Visualizing the invisible sound
Surprisingly, almost no otolaryngologist ever listens to the voice in a systematic way. Imagine otology without audiograms. Audiograms reveal patterns that the otologist can recognize and point the astute examiner to the appropriate anatomy or physiology which might be causing the impairment. Hoarseness, like hearing impairment, is also sound wave impairment and patterns of impairment are identifiable.
With sound, we have pitch, volume and clarity to be concerned with on our vocal exam, so it will be helpful to visualize their interaction. Let’s set up a graph correlating pitch with volume.
While this can graph can be created quite precisely (phonetogram), in my daily practice I am interested in using this graph in a clinical fashion, not as a precise measurement, but as a general guide to focus my visual examination where problems should be located. I am searching for a pattern of impairment. A given pattern on this graph will then direct my visual endoscopic exam.
Pitch graphed along the x-axis correlates roughly with a keyboard. If a vocally healthy male were examined throughout his vocal range at soft volume and then again at a louder volume, we could diagram his voice, noting where his comfortable speaking pitch was located and his vocal range.
We could diagram a female in the same way. Typically, everything would be shifted to the right in comparison to a male. The circle represents a typical comfortable speaking pitch which varies not only on sex, but on size of the person. A smaller person with a smaller larynx will have a vocal pattern shifted to the right. The painted areas represent the clear sounds that she could make throughout her soft and loud vocal ranges. A trained vocalist of either sex would typically have longer areas of coloration.
This graph represents the audible toolbox for the laryngologist. Maybe we could call it a laryngogram or clinical phonetogram.
In 1981 Hirano (Hirano, M. (1981). Clinical Examination of Voice. Vienna, Springer-Verlag.) postulated that Roughness and Breathiness could be utilized to identify a voice disorder. His working group suggested the GRBAS scale, where severities of 5 characteristics were rated (Grade, Roughness, Breathiness, Asthenia, Strain). Despite his aspirations and the frequency of the scale’s use in scientific literature, the scale has not lead to patterns that could identify the type of vocal impairment. However, the two parameters of roughness and breathiness (equivalent to huskiness in this book) I believe are key parameters that can point to a pattern that identifies the problem. These two parameters need more than a number estimating their intensity. They need to be correlated with pitch and volume to be meaningful.
If a patient was scored as a 2 on the breathiness scale and another patient was scored a 4 on the breathiness scale, I would have no clue from these numbers what the difference in their voice problem might be. I could barely start a differential diagnosis.
However, if I know that an individual leaks air at low pitch, low volume and there is no perceptible leak at high pitch, high volume, I can already start a differential diagnosis of disorders that are likely in this individual and I have already started ruling out others. Presbyphonia, muscle atrophy, and paresis of the anterior branch of the recurrent laryngeal nerve would be strong potential matches given just this singular piece of information. Tumors, neurologic tremor, spasms, and superior laryngeal nerve injuries would all be unlikely candidates for a diagnosis in this case. We haven’t even discussed the patient’s history or scored their roughness parameter, yet we have a good idea where we are headed. The pattern of sound impairment is valuable information.
A prediction
It seems highly likely that someday a patient with hoarseness could record a vocal glide from their lowest to highest pitch at soft volume and again at a loud volume and a computer with sufficient processing power and previous data could use artificial intelligence to match the patterns of areas of clarity, areas of roughness and areas of breathiness up with historical controls and make a fairly accurate prediction as to what endoscopy will show. Until that time, I find it helpful to have a battery of tests on the voice that I can use to elicit vocal impairments in the patient complaining of hoarseness.