Effects of CO2 inhalation on cochlear blood circulation

The cochlear blood flow was measured with the microsphere method before, during and after CO2 inhalation in anesthetized rabbits. Different gas mixtures and exposure times were used. The greatest increase of cochlear blood flow was measured after 5 min inhalation of 7% CO2 in air (115%) and the least increase (44%) in animals breathing 7% CO2 in oxygen. The difference is explained as due to a vasoconstriction caused by a high oxygen tension counteracting the vasodilating effect of CO2. The treatment with CO2 of supposed vascular diseases in the cochlea is discussed and the negative effects due to respiratory acidosis are emphasized.

The effect of noise on cochlear blood flow in the conscious rabbit

The cochlear blood flow was measured with the microsphere method in unanesthetized rabbits, prior to and during noise-exposure. Different sound pressure levels were used: 100 dB, 115 dB and 120 dB. Some of the animals had the cervical sympathetic trunk cut unilaterally. The effects of the delivered noise on the organ of Corti were studied in other rabbits with scanning electron microscopy. In spite of ultrastructural changes indicating damage of sensory cells after 115 dB and 120 dB exposure no changes of the total cochlear blood flow could be observed. After unilateral section of the cervical sympathetic trunk the cochlear blood flow was less on the intact side (25%) already prior to noise exposure and the difference was not significantly affected by noise. Different sizes of microspheres were used: 8.2, 8.4, 8.7, 9,2 mum. The 8.2 and 8.4 mum-spheres seemed well fitted for measurements of cochlear blood flow but passed the cerebral capillaries to a high extent. Control experiments using both 8.2/8.4 mum-spheres and 15 mum-spheres were performed and the degree of passage in different tissues was estimated.

Noise and cochlear blood flow

The effect of noise after unilateral transection of the cervical sympathetic trunk on cochlear blood flow was studied in anesthetized cats. The sound pressure level was 100 dB and the exposure time 6 min. Neither noise nor sympathectomy were found to affect the blood flow.

Cochlear blood circulation studied with microspheres

The cochlear blood flow was studied with the microsphere method in guinea pigs, rats and cats. Results from experiments using different sizes of microspheres were compared and the effect of middle ear infection or perforation of the otic capsule on the cochlear microcirculation was investigated. Neither the opening of the cochlear bony wall nor the middle ear infection influenced the blood flow in the cochlea. 9- and 15-micrometer spheres were given simultaneously and the results were equivalent, indicating no more shunting of the smaller ones than of the bigger ones. Thus, the smaller spheres are to be preferred, since the smaller ones can be used in a larger number without negative effects on the general circulation. In cats, the cochlear blood circulation was determined before and during cervical sympathetic stimulation. Sympathetic stimulation caused a reduction of 25% of the cochlear blood flow.

The cochlear blood flow

Cochlear blood flow in the guinea pig was investigated using Tracer Sephadex 15 microspheres labelled with radioactive nuclides. A reference organ technique was used for quantitative measurements of cardiac output and the blood flow in the cochlear soft tissue, CNS and kidney. In some experiments the blood flow was measured at two occasions, either with 57Coor with 58Co-labelled microspheres. The results, including the size of cochlear blood flow are presented and discussed.