Vibration causes acute vascular injury in a two-step process: vasoconstriction and vacuole disruption

Sound and Vibration as Research Variables in Terrestrial Vertebrate Models

Sound and vibration have been shown to alter animal behavior and induce physiological changes as well as to cause effects at the cellular and molecular level. For these reasons, both environmental factors have a considerable potential to alter research outcomes when the outcome of the study is dependent on the animal existing in a normal or predictable biological state. Determining the specific levels of sound or vibration that will alter research is complex, as species will respond to different frequencies and have varying frequencies where they are most sensitive. In consideration of the potential of these factors to alter research, a thorough review of the literature and the conditions that likely exist in the research facility should occur specific to each research study. This review will summarize the fundamental physical properties of sound and vibration in relation to deriving maximal level standards, consider the sources of exposure, review the effects on animals, and discuss means by which the adverse effects of these factors can be mitigated.

Riveting hammer vibration damages mechanosensory nerve endings

Hand-arm vibration syndrome (HAVS) is an irreversible neurodegenerative, vasospastic, and musculoskeletal occupational disease of workers who use powered hand tools. The etiology is poorly understood. Neurological symptoms include numbness, tingling, and pain. This study examines impact hammer vibration-induced injury and recoverability of hair mechanosensory innervation. Rat tails were vibrated 12 min/d for 5 weeks followed by 5 week recovery with synchronous non-vibrated controls. Nerve fibers were PGP9.5 immunostained. Lanceolate complex innervation was compared quantitatively in vibrated vs sham. Vibration peak acceleration magnitudes were characterized by frequency power spectral analysis. Average magnitude (2515 m/s² , root mean squared) in kHz frequencies was 109 times that (23 m/s² ) in low Hz. Percentage of hairs innervated by lanceolate complexes was 69.1% in 5-week sham and 53.4% in 5-week vibration generating a denervation difference of 15.7% higher in vibration. Hair innervation was 76.9% in 5-weeks recovery sham and 62.0% in 5-week recovery vibration producing a denervation difference 14.9% higher in recovery vibration. Lanceolate number per complex (18.4 ± 0.2) after vibration remained near sham (19.3 ± 0.3), but 44.9% of lanceolate complexes were abnormal in 5 weeks vibrated compared to 18.8% in sham. The largest vibration energies are peak kHz accelerations (approximately 100 000 m/s² ) from shock waves. The existing ISO 5349-1 standard excludes kHz vibrations, seriously underestimating vibration injury risk. The present study validates the rat tail, impact hammer vibration as a model for investigating irreversible nerve damage. Persistence of higher denervation difference after 5-week recovery suggests repeated vibration injury destroys the capability of lanceolate nerve endings to regenerate.

Acute Vibration Induces Peripheral Nerve Sensitization in a Rat Tail Model: Possible Role of Oxidative Stress and Inflammation

Prolonged occupational exposure to hand-held vibrating tools leads to pain and reductions in tactile sensitivity, grip strength and manual dexterity. The goal of the current study was to use a rat-tail vibration model to determine how vibration frequency influences factors related to nerve injury and dysfunction. Rats were exposed to restraint, or restraint plus tail vibration at 62.5 Hz or 250 Hz. Nerve function was assessed using the current perception threshold (CPT) test. Exposure to vibration at 62.5 and 250 Hz, resulted in a reduction in the CPT at 2000 and 250-Hz electrical stimulation (i.e. increased Aβ and Aδ, nerve fiber sensitivity). Vibration exposure at 250 Hz also resulted in an increased sensitivity of C-fibers to electrical stimulation and thermal nociception. These changes in nerve fiber sensitivity were associated with increased expression of interleukin (IL)-1β and tumor necrosis factor (TNF)-α in ventral tail nerves, and increases in circulating concentrations of IL-1 β in rats exposed to 250-Hz vibration. There was an increase in glutathione, but no changes in other measures of oxidative activity in the peripheral nerve. However, measures of oxidative stress were increased in the dorsal root ganglia (DRG). These changes in pro-inflammatory factors and markers of oxidative stress in the peripheral nerve and DRG were associated with inflammation, and reductions in myelin basic protein and post-synaptic density protein (PSD)-95 gene expression, suggesting that vibration-induced changes in sensory function may be the result of changes at the exposed nerve, the DRG and/or the spinal cord.

Detection of Snores Using Source Separation on an Emfit Signal

Snoring (SN) is an early sign of upper airway dysfunction, and it is strongly associated with obstructive sleep apnea. SN detection is important to monitor SN objectively and to improve the diagnostic sensitivity of sleep-disordered breathing. In this study, an automatic snore detection method using an electromechanical film transducer (Emfit) signal is presented. Representative polysomnographs of normal breathing and SN periods from 30 subjects were selected. Individual SN events were identified using source separation applying nonnegative matrix factorization deconvolution. The algorithm was evaluated using manual annotation of the polysomnographic recordings. According to our results, the sensitivity, and the positive predictive value of the developed method to reveal snoring from the Emfit signal were 82.81% and 86.29%, respectively. Compared to other approaches, our method adapts to the individual spectral snoring profile of the subject rather than matching a particular spectral profile, estimates the snoring intensity, and obtains the specific spectral profile of the snores in the epoch. Additionally, no training is necessary. This study suggests that it is possible to detect individual SN events with Emfit mattress, which can be used as a contactless alternative to more conventional methods such as piezo-snore sensors or microphones.

Over-vibration induced blood perfusion and vascular permeability changes may lead to vocal edema

OBJECTIVES/HYPOTHESIS

To observe blood perfusion and vascular permeability changes under varying vibration frequency exposures.

STUDY DESIGN

Animal model.

METHODS

Blood perfusion was measured using laser Doppler flowmetry in eight rabbit auricular vessels (four rabbits) under nonvibration, and 62.5-Hz/1-mm, 125-Hz/1-mm, and 250-Hz/0.5-mm vibration frequency/amplitude exposures. Another 12 rabbits were randomly divided into vibration only and vibration with histamine groups. After 3 hours of continuous 125-Hz, 1-mm amplitude vibration of the auricle, vascular permeability was analyzed by absorbance of Evans blue-albumin complex.

RESULTS

Significantly lower blood perfusion was observed in the vibration group, compared with no vibration exposure controls. Blood perfusion decreased 29 ± 16% as the vibration frequency was increased from 62.5 Hz to 125 Hz with the vibration amplitude constant at 1 mm. When the frequency was increased from 125 Hz to 250 Hz, while the amplitude was decreased from 1 mm to 0.5 mm, blood flow perfusion further decreased 29 ± 29%, and the decline tendency in blood perfusion showed no significant difference (P = .992). Meanwhile, in the vibration with histamine group, vascular permeability of the vibrated ears increased significantly compared to the nonvibrated ears (P = .005).

CONCLUSIONS

Overvibration of the vocal folds due to voice overuse or abuse may significantly reduce blood perfusion, and increase vascular permeability in the vocal fold in inflammatory situations, which may lead to the formation of vocal edema.

LEVEL OF EVIDENCE

NA Laryngoscope, 127:148-152, 2017.

Dependence of vascular damage on higher frequency components in the rat-tail model

Hand-Arm Vibration Syndrome (HAVS) is caused by hand-transmitted vibration in industrial workers. Current ISO guidelines (ISO 5349) might underestimate vascular injury associated with range of vibration frequencies near resonance. A rat-tail model was used to investigate the effects of higher frequencies >100 Hz on early vascular damage. 13 Male Sprague-Dawley rats (250 ± 15 gm) were used. Rat-tails were vibrated at 125 Hz and 250 Hz (49 m/s(2)) for 1D, 5D and 10D; D=days (4 h/day). Structural damage of the ventral artery was quantified by vacuole count using Toluidine blue staining whereas biochemical changes were assessed by nitrotyrosine (NT) staining. The results were analyzed using one-way repeated measures mixed-model ANOVA at p<0.05 level of significance. The structural damage increased at 125 Hz causing significant number of vacuoles (40.62 ± 9.8) compared to control group (8.36 ± 2.49) and reduced at 250 Hz (12.33 ± 2.98) compared to control group (8.36 ± 2.49). However, the biochemical alterations (NT-signal) increased significantly for 125 Hz (143.35 ± 5.8 gray scale value, GSV) and for 250 Hz (155.8 ± 7.35 GSV) compared to the control group (101.7 ± 4.18 GSV). Our results demonstrate that vascular damage in the form of structural and bio chemical disruption is significant at 125 Hz and 250 Hz. Hence the current ISO guidelines might underestimate vascular damage at frequencies>100 Hz.

Hand-arm vibration syndrome: a common occupational hazard in industrialized countries

Regular exposure to hand-transmitted vibration can result in symptoms and signs of peripheral vascular, neurological and other disorders collectively known as the hand-arm vibration syndrome (HAVS). A significant proportion of workers can suffer from HAVS after using vibrating power tools. HAVS is a chronic and progressive disorder. Early recognition and prevention is the key to managing vibrating tool exposures and health effects. This article gives a broad overview of the condition with a detailed account of its pathogenesis, identification and management.

Tissue vibration induces carotid artery endothelial dysfunction: a mechanism linking snoring and carotid atherosclerosis?

STUDY OBJECTIVES

We have previously identified heavy snoring as an independent risk factor for carotid atherosclerosis. In order to explore the hypothesis that snoring-associated vibration of the carotid artery induces endothelial dysfunction (an established atherogenic precursor), we utilized an animal model to examine direct effects of peri-carotid tissue vibration on carotid artery endothelial function and structure.

DESIGN

In supine anesthetized, ventilated rabbits, the right carotid artery (RCA) was directly exposed to vibrations for 6 h (peak frequency 60 Hz, energy matched to that of induced snoring in rabbits). Similarly instrumented unvibrated rabbits served as controls. Features of OSA such as hypoxemia, large intra-pleural swings and blood pressure volatility were prevented. Carotid endothelial function was then examined: (1) biochemically by measurement of tissue cyclic guanosine monophosphate (cGMP) to acetylcholine (ACh) and sodium nitroprusside (SNP); and (2) functionally by monitoring vessel relaxation with acetylcholine in a myobath.

MEASUREMENT AND RESULTS

Vessel cGMP after stimulation with ACh was reduced in vibrated RCA compared with unvibrated (control) arteries in a vibration energy dose-dependent manner. Vibrated RCA also showed decreased vasorelaxation to ACh compared with control arteries. Notably, after addition of SNP (nitric oxide donor), cGMP levels did not differ between vibrated and control arteries, thereby isolating vibration-induced dysfunction to the endothelium alone. This dysfunction occurred in the presence of a morphologically intact endothelium without increased apoptosis.

CONCLUSIONS

Carotid arteries subjected to 6 h of continuous peri-carotid tissue vibration displayed endothelial dysfunction, suggesting a direct plausible mechanism linking heavy snoring to the development of carotid atherosclerosis.

Vibration disrupts vascular function in a model of metabolic syndrome

Vibration-induced white finger (VWF) is a disorder seen in workers exposed to hand-transmitted vibration, and is characterized by cold-induced vasospasms and finger blanching. Because overweight people with metabolic syndrome are pre-disposed to developing peripheral vascular disorders, it has been suggested that they also may be at greater risk of developing VWF if exposed to occupational vibration. We used an animal model of metabolic syndrome, the obese Zucker rat, to determine if metabolic syndrome alters vascular responses to vibration. Tails of lean and obese Zucker rats were exposed to vibration (125 Hz, 49 m/s(2) r.m.s.) or control conditions for 4 h/d for 10 d. Ventral tail arteries were collected and assessed for changes in gene expression, levels of reactive oxygen species (ROS) and for responsiveness to vasomodulating factors. Vibration exposure generally reduced the sensitivity of arteries to acetylcholine (ACh)-induced vasodilation. This decrease in sensitivity was most apparent in obese rats. Vibration also induced reductions in vascular nitric oxide concentrations and increases in vascular concentrations of ROS in obese rats. These results indicate that vibration interferes with endothelial-mediated vasodilation, and that metabolic syndrome exacerbates these effects. These findings are consistent with idea that workers with metabolic syndrome have an increased risk of developing VWF.