Harold A. Dengerink

The Laser Doppler: A Non-invasive Measure of Cochlear Blood Flow

The present investigation demonstrates the utility of the laser Doppler flowmeter to provide a measure of cochlear blood flow dynamics. Cochlear and cutaneous blood flow were compared with arterial blood pressure during and following exposure to Angiotensin II, 5% carbon monoxide, 100% oxygen, mannitol, and saline. The observations indicate that: 1) cochlear blood flow generally parallels cutaneous blood flow; however, 2) when cutaneous beds vasoconstrict (e.g., AII, alpha-agonists), cochlear blood flow parallels blood pressure; and, 3) under the influence of agents that affect peripheral and central circulation (5% CO, 100% O2), cochlear blood flow may dissociate from cutaneous blood flow and blood pressure. The implications of these findings are discussed in terms of local control mechanisms that may be involved in the inner ear vasculature.

The effects of noise on histological measures of the cochlear vasculature and red blood cells: A review

This paper compiles the results from seven experiments which have investigated noise exposure effects on histological measures of the cochlear vasculature and red blood cells. Two of these studies included at least two experimental conditions and all evaluated numerous histological parameters in several cochlear vessels. The combined results suggest that noise has a consistent general effect of reducing apparent cochlear blood flow as indicated by decreased RBC density, increased aggregation of RBCs, increased variability in RBC density, decreased number of RBC columns, increased vessel lumen irregularity and encroachment of perivascular cells upon the lumen wall. When considered at the level of the individual vessels, however, inconsistent results were observed. Fewer effects were noted in experiments which permitted animals to survive after the noise exposure than in those which sacrificed the animals immediately. Impulse noise resulted in more frequent vascular sequelae than did continuous noise. Further, impulse noise more frequently influenced vessels of the external wall than did continuous noise.

Potential role of angiotensin II in noise-induced increases in inner ear blood flow

Guinea pigs were exposed to 120 dB white noise for 30 min and evidenced a four-fold elevation in plasma concentration of the potent vasoconstricting hormone angiotensin II (AII). Anesthetized animals received intra-arterial injections of AII at doses that approximated the endogenous levels measured following noise exposure. A marked decrease in skin blood flow was observed with a concomitant increase in cochlear blood flow as measured by laser Doppler flowmeters. Increased cochlear blood flow appeared to be secondary to the increases in systemic blood pressure induced by AII. These findings suggest that cochlear blood flow may increase during periods of intense noise exposure.

Aggression as a function of the intensity and pattern of attack

Abstract Forty S s competed with an opponent in a reaction time task to avoid receiving shock. The opponent provided either consistently high intensity attack, increasing, decreasing, or consistently low attack. The S s shock settings for the opponent on each trial and ratings of the opponent after the task served as dependent measures. High intensity attack resulted in high intensity counterattack and negative ratings of the opponent. Low intensity attack resulted in low intensity counterattack and relatively positive ratings for the opponent. Decreasing attack resulted in decreasing counterattack and positive ratings of the opponent. Increasing attack resulted in increasing counterattack and comparatively high aggression ratings of the opponent.

The Effect of Noise and Carbogen on Cochlear Vasculature

Histological measures of cochlear vasculature and blood flow were examined in 24 guinea pigs. Six animals were exposed to white noise at 120 dB SPL while breathing carbogen (10% CO2 and 90% O2) for 30 min. Six subjects were noise exposed while breathing air. Six breathed carbogen without noise exposure and six served as unexposed air-breathing controls. The statistically significant results indicate that noise resulted in reduced blood supply to the cochlea and that carbogen increased cochlear blood flow. When animals were exposed to both noise and carbogen, carbogen tended to counteract the reduced blood supply effects of noise.

Cochlear blood flow autoregulation in Wistar-Kyoto rats

Wistar-Kyoto rats (WKY) were intra-arterially infused with angiotensin II (AII) or phenylephrine for 10 min. Both vasoactive compounds produced an initial increase in cochlear blood flow (CoBF) as measured by laser Doppler flowmetry, followed by a slow steady return to baseline, despite sustained elevations in systemic blood pressure. These results suggest autoregulation of CoBF in the WKY rat. In a second experiment. All was infused directly into the anterior inferior cerebellar artery (AICA) which feeds the cochlear artery. Significant reductions in CoBF were noted without changes in systemic blood pressure. Pretreatment with the specific angiotensin-receptor antagonist, sarthran (Sar1, Thr8-AII), diminished subsequent AII-induced reductions in CoBF. These results indicate that AII binding to vascular receptors may induce vasoconstriction in the supplying vessels of the cochlea, and thus, the interaction of blood-borne AII and vascular angiotensin receptors may participate in the autoregulation of CoBF.

Ovarian steroid and vasoconstrictor effects on cochlear blood flow

Ovariectomized rats received intra-arterial infusions of phenylephrine and nicotine. Estrogen treatment for five days prior to these challenges diminished laser Doppler measures of cochlear blood flow (CBF) responses to phenylephrine and blood pressure responses to nicotine. Progesterone enhanced CBF responses to both phenylephrine and nicotine; combined progesterone and estrogen treatment enhanced blood pressure responses to phenylephrine. These results suggest that ovarian steroid-mediated cardiovascular effects may influence cochlear blood flow and potentially hearing functions.

The effects of nicotine on laser Doppler measures of cochlear blood flow

Anesthetized guinea pigs were given arterial bolus injections of saline or varying nicotine concentrations. Blood flow through the cochlea and skin were measured via laser Doppler and arterial blood pressure via an arterial cannula. Cochlear blood flow increased with low doses of nicotine but decreased with the highest dose, while blood pressure increased and skin flow decreased with all doses of nicotine. Control injections of saline vehicle had only minor and transient effects.

Angiotensin II-induced changes in cochlear blood flow and blood pressure in normotensive and spontaneously hypertensive rats

Previous investigations in our laboratory have measured significant increases in the circulating levels of the potent vasoconstrictive hormone, angiotensin II (AII; 26 and 64 pg/100 microliters plasma, normal and noise exposed, respectively), during and following noise exposure in the alert rat (Wright et al., 1981). In the present study, these levels were approximated through intra-arterial infusion in the anesthetized spontaneously hypertensive rat (SHR) and normotensive Wistar-Kyoto (WKY) rat. Laser Doppler flowmeter measurements of cochlear blood flow (CBF) indicated that despite equivalent AII-induced elevations in systemic blood pressure, CBF in the SHR did not increase to the levels measured in the WKY. Pretreatment with the specific angiotensin receptor antagonist sarile, (Sar1,Ile8-AII), reduced AII-induced elevations in systemic blood pressure in members of both strains, but did not change the overall pattern of CBF. These results indicate that SHRs may have a compromised cochlear circulation that is refractory to increases in systemic blood pressure.

Individual differences in aggressive responses to attack: Internal-external locus of control and field dependence-independence.

Abstract Two experiments assessed the effect of individual differences on aggression. In both studies subjects were exposed to opponents in the competitive reaction time task who decreased the intensity of their attack from high to low, remained constantly moderate in their attack, or increased the intensity of their attack from low to high. In the first experiment Internal Locus of Control subjects consistently set high intensity shocks in response to high intensity attack and low shocks in response to mild attack. External subjects showed relatively minor variations in their aggressive responses to varying intensities of attack. In the second experiment field-independent subjects set more intense shocks than field-dependent subjects only in the Decreasing attack condition.