Cochlear Flux Motion and Arterial Pressure Reduction in Guinea Pig

Abstract

Vasomotion, as a fundamental phenomenon of microvessels, exists in the cochlea of guinea pig. In the current study, the vasomotion and its relation to arterial pressure reduction was studied in the guinea pig cochlea, using laser Doppler flowmetry (LDF). Blood pressure (BP) in 25 guinea pigs was manipulated by a mechanical occluder placed around the descending aorta or the inferior vena cava. Before thoractomy and artificial respiration, BP was 55.5 ± 10.9 mmHg and no flux motion occurred. 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 hypotension and brief BP decreases caused by mechanical occlusion. During periods of continuous flux motion, both increase and decrease in BP could weaken or abolish it. The pressure provoking the vasomotion was different 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. Oscillations of LDF signal indicate that there is a synchronization of contraction and relaxation of cochlear microvessels or of the larger supplying vessels to the cochlea. Manipulation of BP possibly initiates the fluctuating change in vascular tone by influencing the activity of pacemaker or feedbaclk mechanisms of cochlear vascular smooth muscles. Data in the current study suggest that (i) hypotension is a powerful factor to provoke vasomotion in the cochlea; (ii) pressure range to initiate cochlear vasomotion is individual; (iii) frequency and amplitude of flux motion seem to be pressure-dependent.

Key Words:

• vasomotion
• microcirculation
• blood pressure
• inner ear
• laser Doppler flowmetry.