An experimental setup with a laser fiber optic probe has been developed, and the vibration dynamics of the vocal folds (VFs) in the larynx of rabbits have been studied. VF vibrations were excited by a variable pressure air stream. We found that, at an air flow pressure of 50 to 60 mm Hg, VFs generate a white vibration noise in the frequency range of 100 Hz to 10 kHz. The spectrum of excited vibration frequencies becomes narrower when the air flow pressure decreases from 10 to 20 mm Hg, and three discrete lower fundamental frequencies of intrinsic mechanical vibrations of individual VFs are excited at about 360, 750, and 1100 Hz, simultaneously with narrow peaks in the high-frequency region at about 3, 6, and 8 kHz, respectively. The characteristic discrete vibration frequencies of VFs are most efficiently excited near the air flow exhaustion at a pressure of 1 to 5 mm Hg. We detected a difference in the fundamental frequencies of the excited vibrations between intact VF and those treated for a scar defect in one of the VFs. The frequencies of the lowest intrinsic excited modes of the treated VF are slightly higher compared with untreated (intact) VF. The increase in the vibration frequencies may be explained by the growth of VF's stiffness related to the formation of scar tissue. The mentioned frequency difference was registered with confidence and may serve as a basis for a mildly invasive instrumental diagnostics in the therapy of VF disorders as an aid to a traditional examination and subjective assessment of VF states.
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