or no mattress, shifted the natural frequency of the system away from the natural frequencies of the ambulance, avoiding a large amplification of vibration. A decrease in the weight of the mannequin caused the gel mattress to be less effective in attenuating vibration. CONCLUSION: A gel mattress, used alone or with a foam mattress, results in the least accentuation of vibration, but vibration in ambulance transport is not attenuated by any of the mattress combinations. The hazard of vibration may be particularly relevant when transporting extremely low birth weight neonates. These findings indicate a need for study and design of more effective devices that can reduce the vibratory stress.

Acceleration↗