Evidence for frequency-dependent arterial damage in vibrated rat tails

Abstract

The effects of single 4-hr bouts of continuous 30, 60, 120, and 800 Hz tail vibration (49 m/sec 2 , root mean squared) were compared to assess frequencyamplitude-related structural damage of the ventral caudal artery. Amplitudes were 3.9, 0.98, 0.24, and 0.0055 mm, respectively. Vibrated, sham-vibrated, and normal arteries were processed for light and electron microscopy. The Curry rat tail model of hand-arm vibration (Curry et al. Muscle Nerve 2002; 25:527-534) proved well-suited for testing multiple frequencies. NFATc3 immunostaining, an early marker of cell damage, increased in smooth muscle and endothelial cells after 30, 60, and 120 Hz but not 800 Hz. Increased vacuolization, which is indicative of smooth muscle contraction, occurred for all frequencies except 800 Hz. Vacuoles increased in both endothelial and smooth muscle cells after 60 and 120 Hz. Only 30 Hz showed pronounced smooth muscle cell vacuolization along the internal and external elastic membranes, suggesting stretch-mediated contraction from the large amplitude shear stress. Discontinuities in toluidine blue staining of the internal elastic membrane (IEM) increased for all frequencies, indicating vibration-induced structural weakening of this structure. Patches of missing IEM and overlying endothelium occurred in ϳ 5% of arteries after 60, 120, and 800 Hz. The pattern of damage after 800 Hz suggests that the IEM is disrupted because it resonates at this frequency. Vibration acceleration stress and smooth muscle contraction appear to be the major contributors to arterial damage. The pattern of vibrationinduced arterial damage of smooth muscle and endothelial cells is frequencyamplitude-dependent.

Effects of temperature on vibration‐induced damage in nerves and arteries

“…Our previous studies of vibration at room temperature showed that the formation of vacuoles in vascular smooth muscle cells was directly correlated with vasoconstriction, that is, contraction of smooth muscle cells. 9 The present findings for tails vibrated in cold temperatures are somewhat divergent, because, in spite of small arterial lumens, there were few smooth-muscle-cell vacuoles. When smooth muscle cells contract vigorously, cell- surface protrusions emerge at multiple sites.…”

Vibration Disrupts Vascular Function in a Model of Metabolic Syndrome

“…These results suggest that the effects of vibration on the peripheral vascular system are in part due to an organism's physiological response to vibration, and are not solely a result of the direct effects of vibration on the tissue. However, data collected in rats 17,32,33) and in humans 21,34,35) have demonstrated that both the shear and bending stresses of soft tissues, and the responses of the vascular system to vibration, are frequency and amplitude dependent. These data indicate that vibration also has some direct effects on vascular function.…”

Vibration Causes Acute Vascular Injury in a Two‐Step Process: Vasoconstriction and Vacuole Disruption

“…As previously described rats were restrained in tubular cages on a nonvibrating platform with their tails taped to a vibrating stage (Curry et al, 2002(Curry et al, , 2005a. In most instances they slept during vibration.…”

“…Vasoconstriction has been demonstrated as a very early effect of vibration in the ''rat-tail vibration model'' which simulates hand-transmitted vibration (Curry et al, 2002(Curry et al, , 2005a. When exposed to vibration, rat-tail arteries exhibit morphological signs of vasoconstriction, including narrowed lumens, tightly folded internal elastic membranes with endothelial cells pinched between their folds, and vacuoles in the SMC (Govindaraju et al, 2006a,b).…”