Quantifying supine human discomfort in off-road whole-body vibration.

This work presents a new methodology to quantify supine human discomfort during transport when multi-axis whole-body vibration (WBV) and shocks are present. The methodology employs a new scheme to normalise the reported discomfort. Twenty-six human subjects were tested under different off-road conditions and their reported discomforts collected. The paired Wilcoxon signed-rank method was used to investigate the significant differences (p < 0.01) between different track sections on the normalised reported discomfort from the subjects. Analyses based on ISO 2631-1 showed weak correlation with the reported discomfort when significant lateral motions existed. The results with the new formulation showed that discomfort is highly correlated with the vibration dose value at the head of the supine human during WBV (p < 0.001). These results are consistent with previous published work showing that discomfort based on motion at the head-neck region comprises more than 70% of the reported discomfort during supine transport under multiple-axis WBV.Practitioner summary: There are shortcomings in the current approaches to quantifying discomfort of supine humans in multi-axis whole-body vibration where lateral motions are excessive. This study revealed that reported discomfort is strongly related to the vibration dose value at the head of supine subjects rather than the input motion to the body.Abbreviations: WBV: whole-body vibration; RMS: root-mean square; VDV: vibration dose value; PSD: power spectral density; RDn: reported discomfort; NDn: normalized discomfort; : discomfort scaling coefficient; aw(t): frequency-weighted acceleration; wRMS: weighted root-mean square; Aw: weighted root-mean square acceleration; Aw,p: point weighted root-mean square acceleration; Wd: frequency-weighting factor; Wk: frequency-weighting factor; kx: weighed acceleration multiplying factor in x-direction; ky: weighed acceleration multiplying factor in y-direction; kz: weighed acceleration multiplying factor in z-direction; CV: coefficient of variation; VDVp: point vibration dose value; SD: standard deviation; pVTV: point vibration total value.

Low-Frequency Vibrations Enhance Thrombolytic Therapy and Improve Stroke Outcomes.

Background and Purpose- We aim to determine the potential impact on stroke thrombolysis of drip-and-ship helicopter flights and specifically of their low-frequency vibrations (LFVs). Methods- Mice with a middle cerebral artery autologous thromboembolic occlusion were randomized to receive rtPA (recombinant tissue-type plasminogen activator; or saline) 90 minutes later in 3 different settings: (1) a motion platform simulator that reproduced the LFV signature of the helicopter, (2) a standardized actual helicopter flight, and (3) a ground control. Results- Mice assigned to the LFV simulation while receiving tPA had smaller infarctions (31.6 versus 54.9 mm3; P=0.007) and increased favorable neurological outcomes (86% versus 28%; P=0.0001) when compared with ground controls. Surprisingly, mice receiving tPA in the helicopter did not exhibit smaller infarctions (47.8 versus 54.9 mm3; P=0.58) nor improved neurological outcomes (37% versus 28%; P=0.71). This could be due to a causative effect of the 20- to 30-Hz band, which was inadvertently attenuated during actual flights. Mice using saline showed no differences between the LFV simulator and controls with respect to infarct size (80.9 versus 95.3; P=0.81) or neurological outcomes (25% versus 11%; P=0.24), ruling out an effect of LFV alone. There were no differences in blood-brain barrier permeability between LFV simulator or helicopter, compared with controls (2.45-3.02 versus 4.82 mm3; P=0.14). Conclusions- Vibration in the low-frequency range (0.5-120 Hz) is synergistic with rtPA, significantly improving the effectiveness of thrombolysis without impairing blood-brain barrier permeability. Our findings reveal LFV as a novel, safe, and simple-to-deliver intervention that could improve the outcomes of patients. Visual Overview- An online visual overview is available for this article.

Comparing the Efficacy of Methods for Immobilizing the Cervical Spine.

STUDY DESIGN: This was a prospective simulator study with 16 healthy male subjects. OBJECTIVE: The aim of this study was to compare the relative efficacy of immobilization systems in limiting involuntary movements of the cervical spine using a dynamic simulation model. SUMMARY OF BACKGROUND DATA: Relatively few studies have tested the efficacy of immobilization methods for limiting involuntary cervical movement, and only one of these studies used a dynamic simulation system to do so. METHODS: Immobilization configurations tested were cot alone, cot with cervical collar, long spine board (LSB) with cervical collar and head blocks, and vacuum mattress (VM) with cervical collar. A motion platform reproduced shocks and vibrations from ambulance and helicopter field rides, as well as more severe shocks and vibrations that might be encountered on rougher terrain and in inclement weather (designated as an "augmented" ride). Motion capture technology quantitated involuntary cervical rotation, flexion/extension, and lateral bend. The mean and 95% confidence interval of the mean were calculated for the root mean square of angular changes from the starting position and for the maximum range of motion. RESULTS: All configurations tested decreased cervical rotation and flexion/extension relative to the cot alone. However, the LSB and VM were significantly more effective in decreasing cervical rotation than the cervical collar, and the LSB decreased rotation more than the VM in augmented rides. The LSB and VM, but not the cervical collar, significantly limited cervical lateral bend relative to the cot alone. CONCLUSION: Under the study conditions, the LSB and the VM were more effective in limiting cervical movement than the cervical collar. Under some conditions, the LSB decreased repetitive and acute movements more than the VM. Further studies using simulation and other approaches will be essential for determining the safest, most effective configuration should providers choose to immobilize patients with suspected spinal injuries. LEVEL OF EVIDENCE: 3.

Comparing the Efficacy of Methods for Immobilizing the Thoracic-Lumbar Spine.

OBJECTIVE: The purpose of this study was to compare the relative efficacy of immobilization systems in limiting thoracic-lumbar movements. METHODS: A dynamic simulation system was used to reproduce transport-related shocks and vibration, and involuntary movements of the thoracic-lumbar region were measured using 3 immobilization configurations. RESULTS: The vacuum mattress and the long spine board were generally more effective than the cot alone in reducing thoracic-lumbar rotation and flexion/extension. However, the vacuum mattress reduced these thoracic-lumbar movements to a greater extent than the long spine board. In addition, the vacuum mattress significantly decreased thoracic-lumbar lateral movement relative to the cot alone under all simulated transport conditions. In contrast, the long spine board allowed greater lateral movement than the cot alone in a number of the simulated transport rides. CONCLUSION: Under the study conditions, the vacuum mattress was more effective for limiting involuntary movements of the thoracic-lumbar region than the long spine board. Moreover, the increased lateral bend observed with the long spine board under some conditions suggests it may be inadequate for immobilizing this anatomic region as presently designed. Should emergency medical service providers choose to immobilize patients with suspected injuries of the thoracic-lumbar spine, study results support the use of the vacuum mattress.

Predictive discomfort of supine humans in whole-body vibration and shock environments.

This work presents a predictive model to evaluate discomfort associated with supine humans during transportation, where whole-body vibration and repeated shock are predominant. The proposed model consists of two parts: (i) static discomfort resulting from body posture, joint limits and ambient discomfort; and (ii) dynamic discomfort resulting from the relative motion between the body segments as a result of transmitted vibration. Twelve supine subjects were exposed to single and 3D random vibrations and 3D shocks mixed with vibrations. The subjects' reported discomfort and biodynamic response were analysed under different support conditions, including a rigid surface, a stretcher and a stretcher with a spinal backboard. The results demonstrated good correlations between the predictive discomfort and the reported discomfort for the different conditions under consideration, with R(2) = 0.69-0.94 for individual subjects and R(2) = 0.94 for the group mean. The results also indicated a strong relationship between the head-neck and trunk angular velocities and discomfort during supine transportation. Practitioner Summary: The quantification of discomfort of supine humans under vibration and shocks by using a predictive model is an important contribution to this field, whereby the efficacy of different transport systems can be compared. The predictive discomfort model can be used as design criteria for ergonomic enhancement in supine transportation of humans.

Predictive discomfort in single- and combined-axis whole-body vibration considering different seated postures.

OBJECTIVE: The aim of this study was to develop a predictive discomfort model in single-axis, 3-D, and 6-D combined-axis whole-body vibrations of seated occupants considering different postures. BACKGROUND: Non-neutral postures in seated whole-body vibration play a significant role in the resulting level of perceived discomfort and potential long-term injury. The current international standards address contact points but not postures. METHOD: The proposed model computes discomfort on the basis of static deviation of human joints from their neutral positions and how fast humans rotate their joints under vibration. Four seated postures were investigated. For practical implications, the coefficients of the predictive discomfort model were changed into the Borg scale with psychophysical data from 12 volunteers in different vibration conditions (single-axis random fore-aft, lateral, and vertical and two magnitudes of 3-D). The model was tested under two magnitudes of 6-D vibration. RESULTS: Significant correlations (R = .93) were found between the predictive discomfort model and the reported discomfort with different postures and vibrations. The ISO 2631-1 correlated very well with discomfort (R2 = .89) but was not able to predict the effect of posture. CONCLUSION: Human discomfort in seated whole-body vibration with different non-neutral postures can be closely predicted by a combination of static posture and the angular velocities of the joint. APPLICATION: The predictive discomfort model can assist ergonomists and human factors researchers design safer environments for seated operators under vibration. The model can be integrated with advanced computer biomechanical models to investigate the complex interaction between posture and vibration.

Predictive discomfort of non-neutral head-neck postures in fore-aft whole-body vibration.

It seems obvious that human head-neck posture in whole-body vibration (WBV) contributes to discomfort and injury risk. While current mechanical measures such as transmissibility have shown good correlation with the subjective-reported discomfort, they showed difficulties in predicting discomfort for non-neutral postures. A new biomechanically based methodology is introduced in this work to predict discomfort due to non-neutral head-neck postures. Altogether, 10 seated subjects with four head-neck postures--neutral, head-up, head-down and head-to-side--were subjected to WBV in the fore-aft direction using discrete sinusoidal frequencies of 2, 3, 4, 5, 6, 7 and 8 Hz and their subjective responses were recorded using the Borg CR-10 scale. All vibrations were run at constant acceleration of 0.8 m/s² and 1.15 m/s². The results have shown that the subjective-reported discomfort increases with head-down and decreases with head-up and head-to-side postures. The proposed predictive discomfort has closely followed the reported discomfort measures for all postures and rides under investigation. STATEMENT OF RELEVANCE: Many occupational studies have shown strong relevance between non-neutral postures, discomfort and injury risk in WBV. With advances in computer human modelling, the proposed predictive discomfort may provide efficient ways for developing reliable biodynamic models. It may also be used to assess discomfort and modify designs inside moving vehicles.