Minimum intensities of white noise which produce the vasomotor response

Sound stimulation-induced vasomotor reflex in the central artery of the rabbit ear

Effects of sound stimulation on the central artery of the rabbit ear were studied as a somato-autonomic reflex. Vasoconstriction and dilatation, caused by metronome sound stimulation, were estimated from the temperature fluctuations in the central artery of the ear, measured by a thermistor. To enhance the detection of temperature rises, moderately high background levels of arterial tone were established by exposing the tips of the ears to water at a temperature of 10 degrees C or 5 degrees C, prior to sound stimulation. A fall in arterial temperature due to vasoconstriction was observed immediately after the start of the 1-min sound stimulation, with a subsequent temperature rise which overshot the original basal level due to vasodilatation. A positive correlation between the ear temperature before sound stimulation and the temperature fall (p < 0.01), and a negative correlation between the ear temperature and the temperature rise (p < 0.05) were obtained. The temperature fall was blocked by phenoxybenzamine (9 mg/kg, i.p., p < 0.01). The subsequent rise was not influenced by atropine (3 mg/kg, i.p.) or phenoxybenzamine, however, it was attenuated by hexamethonium (6 mg/kg, i.p., p < 0.05). The temperature fall at the beginning of sound stimulation was related to alpha-adrenergic mechanism. The subsequent temperature rise was thought to be related to parasympathetic mechanism, excluding cholinergic mechanism.

Vasomotor response to pure tones using photoplethysmography

Digital photoplethysmography has been applied to the determination of hearing levels for pure tones. On average, the levels established were some 30 dB higher than those obtained with conventional pure-tone audiometry. Intervals between stimuli, however, were shown to have a significant effect upon the responses and the evidence suggests that recovery periods of 5 min may be required to obtain stable responses. The resulting testing tone involved is probably too long for most practical purposes.