Abstract

Background: One of the most common yet least understood hyperfunctional voice disorders is muscle tension dysphonia (MTD). MTD is described as poorly regulated activity of the intrinsic and extrinsic laryngeal muscles leading to high levels of stiffness and tension in the vocal folds.The etiology of MTD remains unclear, but most MTD patients report having to produce an overly increased vocal effort under noisy environments. This an unconscious response, called the Lombard effect, where subjects increase the intensity and frequency. We hypothesize that MTD patients may be more sensitive to the lombard effect, due to a possible dysfunction in the integration of auditory feedback. Aims: To describe the acoustic, aerodynamic, biomechanical and neuronal cortical aspects of the Lombard effect in subjects with MTD and normal controls. Methods: Experiment 1: Physical component A group of 8 subjects with normal voice and 8 subjects with MTD was recruited. Subjects were asked to utter a series of vowels presented in images through a monitor. The images were presented during 5 seconds with a 5-second pause between stimuli. A total of 40 stimuli was distributed in 8 series of 5 images. The complete sequence was performed under 3 conditions: 1. Baseline 2. In noise (speech noise at 75 dB HL) 3. In quiet after a 5-minute pause For each condition, vocal function was assessed by high-speed videoendoscopy (VHS), aerodynamic measurements, neck surface accelerometer and acoustic measurements. Experiment 2: Neurophysiological component The cortical activity of 3 normal subjects was recorded using a 64-channel electroencephalograph (EEG). Each subject was asked to utter 16 series of 5 syllables with an 8-second pause between series and under 3 conditions described below. Acoustic and neck surface accelerometers signals were also obtained. To detect the events in the EEG recording, an onset detector is used to synchronize the events. 1. Baseline 2. In noise (speech noise at 85 dB HL) 3. In quiet after a 5-minute pause Preliminary results: Preliminary results suggested that subjects with MTD might be more sensitive to the Lombard effect, since they generate a greater variation of SPL and have greater difficulties to return to baseline conditions when the noise is removed. Regarding the biomechanical changes, all subjects presented an increase of the posterior closure during lombard effect, but the MTD patients exhibited greater vibratory asymmetry. Also in the aerodynamic measures this group show more changes in MFDR, RFE and H1-H2.