COCHLEAR FLUX MOTION AND ARTERIAL-PRESSURE REDUCTION IN GUINEA-PIG

Vasomotion, as a fundamental phenomenon of microvessels, exists in the cochlea of guinea pig. In the current study, the vasomotion and its r elation to arterial pressure reduction was studied in the guinea pig c ochlea, using laser Doppler flowmetry (LDF). Blood pressure (BP) in 25 guinea pigs was manipulated by a mechanical occluder placed around th e descending aorta or the inferior vena cava. Before thoractomy and ar tificial respiration, BP was 55.5 +/- 10.9 mmHg and no flux motion occ urred. Vasomotion became evident when BP was significantly lower (28.2 +/- 7.2 mmHg) than the mean BP after thoracotomy (37.3 +/- 8.3 mmHg) (t = 4.1536, p < 0.05). Vasomotion appeared during both continuous hyp otension and brief BP decreases caused by mechanical occlusion. During periods of continuous Aux motion, both increase and decrease in BP co uld weaken or abolish it. The pressure provoking the vasomotion was di fferent for each animal but the pressure range for a given animal was relatively stable. Mean frequency and amplitude of flux motion were 3. 8 +/- 0.6 cycles per min and 20.8 +/- 7.1% of the baseline. A negative linear relationship was found between amplitude and frequency. Oscill ations of LDF signal indicate that there is a synchronization of contr action and relaxation of cochlear microvessels or of the larger supply ing vessels to the cochlea. Manipulation of BP possibly initiates the fluctuating change in vascular tone by influencing the activity of pac emaker or feedbaclk mechanisms of cochlear vascular smooth muscles. Da ta in the current study suggest that (i) hypotension is a powerful fac tor to provoke vasomotion in the cochlea; (ii) pressure range to initi ate cochlear vasomotion is individual; (iii) frequency and amplitude o f flux motion seem to be pressure-dependent.