Cochlear Blood Flow: The Effect of Noise at 60 Minutes' Exposure

Abstract

\s=b\The effect of 60 minutes of exposure to high-frequency (10-to 40-kHz), hi gh\ x=req-\ intensity (115-dB) noise on the cochlear blood flow (CoBF) was investigated in adult gerbils. The CoBF was measured with a newly improved microsphere method. The number of microspheres in cochlear tissue that had been dissected by the surface preparation technique was assessed by direct counting. Our experiments have indicated that the CoBF is elevated even after 60 minutes of noise exposure. This was true particularly in the areas where these frequencies stimulate the cochlea. The noise also increased CoBF in the opposite ear in areas not corresponding to the stimulation frequencies (second and third turn). This phenomenon is under further investigation. (Arch Otolaryngol Head Neck Surg 1987;113:36-39) The harmful effect of noise on hear¬ ing has been known for a long time. It has been investigated both in people and in experimental animal models. Our knowledge about its mechanism is limited, however, and some earlier observations15 are con¬ troversial.Contrary to most earlier observations that described vasoconstriction of the arterioles in the inner ear after exposure to loud noise, we have observed that short (13-minute) expo¬ sure to high-frequency loud noise (113 dB) caused a substantial increase in the cochlear blood flow (CoBF) in the first turn of the exposed ear. Since this may be the effect of only shortterm noise exposure, we decided to study this phenomenon further. MATERIALS AND METHODSThe experiments were performed on 16 adult gerbils weighing 62 to 76 g that were anesthetized with allobarbital and urethan (Dial) (0.5 mL/kg) and alphadione (Althesin) (25 mg/kg). Before the noise exposure, one catheter was inserted into the left auricle of the heart for injection of the microspheres and a second catheter was inserted into the iliac artery for collection of the reference blood sample. The injected sample contained approximately 6 X 10* microsphere, 10.1 pm in diameter, sus¬ pended in 0.5 mL of 0.9% sodium chloride with a trace of polysorbate 80. The rate of withdrawal (reference blood flow) was set at 0.165 mL/min. This withdrawal was started shortly before the injection of the microspheres and continued one minute after the injection of the microspheres was completed, at which point the animals were killed by intracardiac injection of potassium chloride. The blood pressure was monitored by a pressure transducer (P 23) through the Y-branched cannula inserted in the iliac artery.The cochleas were then removed from the dead animals and fixed overnight in a glutaraldehyde -paraformaldehyde mix¬ ture at room temperature. Décalcification was started the next day by placing the cochleas in buffered 10% edetic acid, which was then changed daily for fresh solution. After décalcification, the cochleas were dissected in phosphate buffer, and the pieces of tissue were mounted in glycerin. Details of the dissection technique were described earlier.6In each turn, tissue was dissected and CoBF measured in three portions:...

Noise induced changes in the expression of p38/MAPK signaling proteins in the sensory epithelium of the inner ear

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Noise-induced changes in red blood cell velocity in lateral wall vessels of the rat cochlea

“…Ryan et al (1988) found histologic and autoradiographic evidence of small increases in co&ear blood fow in response to 85 dB SPL, but not at higher intensities. Prazma et al (1983Prazma et al ( , 1987 also observed an increase in co&ear blood flow in response to noise at 113 dB for 13 min and 115 dB for 60 min, as indicated by trapped microspheres.…”

Sarthran Preserves Cochlear Microcirculation and Reduces Temporary Threshold Shifts after Noise Exposure

“…The first contested issue with this hypothesis regards the influence of noise on cochlear microcirculation. Previous studies show that loud sound may increase [4][5][6] or decrease [7][8][9][10] cochlear blood flow (CBF). Other studies found no change in cochlear microcirculation after noise exposure.…”