History and Development of Nasometry
The study of nasal sounds, known as nasometry, began in the 1970s as speech language pathologists sought new techniques for quantifying and analyzing nasal air emissions during speech. Some of the earliest nasometry devices utilized nasal airflow sensors and pressure transducers to measure acoustic characteristics like nasalance scores. By the 1980s and 1990s, digital signal processing technologies allowed for more sophisticated analysis of nasal sounds through computerized nasometers. Today's nasometry devices can detect and evaluate aspects of nasal resonance like nasal air flow, pressure, timing, and frequency in great detail.
Measuring Nasal Airflow and Pressure
Most modern nasometry devices use a lightweight nasal cannula, similar to those used in hospitals, which is fitted into the nose. Nasometry Devices The cannula has two small tubes that run into both nostrils and are connected to sensitive pressure transducers. As the wearer speaks or makes different sounds, the transducers pick up subtle changes in airflow and pressure within the nasal cavity. Different sounds require more or less nasal airflow, while vowels tend to have lower nasalance scores than oral consonants. By quantifying these acoustic properties frame-by-frame, the nasometer can objectively measure a speaker's relative “nasalness.” Some models include a mask that fits over the nose and mouth to more accurately capture total oral-nasal resonance patterns during speech.
Analyzing Frequency Response and Timing
In addition to airflow and pressure, advanced nasometry uses fast Fourier transform algorithms to analyze the frequency response of nasal sounds in great detail. Certain pathological conditions, like nasal obstruction from a deviated septum, will distort the normal resonant frequency peaks observed during different phonemes. By tracking minor frequency fluctuations across the speech spectrum, clinicians can better diagnose nasal abnormalities and track the progress of treatment. More sophisticated nasometers also measure timing variables to quantify things like voice onset time during specific sounds. This helps objectively evaluate problems with speech motor planning and coordination that can contribute to hypernasality or hyponasality.
Clinical Applications of Nasometry
Nasometry has proven invaluable for diagnosing and monitoring a variety of nasal speech disorders. It provides an objective measure of hypernasality in conditions like cleft palate, submucosal cleft palate, and velopharyngeal insufficiency. Pre and postoperative nasometry scores aid in surgical planning and follow up. Nasometry is also useful in the diagnosis and management of nasal airway disorders, including nasal/sinus tumors, allergies, and septal deviations. Voice therapists employ nasometers to track nasal resonance changes during therapy for conditions causing hyperfunctional or hypofunctional nasal air emission patterns. Overall, nasometry delivers a clinically- validated means to quantify nasal sounds, guide treatment, and conduct research into nasal speech mechanics.
Reliability and Standardization of Nasometry Protocols
For nasometry to convey meaningful data both within and between clinical studies, reliability and standardization of test protocols are essential. Significant efforts have been made to establish reliable normative data and define what constitutes clinically abnormal nasalance scores. Standard test passages like the Rainbow Passage aim to control for factors like word content and frequency. Controlled vowel sounds are also routinely employed. Variability between nasometer brands requires score adjustments or correlation tables during multisite research. Stricter control of variables like microphone placement, head position, calibration, and acoustic environment boost nasometry's precision and repeatability as a diagnostic tool. Wider adoption of standardized protocols will strengthen nasometry's role in treatment planning and testing new interventions for craniofacial anomalies and other nasal speech disorders.
The Future of Nasometry
As technologies evolve, new capabilities are being added to nasometry devices. Some models now interface with computerized speech visualisation programs to integrate airflow and acoustic data with simultaneous video recording. This enhances visualization and analysis. Nasometers are increasingly portable and Wi-Fi enabled for telepractice applications. Miniaturized sensors may one day allow for ambulatory monitoring of nasal function during daily life activities. Artificial intelligence approaches also show promise for automating portions of nasometric analysis. Overall, as clinicians gain experience applying nasometry, and standardisation continues, it will likely assume an even greater role in objectively evaluating and optimising nasal speech function. Multidisciplinary collaboration between engineers, clinicians, and researchers ensures nasometry fulfills its promise to improve diagnosis and treatment outcomes for those affected by nasal communication disorders.
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